RFR(L) 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents
Reingruber, Richard
richard.reingruber at sap.com
Wed Apr 1 06:15:12 UTC 2020
Hi Martin,
> thanks for addressing all my points. I've looked over webrev.5 and I'm satisfied with your changes.
Thanks!
> I had also promised to review the tests.
Thanks++
I appreciate it very much, the tests are many lines of code.
> test/jdk/com/sun/jdi/EATests.java
> This is a substantial amount of tests which is appropriate for a such a large change. Skipping some subtests with UseJVMCICompiler makes sense because it doesn't provide the necessary JVMTI functionality, yet.
> Nice work!
> I also like that you test with and without BiasedLocking. Your tests will still be fine after BiasedLocking deprecation.
Hope so :)
> Very minor nits:
> - 2 typos in comment above EARelockingNestedInflatedTarget: "lockes are ommitted" (sounds funny)
> - You sometimes write "graal" and sometimes "Graal". I guess the capital G is better. (Also in EATestsJVMCI.java.)
> test/jdk/com/sun/jdi/EATestsJVMCI.java
> EATests with Graal enabled. Nice that you support Graal to some extent. Maybe Graal folks want to enhance them in the future. I think this is a good starting point.
Will change this in the next webrev.
> Conclusion: Looks good and not trivial :-)
> Now, you have one full review. I'd be ok with covering 2nd review by partial reviews.
> Compiler and JVMTI parts are not too complicated IMHO.
> Runtime part should get at least one additional careful review.
Thanks a lot,
Richard.
-----Original Message-----
From: Doerr, Martin <martin.doerr at sap.com>
Sent: Dienstag, 31. März 2020 16:01
To: Reingruber, Richard <richard.reingruber at sap.com>; 'Robbin Ehn' <robbin.ehn at oracle.com>; Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; David Holmes <david.holmes at oracle.com>; Vladimir Kozlov (vladimir.kozlov at oracle.com) <vladimir.kozlov at oracle.com>; serviceability-dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-dev at openjdk.java.net
Subject: RE: RFR(L) 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents
Hi Richard,
thanks for addressing all my points. I've looked over webrev.5 and I'm satisfied with your changes.
I had also promised to review the tests.
test/hotspot/jtreg/serviceability/jvmti/Heap/IterateHeapWithEscapeAnalysisEnabled.java
Thanks for updating the @summary comment. Looks good in webrev.5.
test/hotspot/jtreg/serviceability/jvmti/Heap/libIterateHeapWithEscapeAnalysisEnabled.c
JVMTI agent for object tagging and heap iteration. Good.
test/jdk/com/sun/jdi/EATests.java
This is a substantial amount of tests which is appropriate for a such a large change. Skipping some subtests with UseJVMCICompiler makes sense because it doesn't provide the necessary JVMTI functionality, yet.
Nice work!
I also like that you test with and without BiasedLocking. Your tests will still be fine after BiasedLocking deprecation.
Very minor nits:
- 2 typos in comment above EARelockingNestedInflatedTarget: "lockes are ommitted" (sounds funny)
- You sometimes write "graal" and sometimes "Graal". I guess the capital G is better. (Also in EATestsJVMCI.java.)
test/jdk/com/sun/jdi/EATestsJVMCI.java
EATests with Graal enabled. Nice that you support Graal to some extent. Maybe Graal folks want to enhance them in the future. I think this is a good starting point.
Conclusion: Looks good and not trivial :-)
Now, you have one full review. I'd be ok with covering 2nd review by partial reviews.
Compiler and JVMTI parts are not too complicated IMHO.
Runtime part should get at least one additional careful review.
Best regards,
Martin
> -----Original Message-----
> From: Reingruber, Richard <richard.reingruber at sap.com>
> Sent: Montag, 30. März 2020 10:32
> To: Doerr, Martin <martin.doerr at sap.com>; 'Robbin Ehn'
> <robbin.ehn at oracle.com>; Lindenmaier, Goetz
> <goetz.lindenmaier at sap.com>; David Holmes <david.holmes at oracle.com>;
> Vladimir Kozlov (vladimir.kozlov at oracle.com)
> <vladimir.kozlov at oracle.com>; serviceability-dev at openjdk.java.net;
> hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-
> dev at openjdk.java.net
> Subject: RE: RFR(L) 8227745: Enable Escape Analysis for Better Performance
> in the Presence of JVMTI Agents
>
> Hi,
>
> this is webrev.5 based on Robbin's feedback and Martin's review - thanks! :)
>
> The change affects jvmti, hotspot and c2. Partial reviews are very welcome
> too.
>
> Full: http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.5/
> Delta:
> http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.5.inc/
>
> Robbin, Martin, please let me know, if anything shouldn't be quite as you
> wanted it. Also find my
> comments on your feedback below.
>
> Robbin, can I count you as Reviewer for the runtime part?
>
> Thanks, Richard.
>
> --
>
> > DeoptimizeObjectsALotThread is only used in compileBroker.cpp.
> > You can move both declaration and definition to that file, no need to
> clobber
> > thread.[c|h]pp. (and the static function deopt_objs_alot_thread_entry)
>
> Done.
>
> > Does JvmtiDeferredUpdates really need to be in thread.hpp, can't be in it's
> own
> > hpp file? It doesn't seem right to add JVM TI classes into thread.hpp.
>
> I moved JvmtiDeferredUpdates to vframe_hp.hpp where preexisting
> jvmtiDeferredLocalVariableSet is
> declared.
>
> > src/hotspot/share/code/compiledMethod.cpp
> > Nice cleanup!
>
> Thanks :)
>
> > src/hotspot/share/code/debugInfoRec.cpp
> > src/hotspot/share/code/debugInfoRec.hpp
> > Additional parmeters. (Remark: I think "non_global_escape_in_scope"
> would read better than "not_global_escape_in_scope", but your version is
> consistent with existing code, so no change request from my side.) Ok.
>
> I've been thinking about this too and finally stayed with
> not_global_escape_in_scope. It's supposed
> to mean an object whose escape state is not GlobalEscape is in scope.
>
> > src/hotspot/share/compiler/compileBroker.cpp
> > src/hotspot/share/compiler/compileBroker.hpp
> > Extra thread for DeoptimizeObjectsALot. (Remark: I would have put it into
> a follow up change together with the test in order to make this webrev
> smaller, but since it is included, I'm reviewing everything at once. Not a big
> deal.) Ok.
>
> Yes the change would be a little smaller. And if it helps I'll split it off. In
> general I prefer
> patches that bring along a suitable amount of tests.
>
> > src/hotspot/share/opto/c2compiler.cpp
> > Make do_escape_analysis independent of JVMCI capabilities. Nice!
>
> It is the main goal of the enhancement. It is done for C2, but could be done
> for JVMCI compilers
> with just a small effort as well.
>
> > src/hotspot/share/opto/escape.cpp
> > Annotation for MachSafePointNodes. Your added functionality looks
> correct.
> > But I'd prefer to move the bulky code out of the large function.
> > I suggest to factor out something like has_not_global_escape and
> has_arg_escape. So the code could look like this:
> > SafePointNode* sfn = sfn_worklist.at(next);
> > sfn->set_not_global_escape_in_scope(has_not_global_escape(sfn));
> > if (sfn->is_CallJava()) {
> > CallJavaNode* call = sfn->as_CallJava();
> > call->set_arg_escape(has_arg_escape(call));
> > }
> > This would also allow us to get rid of the found_..._escape_in_args
> variables making the loops better readable.
>
> Done.
>
> > It's kind of ugly to use strcmp to recognize uncommon trap, but that seems
> to be the way to do it (there are more such places). So it's ok.
>
> Yeah. I copied the snippet.
>
> > src/hotspot/share/prims/jvmtiImpl.cpp
> > src/hotspot/share/prims/jvmtiImpl.hpp
> > The sequence is pretty complex:
> > VM_GetOrSetLocal element initialization executes EscapeBarrier code
> which suspends the target thread (extra VM Operation).
>
> Note that the target threads have to be suspended already for
> VM_GetOrSetLocal*. So it's mainly the
> synchronization effect of EscapeBarrier::sync_and_suspend_one() that is
> required here. Also no extra
> _handshake_ is executed, since sync_and_suspend_one() will find the
> target threads already
> suspended.
>
> > VM_GetOrSetLocal::doit_prologue performs object deoptimization (by VM
> Thread to prepare VM Operation with frame deoptimization).
> > VM_GetOrSetLocal destructor implicitly calls EscapeBarrier destructor
> which resumes the target thread.
> > But I don't have any improvement proposal. Performance is probably not a
> concern, here. So it's ok.
>
> > VM_GetOrSetLocal::deoptimize_objects deoptimizes the top frame if it
> has non-globally escaping objects and other frames if they have arg escaping
> ones. Good.
>
> It's not specifically the top frame, but the frame that is accessed.
>
> > src/hotspot/share/runtime/deoptimization.cpp
> > Object deoptimization. I have more comments and proposals, here.
> > First of all, handling recursive and waiting locks in relock_objects is tricky,
> but looks correct.
> > Comments are sufficient to understand why things are done as they are
> implemented.
>
> > BiasedLocking related parts are complex, but we may get rid of them in the
> future (with BiasedLocking removal).
> > Anyway, looks correct, too.
>
> > Typo in comment: "regularily" => "regularly"
>
> > Deoptimization::fetch_unroll_info_helper is the only place where
> _jvmti_deferred_updates get deallocated (except JavaThread destructor).
> But I think we always go through it, so I can't see a memory leak or such kind
> of issues.
>
> That's correct. The compiled frame for which deferred updates are allocated
> is always deoptimized
> before (see EscapeBarrier::deoptimize_objects()). This is also asserted in
> compiledVFrame::update_deferred_value(). I've added the same assertion
> to
> Deoptimization::relock_objects(). So we can be sure that
> _jvmti_deferred_updates are deallocated
> again in fetch_unroll_info_helper().
>
> > EscapeBarrier::deoptimize_objects: ResourceMark should use
> calling_thread().
>
> Sure, well spotted!
>
> > You can use MutexLocker and MonitorLocker with Thread* to save the
> Thread::current() call.
>
> Right, good hint. This was recently introduced with 8235678. I even had to
> resolve conflicts. Should
> have done this then.
>
> > I'd make set_objs_are_deoptimized static and remove it from the
> EscapeBarrier interface because I think it shouldn't be used outside of
> EscapeBarrier::deoptimize_objects.
>
> Done.
>
> > Typo in comment: "we must only deoptimize" => "we only have to
> deoptimize"
>
> Replaced with "[...] we deoptimize iff local objects are passed as args"
>
> > "bool EscapeBarrier::deoptimize_objects(intptr_t* fr_id)" is trivial and
> barrier_active() is redundant. Implementation can get moved to hpp file.
>
> Ok. Done.
>
> > I'll get back to suspend flags, later.
>
> > There are weird cases regarding _self_deoptimization_in_progress.
> > Assume we have 3 threads A, B and C. A deopts C, B deopts C, C deopts C.
> C can set _self_deoptimization_in_progress while A performs the handshake
> for suspending C. I think this doesn't lead to errors, but it's probably not
> desired.
> > I think it would be better to use only one "wait" call in
> sync_and_suspend_one and sync_and_suspend_all.
>
> You're right. We've discussed that face-to-face, but couldn't find a real issue.
> But now, thinking again, a reckon I found one:
>
> 2808 // Sync with other threads that might be doing deoptimizations
> 2809 {
> 2810 // Need to switch to _thread_blocked for the wait() call
> 2811 ThreadBlockInVM tbivm(_calling_thread);
> 2812 MonitorLocker ml(EscapeBarrier_lock,
> Mutex::_no_safepoint_check_flag);
> 2813 while (_self_deoptimization_in_progress) {
> 2814 ml.wait();
> 2815 }
> 2816
> 2817 if (self_deopt()) {
> 2818 _self_deoptimization_in_progress = true;
> 2819 }
> 2820
> 2821 while (_deoptee_thread->is_ea_obj_deopt_suspend()) {
> 2822 ml.wait();
> 2823 }
> 2824
> 2825 if (self_deopt()) {
> 2826 return;
> 2827 }
> 2828
> 2829 // set suspend flag for target thread
> 2830 _deoptee_thread->set_ea_obj_deopt_flag();
> 2831 }
>
> - A waits in 2822
> - C is suspended
> - B notifies all in resume_one()
> - A and C wake up
> - C wins over A and sets _self_deoptimization_in_progress = true in 2818
> - C does the self deoptimization
> - A executes 2830 _deoptee_thread->set_ea_obj_deopt_flag()
>
> C will self suspend at some undefined point. The resulting state is illegal.
>
> > I first thought it'd be better to move ThreadBlockInVM before wait() to
> reduce thread state transitions, but that seems to be problematic because
> ThreadBlockInVM destructor contains a safepoint check which we shouldn't
> do while holding EscapeBarrier_lock. So no change request.
>
> Yes, would be nice to have the state change only if needed, but for the
> reason you mentioned it is
> not quite as easy as it seems to be. I experimented as well with a second
> lock, but did not succeed.
>
> > Change in thred_added:
> > I think the sequence would be more comprehensive if we waited for
> deopt_all_threads in Thread::start and all other places where a new thread
> can run into Java code (e.g. JVMTI attach).
> > Your version makes new threads come up with suspend flag set. That looks
> correct, too. Advantage is that you only have to change one place
> (thread_added). It'll be interesting to see how it will look like when we use
> async handshakes instead of suspend flags.
> > For now, I'm ok with your version.
>
> I had a version that did what you are suggesting. The current version also has
> the advantage, that
> there are fewer places where a thread has to wait for ongoing object
> deoptimization. This means
> viewer places where you have to worry about correct thread state
> transitions, possible deadlocks,
> and if all oops are properly Handle'ed.
>
> > I'd only move MutexLocker ml(EscapeBarrier_lock...) after if (!jt-
> >is_hidden_from_external_view()).
>
> Done.
>
> > Having 4 different deoptimize_objects functions makes it a little hard to
> keep an overview of which one is used for what.
> > Maybe adding suffixes would help a little bit, but I can also live with what
> you have.
> > Implementation looks correct to me.
>
> 2 are internal. I added the suffix _internal to them. This leaves 2 to choose
> from.
>
> > src/hotspot/share/runtime/deoptimization.hpp
> > Escape barriers and object deoptimization functions.
> > Typo in comment: "helt" => "held"
>
> Done in place already.
>
> > src/hotspot/share/runtime/interfaceSupport.cpp
> > InterfaceSupport::deoptimizeAllObjects() is only used for
> DeoptimizeObjectsALot = 1.
> > I think DeoptimizeObjectsALot = 2 is more important, but I think it's not bad
> to have DeoptimizeObjectsALot = 1 in addition. Ok.
>
> I never used DeoptimizeObjectsALot = 1 that much. It could be more
> deterministic in single threaded
> scenarios. I wouldn't object to get rid of it though.
>
> > src/hotspot/share/runtime/stackValue.hpp
> > Better reinitilization in StackValue. Good.
>
> StackValue::obj_is_scalar_replaced() should not return true after calling
> set_obj().
>
> > src/hotspot/share/runtime/thread.cpp
> > src/hotspot/share/runtime/thread.hpp
> > src/hotspot/share/runtime/thread.inline.hpp
> > wait_for_object_deoptimization, suspend flag, deferred updates and test
> feature to deoptimize objects.
>
> > In the long term, we want to get rid of suspend flags, so it's not so nice to
> introduce a new one. But I agree with Götz that it should be acceptable as
> temporary solution until async handshakes are available (which takes more
> time). So I'm ok with your change.
>
> I'm keen to build the feature on async handshakes when the arive.
>
> > You can use MutexLocker with Thread*.
>
> Done.
>
> > JVMTIDeferredUpdates: I agree with Robin. It'd be nice to move the class
> out of thread.hpp.
>
> Done.
>
> > src/hotspot/share/runtime/vframe.cpp
> > Added support for entry frame to new_vframe. Ok.
>
>
> > src/hotspot/share/runtime/vframe_hp.cpp
> > src/hotspot/share/runtime/vframe_hp.hpp
>
> > I think code()->as_nmethod() in not_global_escape_in_scope() and
> arg_escape() should better be under #ifdef ASSERT or inside the assert
> statement (no need for code cache walking in product build).
>
> Done.
>
> > jvmtiDeferredLocalVariableSet::update_monitors:
> > Please add a comment explaining that owner referenced by original info
> may be scalar replaced, but it is deoptimized in the vframe.
>
> Done.
>
> -----Original Message-----
> From: Doerr, Martin <martin.doerr at sap.com>
> Sent: Donnerstag, 12. März 2020 17:28
> To: Reingruber, Richard <richard.reingruber at sap.com>; 'Robbin Ehn'
> <robbin.ehn at oracle.com>; Lindenmaier, Goetz
> <goetz.lindenmaier at sap.com>; David Holmes <david.holmes at oracle.com>;
> Vladimir Kozlov (vladimir.kozlov at oracle.com)
> <vladimir.kozlov at oracle.com>; serviceability-dev at openjdk.java.net;
> hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-
> dev at openjdk.java.net
> Subject: RE: RFR(L) 8227745: Enable Escape Analysis for Better Performance
> in the Presence of JVMTI Agents
>
> Hi Richard,
>
>
> I managed to find time for a (almost) complete review of webrev.4. (I'll
> review the tests separately.)
>
> First of all, the change seems to be in pretty good quality for its significant
> complexity. I couldn't find any real bugs. But I'd like to propose minor
> improvements.
> I'm convinced that it's mature because we did substantial testing.
>
> I like the new functionality for object deoptimization. It can possibly be
> reused for future escape analysis based optimizations. So I appreciate having
> it available in the code base.
> In addition to that, your change makes the JVMTI implementation better
> integrated into the VM.
>
>
> Now to the details:
>
>
> src/hotspot/share/c1/c1_IR.hpp
> describe_scope parameters. Ok.
>
>
> src/hotspot/share/ci/ciEnv.cpp
> src/hotspot/share/ci/ciEnv.hpp
> Fix for JvmtiExport::can_walk_any_space() capability. Ok.
>
>
> src/hotspot/share/code/compiledMethod.cpp
> Nice cleanup!
>
>
> src/hotspot/share/code/debugInfoRec.cpp
> src/hotspot/share/code/debugInfoRec.hpp
> Additional parmeters. (Remark: I think "non_global_escape_in_scope"
> would read better than "not_global_escape_in_scope", but your version is
> consistent with existing code, so no change request from my side.) Ok.
>
>
> src/hotspot/share/code/nmethod.cpp
> Nice cleanup!
>
>
> src/hotspot/share/code/pcDesc.hpp
> Additional parameters. Ok.
>
>
> src/hotspot/share/code/scopeDesc.cpp
> src/hotspot/share/code/scopeDesc.hpp
> Improved implementation + additional parameters. Ok.
>
>
> src/hotspot/share/compiler/compileBroker.cpp
> src/hotspot/share/compiler/compileBroker.hpp
> Extra thread for DeoptimizeObjectsALot. (Remark: I would have put it into a
> follow up change together with the test in order to make this webrev
> smaller, but since it is included, I'm reviewing everything at once. Not a big
> deal.) Ok.
>
>
> src/hotspot/share/jvmci/jvmciCodeInstaller.cpp
> Additional parameters. Ok.
>
>
> src/hotspot/share/opto/c2compiler.cpp
> Make do_escape_analysis independent of JVMCI capabilities. Nice!
>
>
> src/hotspot/share/opto/callnode.hpp
> Additional fields for MachSafePointNodes. Ok.
>
>
> src/hotspot/share/opto/escape.cpp
> Annotation for MachSafePointNodes. Your added functionality looks correct.
> But I'd prefer to move the bulky code out of the large function.
> I suggest to factor out something like has_not_global_escape and
> has_arg_escape. So the code could look like this:
> SafePointNode* sfn = sfn_worklist.at(next);
> sfn->set_not_global_escape_in_scope(has_not_global_escape(sfn));
> if (sfn->is_CallJava()) {
> CallJavaNode* call = sfn->as_CallJava();
> call->set_arg_escape(has_arg_escape(call));
> }
> This would also allow us to get rid of the found_..._escape_in_args variables
> making the loops better readable.
>
> It's kind of ugly to use strcmp to recognize uncommon trap, but that seems
> to be the way to do it (there are more such places). So it's ok.
>
>
> src/hotspot/share/opto/machnode.hpp
> Additional fields for MachSafePointNodes. Ok.
>
>
> src/hotspot/share/opto/macro.cpp
> Allow elimination of non-escaping allocations. Ok.
>
>
> src/hotspot/share/opto/matcher.cpp
> src/hotspot/share/opto/output.cpp
> Copy attribute / pass parameters. Ok.
>
>
> src/hotspot/share/prims/jvmtiCodeBlobEvents.cpp
> Nice cleanup!
>
>
> src/hotspot/share/prims/jvmtiEnv.cpp
> src/hotspot/share/prims/jvmtiEnvBase.cpp
> Escape barriers + deoptimize objects for target thread. Good.
>
>
> src/hotspot/share/prims/jvmtiImpl.cpp
> src/hotspot/share/prims/jvmtiImpl.hpp
> The sequence is pretty complex:
> VM_GetOrSetLocal element initialization executes EscapeBarrier code which
> suspends the target thread (extra VM Operation).
> VM_GetOrSetLocal::doit_prologue performs object deoptimization (by VM
> Thread to prepare VM Operation with frame deoptimization).
> VM_GetOrSetLocal destructor implicitly calls EscapeBarrier destructor which
> resumes the target thread.
> But I don't have any improvement proposal. Performance is probably not a
> concern, here. So it's ok.
>
> VM_GetOrSetLocal::deoptimize_objects deoptimizes the top frame if it has
> non-globally escaping objects and other frames if they have arg escaping
> ones. Good.
>
>
> src/hotspot/share/prims/jvmtiTagMap.cpp
> Escape barriers + deoptimize objects for all threads. Ok.
>
>
> src/hotspot/share/prims/whitebox.cpp
> Added WB_IsFrameDeoptimized to API. Ok.
>
>
> src/hotspot/share/runtime/deoptimization.cpp
> Object deoptimization. I have more comments and proposals, here.
> First of all, handling recursive and waiting locks in relock_objects is tricky, but
> looks correct.
> Comments are sufficient to understand why things are done as they are
> implemented.
>
> BiasedLocking related parts are complex, but we may get rid of them in the
> future (with BiasedLocking removal).
> Anyway, looks correct, too.
>
> Typo in comment: "regularily" => "regularly"
>
> Deoptimization::fetch_unroll_info_helper is the only place where
> _jvmti_deferred_updates get deallocated (except JavaThread destructor).
> But I think we always go through it, so I can't see a memory leak or such kind
> of issues.
>
> EscapeBarrier::deoptimize_objects: ResourceMark should use
> calling_thread().
>
> You can use MutexLocker and MonitorLocker with Thread* to save the
> Thread::current() call.
>
> I'd make set_objs_are_deoptimized static and remove it from the
> EscapeBarrier interface because I think it shouldn't be used outside of
> EscapeBarrier::deoptimize_objects.
>
> Typo in comment: "we must only deoptimize" => "we only have to
> deoptimize"
>
> "bool EscapeBarrier::deoptimize_objects(intptr_t* fr_id)" is trivial and
> barrier_active() is redundant. Implementation can get moved to hpp file.
>
> I'll get back to suspend flags, later.
>
> There are weird cases regarding _self_deoptimization_in_progress.
> Assume we have 3 threads A, B and C. A deopts C, B deopts C, C deopts C. C
> can set _self_deoptimization_in_progress while A performs the handshake
> for suspending C. I think this doesn't lead to errors, but it's probably not
> desired.
> I think it would be better to use only one "wait" call in
> sync_and_suspend_one and sync_and_suspend_all.
>
> I first thought it'd be better to move ThreadBlockInVM before wait() to
> reduce thread state transitions, but that seems to be problematic because
> ThreadBlockInVM destructor contains a safepoint check which we shouldn't
> do while holding EscapeBarrier_lock. So no change request.
>
> Change in thred_added:
> I think the sequence would be more comprehensive if we waited for
> deopt_all_threads in Thread::start and all other places where a new thread
> can run into Java code (e.g. JVMTI attach).
> Your version makes new threads come up with suspend flag set. That looks
> correct, too. Advantage is that you only have to change one place
> (thread_added). It'll be interesting to see how it will look like when we use
> async handshakes instead of suspend flags.
> For now, I'm ok with your version.
>
> I'd only move MutexLocker ml(EscapeBarrier_lock...) after if (!jt-
> >is_hidden_from_external_view()).
>
> Having 4 different deoptimize_objects functions makes it a little hard to keep
> an overview of which one is used for what.
> Maybe adding suffixes would help a little bit, but I can also live with what you
> have.
> Implementation looks correct to me.
>
>
> src/hotspot/share/runtime/deoptimization.hpp
> Escape barriers and object deoptimization functions.
> Typo in comment: "helt" => "held"
>
>
> src/hotspot/share/runtime/globals.hpp
> Addition of develop flag DeoptimizeObjectsALotInterval. Ok.
>
>
> src/hotspot/share/runtime/interfaceSupport.cpp
> InterfaceSupport::deoptimizeAllObjects() is only used for
> DeoptimizeObjectsALot = 1.
> I think DeoptimizeObjectsALot = 2 is more important, but I think it's not bad
> to have DeoptimizeObjectsALot = 1 in addition. Ok.
>
>
> src/hotspot/share/runtime/interfaceSupport.inline.hpp
> Addition of deoptimizeAllObjects. Ok.
>
>
> src/hotspot/share/runtime/mutexLocker.cpp
> src/hotspot/share/runtime/mutexLocker.hpp
> Addition of EscapeBarrier_lock. Ok.
>
>
> src/hotspot/share/runtime/objectMonitor.cpp
> Make recursion count relock aware. Ok.
>
>
> src/hotspot/share/runtime/stackValue.hpp
> Better reinitilization in StackValue. Good.
>
>
> src/hotspot/share/runtime/thread.cpp
> src/hotspot/share/runtime/thread.hpp
> src/hotspot/share/runtime/thread.inline.hpp
> wait_for_object_deoptimization, suspend flag, deferred updates and test
> feature to deoptimize objects.
>
> In the long term, we want to get rid of suspend flags, so it's not so nice to
> introduce a new one. But I agree with Götz that it should be acceptable as
> temporary solution until async handshakes are available (which takes more
> time). So I'm ok with your change.
>
> You can use MutexLocker with Thread*.
>
> JVMTIDeferredUpdates: I agree with Robin. It'd be nice to move the class out
> of thread.hpp.
>
>
> src/hotspot/share/runtime/vframe.cpp
> Added support for entry frame to new_vframe. Ok.
>
>
> src/hotspot/share/runtime/vframe_hp.cpp
> src/hotspot/share/runtime/vframe_hp.hpp
>
> I think code()->as_nmethod() in not_global_escape_in_scope() and
> arg_escape() should better be under #ifdef ASSERT or inside the assert
> statement (no need for code cache walking in product build).
>
> jvmtiDeferredLocalVariableSet::update_monitors:
> Please add a comment explaining that owner referenced by original info may
> be scalar replaced, but it is deoptimized in the vframe.
>
>
> src/hotspot/share/utilities/macros.hpp
> Addition of NOT_COMPILER2_OR_JVMCI_RETURN macros. Ok.
>
>
> test/hotspot/jtreg/serviceability/jvmti/Heap/IterateHeapWithEscapeAnalysi
> sEnabled.java
> test/hotspot/jtreg/serviceability/jvmti/Heap/libIterateHeapWithEscapeAnal
> ysisEnabled.c
> New test. Will review separately.
>
>
> test/jdk/TEST.ROOT
> Addition of vm.jvmci as required property. Ok.
>
>
> test/jdk/com/sun/jdi/EATests.java
> test/jdk/com/sun/jdi/EATestsJVMCI.java
> New test. Will review separately.
>
>
> test/lib/sun/hotspot/WhiteBox.java
> Added isFrameDeoptimized to API. Ok.
>
>
> That was it. Best regards,
> Martin
>
>
> > -----Original Message-----
> > From: hotspot-compiler-dev <hotspot-compiler-dev-
> > bounces at openjdk.java.net> On Behalf Of Reingruber, Richard
> > Sent: Dienstag, 3. März 2020 21:23
> > To: 'Robbin Ehn' <robbin.ehn at oracle.com>; Lindenmaier, Goetz
> > <goetz.lindenmaier at sap.com>; David Holmes
> <david.holmes at oracle.com>;
> > Vladimir Kozlov (vladimir.kozlov at oracle.com)
> > <vladimir.kozlov at oracle.com>; serviceability-dev at openjdk.java.net;
> > hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-
> > dev at openjdk.java.net
> > Subject: RE: RFR(L) 8227745: Enable Escape Analysis for Better
> > Performance in the Presence of JVMTI Agents
> >
> > Hi Robbin,
> >
> > > > I understand that Robbin proposed to replace the usage of
> > > > _suspend_flag with handshakes. Apparently, async handshakes
> > > > are needed to do so. We have been waiting a while for removal
> > > > of the _suspend_flag / introduction of async handshakes [2].
> > > > What is the status here?
> >
> > > I have an old prototype which I would like to continue to work on.
> > > So do not assume asynch handshakes will make 15.
> > > Even if it would, I think there are a lot more investigate work to remove
> > > _suspend_flag.
> >
> > Let us know, if we can be of any help to you and be it only testing.
> >
> > > >> Full:
> > http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.4/
> >
> > > DeoptimizeObjectsALotThread is only used in compileBroker.cpp.
> > > You can move both declaration and definition to that file, no need to
> > clobber
> > > thread.[c|h]pp. (and the static function deopt_objs_alot_thread_entry)
> >
> > Will do.
> >
> > > Does JvmtiDeferredUpdates really need to be in thread.hpp, can't be in
> it's
> > own
> > > hpp file? It doesn't seem right to add JVM TI classes into thread.hpp.
> >
> > You are right. It shouldn't be declared in thread.hpp. I will look into that.
> >
> > > Note that we also think we may have a bug in deopt:
> > > https://bugs.openjdk.java.net/browse/JDK-8238237
> >
> > > I think it would be best, if possible, to push after that is resolved.
> >
> > Sure.
> >
> > > Not even nearly a full review :)
> >
> > I know :)
> >
> > Anyways, thanks a lot,
> > Richard.
> >
> >
> > -----Original Message-----
> > From: Robbin Ehn <robbin.ehn at oracle.com>
> > Sent: Monday, March 2, 2020 11:17 AM
> > To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; Reingruber,
> Richard
> > <richard.reingruber at sap.com>; David Holmes
> <david.holmes at oracle.com>;
> > Vladimir Kozlov (vladimir.kozlov at oracle.com)
> > <vladimir.kozlov at oracle.com>; serviceability-dev at openjdk.java.net;
> > hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-
> > dev at openjdk.java.net
> > Subject: Re: RFR(L) 8227745: Enable Escape Analysis for Better Performance
> > in the Presence of JVMTI Agents
> >
> > Hi,
> >
> > On 2/24/20 5:39 PM, Lindenmaier, Goetz wrote:
> > > Hi,
> > >
> > > I had a look at the progress of this change. Nothing
> > > happened since Richard posted his update using more
> > > handshakes [1].
> > > But we (SAP) would appreciate a lot if this change could
> > > be successfully reviewed and pushed.
> > >
> > > I think there is basic understanding that this
> > > change is helpful. It fixes a number of issues with JVMTI,
> > > and will deliver the same performance benefits as EA
> > > does in current production mode for debugging scenarios.
> > >
> > > This is important for us as we run our VMs prepared
> > > for debugging in production mode.
> > >
> > > I understand that Robbin proposed to replace the usage of
> > > _suspend_flag with handshakes. Apparently, async handshakes
> > > are needed to do so. We have been waiting a while for removal
> > > of the _suspend_flag / introduction of async handshakes [2].
> > > What is the status here?
> >
> > I have an old prototype which I would like to continue to work on.
> > So do not assume asynch handshakes will make 15.
> > Even if it would, I think there are a lot more investigate work to remove
> > _suspend_flag.
> >
> > >
> > > I think we should no longer wait, but proceed with
> > > this change. We will look into removing the usage of
> > > suspend_flag introduced here once it is possible to implement
> > > it with handshakes.
> >
> > Yes, sure.
> >
> > >> Full:
> http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.4/
> >
> > DeoptimizeObjectsALotThread is only used in compileBroker.cpp.
> > You can move both declaration and definition to that file, no need to
> clobber
> > thread.[c|h]pp. (and the static function deopt_objs_alot_thread_entry)
> >
> > Does JvmtiDeferredUpdates really need to be in thread.hpp, can't be in it's
> > own
> > hpp file? It doesn't seem right to add JVM TI classes into thread.hpp.
> >
> > Note that we also think we may have a bug in deopt:
> > https://bugs.openjdk.java.net/browse/JDK-8238237
> >
> > I think it would be best, if possible, to push after that is resolved.
> >
> > Not even nearly a full review :)
> >
> > Thanks, Robbin
> >
> >
> > >> Incremental:
> > >>
> http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.4.inc/
> > >>
> > >> I was not able to eliminate the additional suspend flag now. I'll take care
> > of this
> > >> as soon as the
> > >> existing suspend-resume-mechanism is reworked.
> > >>
> > >> Testing:
> > >>
> > >> Nightly tests @SAP:
> > >>
> > >> JCK and JTREG, also in Xcomp mode, SPECjvm2008, SPECjbb2015,
> > Renaissance
> > >> Suite, SAP specific tests
> > >> with fastdebug and release builds on all platforms
> > >>
> > >> Stress testing with DeoptimizeObjectsALot running SPECjvm2008 40x
> > parallel
> > >> for 24h
> > >>
> > >> Thanks, Richard.
> > >>
> > >>
> > >> More details on the changes:
> > >>
> > >> * Hide DeoptimizeObjectsALotThread from external view.
> > >>
> > >> * Changed EscapeBarrier_lock to be a _safepoint_check_never lock.
> > >> It used to be _safepoint_check_sometimes, which will be eliminated
> > sooner or
> > >> later.
> > >> I added explicit thread state changes with ThreadBlockInVM to code
> > paths
> > >> where we can wait()
> > >> on EscapeBarrier_lock to become safepoint safe.
> > >>
> > >> * Use handshake EscapeBarrierSuspendHandshake to suspend target
> > threads
> > >> instead of vm operation
> > >> VM_ThreadSuspendAllForObjDeopt.
> > >>
> > >> * Removed uses of Threads_lock. When adding a new thread we
> suspend
> > it iff
> > >> EA optimizations are
> > >> being reverted. In the previous version we were waiting on
> > Threads_lock
> > >> while EA optimizations
> > >> were reverted. See EscapeBarrier::thread_added().
> > >>
> > >> * Made tests require Xmixed compilation mode.
> > >>
> > >> * Made tests agnostic regarding tiered compilation.
> > >> I.e. tc isn't disabled anymore, and the tests can be run with tc enabled
> or
> > >> disabled.
> > >>
> > >> * Exercising EATests.java as well with stress test options
> > >> DeoptimizeObjectsALot*
> > >> Due to the non-deterministic deoptimizations some tests need to be
> > skipped.
> > >> We do this to prevent bit-rot of the stress test code.
> > >>
> > >> * Executing EATests.java as well with graal if available. Driver for this is
> > >> EATestsJVMCI.java. Graal cannot pass all tests, because it does not
> > provide all
> > >> the new debug info
> > >> (namely not_global_escape_in_scope and arg_escape in
> > scopeDesc.hpp).
> > >> And graal does not yet support the JVMTI operations force early
> return
> > and
> > >> pop frame.
> > >>
> > >> * Removed tracing from new jdi tests in EATests.java. Too much trace
> > output
> > >> before the debugging
> > >> connection is established can cause deadlock because output buffers
> fill
> > up.
> > >> (See https://bugs.openjdk.java.net/browse/JDK-8173304)
> > >>
> > >> * Many copyright year changes and smaller clean-up changes of testing
> > code
> > >> (trailing white-space and
> > >> the like).
> > >>
> > >>
> > >> -----Original Message-----
> > >> From: David Holmes <david.holmes at oracle.com>
> > >> Sent: Donnerstag, 19. Dezember 2019 03:12
> > >> To: Reingruber, Richard <richard.reingruber at sap.com>; serviceability-
> > >> dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net;
> > hotspot-
> > >> runtime-dev at openjdk.java.net; Vladimir Kozlov
> > (vladimir.kozlov at oracle.com)
> > >> <vladimir.kozlov at oracle.com>
> > >> Subject: Re: RFR(L) 8227745: Enable Escape Analysis for Better
> > Performance in
> > >> the Presence of JVMTI Agents
> > >>
> > >> Hi Richard,
> > >>
> > >> I think my issue is with the way EliminateNestedLocks works so I'm going
> > >> to look into that more deeply.
> > >>
> > >> Thanks for the explanations.
> > >>
> > >> David
> > >>
> > >> On 18/12/2019 12:47 am, Reingruber, Richard wrote:
> > >>> Hi David,
> > >>>
> > >>> > > > Some further queries/concerns:
> > >>> > > >
> > >>> > > > src/hotspot/share/runtime/objectMonitor.cpp
> > >>> > > >
> > >>> > > > Can you please explain the changes to ObjectMonitor::wait:
> > >>> > > >
> > >>> > > > ! _recursions = save // restore the old recursion count
> > >>> > > > ! + jt->get_and_reset_relock_count_after_wait(); //
> > >>> > > > increased by the deferred relock count
> > >>> > > >
> > >>> > > > what is the "deferred relock count"? I gather it relates to
> > >>> > > >
> > >>> > > > "The code was extended to be able to deoptimize objects of a
> > >>> > > frame that
> > >>> > > > is not the top frame and to let another thread than the
> owning
> > >>> > > thread do
> > >>> > > > it."
> > >>> > >
> > >>> > > Yes, these relate. Currently EA based optimizations are reverted,
> > when a
> > >> compiled frame is
> > >>> > > replaced with corresponding interpreter frames. Part of this is
> > relocking
> > >> objects with eliminated
> > >>> > > locking. New with the enhancement is that we do this also just
> > before
> > >> object references are
> > >>> > > acquired through JVMTI. In this case we deoptimize also the
> > owning
> > >> compiled frame C and we
> > >>> > > register deoptimized objects as deferred updates. When control
> > returns
> > >> to C it gets deoptimized,
> > >>> > > we notice that objects are already deoptimized (reallocated and
> > >> relocked), so we don't do it again
> > >>> > > (relocking twice would be incorrect of course). Deferred updates
> > are
> > >> copied into the new
> > >>> > > interpreter frames.
> > >>> > >
> > >>> > > Problem: relocking is not possible if the target thread T is waiting
> > on the
> > >> monitor that needs to
> > >>> > > be relocked. This happens only with non-local objects with
> > >> EliminateNestedLocks. Instead relocking
> > >>> > > is deferred until T owns the monitor again. This is what the piece
> of
> > >> code above does.
> > >>> >
> > >>> > Sorry I need some more detail here. How can you wait() on an
> > object
> > >>> > monitor if the object allocation and/or locking was optimised
> away?
> > And
> > >>> > what is a "non-local object" in this context? Isn't EA restricted to
> > >>> > thread-confined objects?
> > >>>
> > >>> "Non-local object" is an object that escapes its thread. The issue I'm
> > >> addressing with the changes
> > >>> in ObjectMonitor::wait are almost unrelated to EA. They are caused by
> > >> EliminateNestedLocks, where C2
> > >>> eliminates recursive locking of an already owned lock. The lock owning
> > object
> > >> exists on the heap, it
> > >>> is locked and you can call wait() on it.
> > >>>
> > >>> EliminateLocks is the C2 option that controls lock elimination based on
> > EA.
> > >> Both optimizations have
> > >>> in common that objects with eliminated locking need to be relocked
> > when
> > >> deoptimizing a frame,
> > >>> i.e. when replacing a compiled frame with equivalent interpreter
> > >>> frames. Deoptimization::relock_objects does that job for /all/
> eliminated
> > >> locks in scope. /All/ can
> > >>> be a mix of eliminated nested locks and locks of not-escaping objects.
> > >>>
> > >>> New with the enhancement: I call relock_objects earlier, just before
> > objects
> > >> pontentially
> > >>> escape. But then later when the owning compiled frame gets
> > deoptimized, I
> > >> must not do it again:
> > >>>
> > >>> See call to EscapeBarrier::objs_are_deoptimized in
> deoptimization.cpp:
> > >>>
> > >>> 373 if ((jvmci_enabled || ((DoEscapeAnalysis ||
> > EliminateNestedLocks) &&
> > >> EliminateLocks))
> > >>> 374 && !EscapeBarrier::objs_are_deoptimized(thread,
> > deoptee.id())) {
> > >>> 375 bool unused;
> > >>> 376 eliminate_locks(thread, chunk, realloc_failures, deoptee,
> > exec_mode,
> > >> unused);
> > >>> 377 }
> > >>>
> > >>> Now when calling relock_objects early it is quiet possible that I have to
> > relock
> > >> an object the
> > >>> target thread currently waits for. Obviously I cannot relock in this case,
> > >> instead I chose to
> > >>> introduce relock_count_after_wait to JavaThread.
> > >>>
> > >>> > Is it just that some of the locking gets optimized away e.g.
> > >>> >
> > >>> > synchronised(obj) {
> > >>> > synchronised(obj) {
> > >>> > synchronised(obj) {
> > >>> > obj.wait();
> > >>> > }
> > >>> > }
> > >>> > }
> > >>> >
> > >>> > If this is reduced to a form as-if it were a single lock of the monitor
> > >>> > (due to EA) and the wait() triggers a JVM TI event which leads to
> the
> > >>> > escape of "obj" then we need to reconstruct the true lock state,
> and
> > so
> > >>> > when the wait() internally unblocks and reacquires the monitor it
> > has to
> > >>> > set the true recursion count to 3, not the 1 that it appeared to be
> > when
> > >>> > wait() was initially called. Is that the scenario?
> > >>>
> > >>> Kind of... except that the locking is not eliminated due to EA and there
> is
> > no
> > >> JVM TI event
> > >>> triggered by wait.
> > >>>
> > >>> Add
> > >>>
> > >>> LocalObject l1 = new LocalObject();
> > >>>
> > >>> in front of the synchrnized blocks and assume a JVM TI agent acquires
> l1.
> > This
> > >> triggers the code in
> > >>> question.
> > >>>
> > >>> See that relocking/reallocating is transactional. If it is done then for
> /all/
> > >> objects in scope and it is
> > >>> done at most once. It wouldn't be quite so easy to split this in relocking
> > of
> > >> nested/EA-based
> > >>> eliminated locks.
> > >>>
> > >>> > If so I find this truly awful. Anyone using wait() in a realistic form
> > >>> > requires a notification and so the object cannot be thread
> confined.
> > In
> > >>>
> > >>> It is not thread confined.
> > >>>
> > >>> > which case I would strongly argue that upon hitting the wait() the
> > deopt
> > >>> > should occur unconditionally and so the lock state is correct before
> > we
> > >>> > wait and so we don't need to mess with the recursion count
> > internally
> > >>> > when we reacquire the monitor.
> > >>> >
> > >>> > >
> > >>> > > > which I don't like the sound of at all when it comes to
> > ObjectMonitor
> > >>> > > > state. So I'd like to understand in detail exactly what is going
> on
> > here
> > >>> > > > and why. This is a very intrusive change that seems to badly
> > break
> > >>> > > > encapsulation and impacts future changes to ObjectMonitor
> > that are
> > >> under
> > >>> > > > investigation.
> > >>> > >
> > >>> > > I would not regard this as breaking encapsulation. Certainly not
> > badly.
> > >>> > >
> > >>> > > I've added a property relock_count_after_wait to JavaThread.
> The
> > >> property is well
> > >>> > > encapsulated. Future ObjectMonitor implementations have to
> deal
> > with
> > >> recursion too. They are free
> > >>> > > in choosing a way to do that as long as that property is taken into
> > >> account. This is hardly a
> > >>> > > limitation.
> > >>> >
> > >>> > I do think this badly breaks encapsulation as you have to add a
> > callout
> > >>> > from the guts of the ObjectMonitor code to reach into the thread
> to
> > get
> > >>> > this lock count adjustment. I understand why you have had to do
> > this but
> > >>> > I would much rather see a change to the EA optimisation strategy
> so
> > that
> > >>> > this is not needed.
> > >>> >
> > >>> > > Note also that the property is a straight forward extension of the
> > >> existing concept of deferred
> > >>> > > local updates. It is embedded into the structure holding them. So
> > not
> > >> even the footprint of a
> > >>> > > JavaThread is enlarged if no deferred updates are generated.
> > >>> >
> > >>> > [...]
> > >>> >
> > >>> > >
> > >>> > > I'm actually duplicating the existing external suspend mechanism,
> > >> because a thread can be
> > >>> > > suspended at most once. And hey, and don't like that either! But
> it
> > >> seems not unlikely that the
> > >>> > > duplicate can be removed together with the original and the new
> > type
> > >> of handshakes that will be
> > >>> > > used for thread suspend can be used for object deoptimization
> > too. See
> > >> today's discussion in
> > >>> > > JDK-8227745 [2].
> > >>> >
> > >>> > I hope that discussion bears some fruit, at the moment it seems
> not
> > to
> > >>> > be possible to use handshakes here. :(
> > >>> >
> > >>> > The external suspend mechanism is a royal pain in the proverbial
> > that we
> > >>> > have to carefully live with. The idea that we're duplicating that for
> > >>> > use in another fringe area of functionality does not thrill me at all.
> > >>> >
> > >>> > To be clear, I understand the problem that exists and that you
> wish
> > to
> > >>> > solve, but for the runtime parts I balk at the complexity cost of
> > >>> > solving it.
> > >>>
> > >>> I know it's complex, but by far no rocket science.
> > >>>
> > >>> Also I find it hard to imagine another fix for JDK-8233915 besides
> > changing
> > >> the JVM TI specification.
> > >>>
> > >>> Thanks, Richard.
> > >>>
> > >>> -----Original Message-----
> > >>> From: David Holmes <david.holmes at oracle.com>
> > >>> Sent: Dienstag, 17. Dezember 2019 08:03
> > >>> To: Reingruber, Richard <richard.reingruber at sap.com>; serviceability-
> > >> dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net;
> > hotspot-
> > >> runtime-dev at openjdk.java.net; Vladimir Kozlov
> > (vladimir.kozlov at oracle.com)
> > >> <vladimir.kozlov at oracle.com>
> > >>> Subject: Re: RFR(L) 8227745: Enable Escape Analysis for Better
> > Performance
> > >> in the Presence of JVMTI Agents
> > >>>
> > >>> <resend as my mailer crashed during last send>
> > >>>
> > >>> David
> > >>>
> > >>> On 17/12/2019 4:57 pm, David Holmes wrote:
> > >>>> Hi Richard,
> > >>>>
> > >>>> On 14/12/2019 5:01 am, Reingruber, Richard wrote:
> > >>>>> Hi David,
> > >>>>>
> > >>>>> > Some further queries/concerns:
> > >>>>> >
> > >>>>> > src/hotspot/share/runtime/objectMonitor.cpp
> > >>>>> >
> > >>>>> > Can you please explain the changes to ObjectMonitor::wait:
> > >>>>> >
> > >>>>> > ! _recursions = save // restore the old recursion count
> > >>>>> > ! + jt->get_and_reset_relock_count_after_wait(); //
> > >>>>> > increased by the deferred relock count
> > >>>>> >
> > >>>>> > what is the "deferred relock count"? I gather it relates to
> > >>>>> >
> > >>>>> > "The code was extended to be able to deoptimize objects of a
> > >>>>> frame that
> > >>>>> > is not the top frame and to let another thread than the owning
> > >>>>> thread do
> > >>>>> > it."
> > >>>>>
> > >>>>> Yes, these relate. Currently EA based optimizations are reverted,
> > when
> > >>>>> a compiled frame is replaced
> > >>>>> with corresponding interpreter frames. Part of this is relocking
> > >>>>> objects with eliminated
> > >>>>> locking. New with the enhancement is that we do this also just
> before
> > >>>>> object references are acquired
> > >>>>> through JVMTI. In this case we deoptimize also the owning compiled
> > >>>>> frame C and we register
> > >>>>> deoptimized objects as deferred updates. When control returns to
> C
> > it
> > >>>>> gets deoptimized, we notice
> > >>>>> that objects are already deoptimized (reallocated and relocked), so
> > we
> > >>>>> don't do it again (relocking
> > >>>>> twice would be incorrect of course). Deferred updates are copied
> into
> > >>>>> the new interpreter frames.
> > >>>>>
> > >>>>> Problem: relocking is not possible if the target thread T is waiting
> > >>>>> on the monitor that needs to be
> > >>>>> relocked. This happens only with non-local objects with
> > >>>>> EliminateNestedLocks. Instead relocking is
> > >>>>> deferred until T owns the monitor again. This is what the piece of
> > >>>>> code above does.
> > >>>>
> > >>>> Sorry I need some more detail here. How can you wait() on an object
> > >>>> monitor if the object allocation and/or locking was optimised away?
> > And
> > >>>> what is a "non-local object" in this context? Isn't EA restricted to
> > >>>> thread-confined objects?
> > >>>>
> > >>>> Is it just that some of the locking gets optimized away e.g.
> > >>>>
> > >>>> synchronised(obj) {
> > >>>> synchronised(obj) {
> > >>>> synchronised(obj) {
> > >>>> obj.wait();
> > >>>> }
> > >>>> }
> > >>>> }
> > >>>>
> > >>>> If this is reduced to a form as-if it were a single lock of the monitor
> > >>>> (due to EA) and the wait() triggers a JVM TI event which leads to the
> > >>>> escape of "obj" then we need to reconstruct the true lock state, and
> so
> > >>>> when the wait() internally unblocks and reacquires the monitor it has
> to
> > >>>> set the true recursion count to 3, not the 1 that it appeared to be
> when
> > >>>> wait() was initially called. Is that the scenario?
> > >>>>
> > >>>> If so I find this truly awful. Anyone using wait() in a realistic form
> > >>>> requires a notification and so the object cannot be thread confined.
> In
> > >>>> which case I would strongly argue that upon hitting the wait() the
> > deopt
> > >>>> should occur unconditionally and so the lock state is correct before
> we
> > >>>> wait and so we don't need to mess with the recursion count internally
> > >>>> when we reacquire the monitor.
> > >>>>
> > >>>>>
> > >>>>> > which I don't like the sound of at all when it comes to
> > >>>>> ObjectMonitor
> > >>>>> > state. So I'd like to understand in detail exactly what is going
> > >>>>> on here
> > >>>>> > and why. This is a very intrusive change that seems to badly
> > break
> > >>>>> > encapsulation and impacts future changes to ObjectMonitor
> that
> > >>>>> are under
> > >>>>> > investigation.
> > >>>>>
> > >>>>> I would not regard this as breaking encapsulation. Certainly not
> badly.
> > >>>>>
> > >>>>> I've added a property relock_count_after_wait to JavaThread. The
> > >>>>> property is well
> > >>>>> encapsulated. Future ObjectMonitor implementations have to deal
> > with
> > >>>>> recursion too. They are free in
> > >>>>> choosing a way to do that as long as that property is taken into
> > >>>>> account. This is hardly a
> > >>>>> limitation.
> > >>>>
> > >>>> I do think this badly breaks encapsulation as you have to add a callout
> > >>>> from the guts of the ObjectMonitor code to reach into the thread to
> > get
> > >>>> this lock count adjustment. I understand why you have had to do this
> > but
> > >>>> I would much rather see a change to the EA optimisation strategy so
> > that
> > >>>> this is not needed.
> > >>>>
> > >>>>> Note also that the property is a straight forward extension of the
> > >>>>> existing concept of deferred
> > >>>>> local updates. It is embedded into the structure holding them. So
> not
> > >>>>> even the footprint of a
> > >>>>> JavaThread is enlarged if no deferred updates are generated.
> > >>>>>
> > >>>>> > ---
> > >>>>> >
> > >>>>> > src/hotspot/share/runtime/thread.cpp
> > >>>>> >
> > >>>>> > Can you please explain why
> > >>>>> JavaThread::wait_for_object_deoptimization
> > >>>>> > has to be handcrafted in this way rather than using proper
> > >>>>> transitions.
> > >>>>> >
> > >>>>>
> > >>>>> I wrote wait_for_object_deoptimization taking
> > >>>>> JavaThread::java_suspend_self_with_safepoint_check
> > >>>>> as template. So in short: for the same reasons :)
> > >>>>>
> > >>>>> Threads reach both methods as part of thread state transitions,
> > >>>>> therefore special handling is
> > >>>>> required to change thread state on top of ongoing transitions.
> > >>>>>
> > >>>>> > We got rid of "deopt suspend" some time ago and it is
> disturbing
> > >>>>> to see
> > >>>>> > it being added back (effectively). This seems like it may be
> > >>>>> something
> > >>>>> > that handshakes could be used for.
> > >>>>>
> > >>>>> Deopt suspend used to be something rather different with a similar
> > >>>>> name[1]. It is not being added back.
> > >>>>
> > >>>> I stand corrected. Despite comments in the code to the contrary
> > >>>> deopt_suspend didn't actually cause a self-suspend. I was doing a lot
> of
> > >>>> cleanup in this area 13 years ago :)
> > >>>>
> > >>>>>
> > >>>>> I'm actually duplicating the existing external suspend mechanism,
> > >>>>> because a thread can be suspended
> > >>>>> at most once. And hey, and don't like that either! But it seems not
> > >>>>> unlikely that the duplicate can
> > >>>>> be removed together with the original and the new type of
> > handshakes
> > >>>>> that will be used for
> > >>>>> thread suspend can be used for object deoptimization too. See
> > today's
> > >>>>> discussion in JDK-8227745 [2].
> > >>>>
> > >>>> I hope that discussion bears some fruit, at the moment it seems not
> to
> > >>>> be possible to use handshakes here. :(
> > >>>>
> > >>>> The external suspend mechanism is a royal pain in the proverbial that
> > we
> > >>>> have to carefully live with. The idea that we're duplicating that for
> > >>>> use in another fringe area of functionality does not thrill me at all.
> > >>>>
> > >>>> To be clear, I understand the problem that exists and that you wish to
> > >>>> solve, but for the runtime parts I balk at the complexity cost of
> > >>>> solving it.
> > >>>>
> > >>>> Thanks,
> > >>>> David
> > >>>> -----
> > >>>>
> > >>>>> Thanks, Richard.
> > >>>>>
> > >>>>> [1] Deopt suspend was something like an async. handshake for
> > >>>>> architectures with register windows,
> > >>>>> where patching the return pc for deoptimization of a compiled
> > >>>>> frame was racy if the owner thread
> > >>>>> was in native code. Instead a "deopt" suspend flag was set on
> > >>>>> which the thread patched its own
> > >>>>> frame upon return from native. So no thread was suspended. It
> > got
> > >>>>> its name only from the name of
> > >>>>> the flags.
> > >>>>>
> > >>>>> [2] Discussion about using handshakes to sync. with the target
> thread:
> > >>>>>
> > >>>>> https://bugs.openjdk.java.net/browse/JDK-
> > >>
> >
> 8227745?focusedCommentId=14306727&page=com.atlassian.jira.plugin.syst
> > e
> > >> m.issuetabpanels:comment-tabpanel#comment-14306727
> > >>>>>
> > >>>>>
> > >>>>> -----Original Message-----
> > >>>>> From: David Holmes <david.holmes at oracle.com>
> > >>>>> Sent: Freitag, 13. Dezember 2019 00:56
> > >>>>> To: Reingruber, Richard <richard.reingruber at sap.com>;
> > >>>>> serviceability-dev at openjdk.java.net;
> > >>>>> hotspot-compiler-dev at openjdk.java.net;
> > >>>>> hotspot-runtime-dev at openjdk.java.net
> > >>>>> Subject: Re: RFR(L) 8227745: Enable Escape Analysis for Better
> > >>>>> Performance in the Presence of JVMTI Agents
> > >>>>>
> > >>>>> Hi Richard,
> > >>>>>
> > >>>>> Some further queries/concerns:
> > >>>>>
> > >>>>> src/hotspot/share/runtime/objectMonitor.cpp
> > >>>>>
> > >>>>> Can you please explain the changes to ObjectMonitor::wait:
> > >>>>>
> > >>>>> ! _recursions = save // restore the old recursion count
> > >>>>> ! + jt->get_and_reset_relock_count_after_wait(); //
> > >>>>> increased by the deferred relock count
> > >>>>>
> > >>>>> what is the "deferred relock count"? I gather it relates to
> > >>>>>
> > >>>>> "The code was extended to be able to deoptimize objects of a
> frame
> > that
> > >>>>> is not the top frame and to let another thread than the owning
> thread
> > do
> > >>>>> it."
> > >>>>>
> > >>>>> which I don't like the sound of at all when it comes to ObjectMonitor
> > >>>>> state. So I'd like to understand in detail exactly what is going on here
> > >>>>> and why. This is a very intrusive change that seems to badly break
> > >>>>> encapsulation and impacts future changes to ObjectMonitor that
> are
> > under
> > >>>>> investigation.
> > >>>>>
> > >>>>> ---
> > >>>>>
> > >>>>> src/hotspot/share/runtime/thread.cpp
> > >>>>>
> > >>>>> Can you please explain why
> > JavaThread::wait_for_object_deoptimization
> > >>>>> has to be handcrafted in this way rather than using proper
> transitions.
> > >>>>>
> > >>>>> We got rid of "deopt suspend" some time ago and it is disturbing to
> > see
> > >>>>> it being added back (effectively). This seems like it may be
> something
> > >>>>> that handshakes could be used for.
> > >>>>>
> > >>>>> Thanks,
> > >>>>> David
> > >>>>> -----
> > >>>>>
> > >>>>> On 12/12/2019 7:02 am, David Holmes wrote:
> > >>>>>> On 12/12/2019 1:07 am, Reingruber, Richard wrote:
> > >>>>>>> Hi David,
> > >>>>>>>
> > >>>>>>> > Most of the details here are in areas I can comment on in
> > detail,
> > >>>>>>> but I
> > >>>>>>> > did take an initial general look at things.
> > >>>>>>>
> > >>>>>>> Thanks for taking the time!
> > >>>>>>
> > >>>>>> Apologies the above should read:
> > >>>>>>
> > >>>>>> "Most of the details here are in areas I *can't* comment on in
> detail
> > >>>>>> ..."
> > >>>>>>
> > >>>>>> David
> > >>>>>>
> > >>>>>>> > The only thing that jumped out at me is that I think the
> > >>>>>>> > DeoptimizeObjectsALotThread should be a hidden thread.
> > >>>>>>> >
> > >>>>>>> > + bool is_hidden_from_external_view() const { return true;
> }
> > >>>>>>>
> > >>>>>>> Yes, it should. Will add the method like above.
> > >>>>>>>
> > >>>>>>> > Also I don't see any testing of the
> > DeoptimizeObjectsALotThread.
> > >>>>>>> Without
> > >>>>>>> > active testing this will just bit-rot.
> > >>>>>>>
> > >>>>>>> DeoptimizeObjectsALot is meant for stress testing with a larger
> > >>>>>>> workload. I will add a minimal test
> > >>>>>>> to keep it fresh.
> > >>>>>>>
> > >>>>>>> > Also on the tests I don't understand your @requires clause:
> > >>>>>>> >
> > >>>>>>> > @requires ((vm.compMode != "Xcomp") &
> > vm.compiler2.enabled
> > >> &
> > >>>>>>> > (vm.opt.TieredCompilation != true))
> > >>>>>>> >
> > >>>>>>> > This seems to require that TieredCompilation is disabled, but
> > >>>>>>> tiered is
> > >>>>>>> > our normal mode of operation. ??
> > >>>>>>> >
> > >>>>>>>
> > >>>>>>> I removed the clause. I guess I wanted to target the tests towards
> > the
> > >>>>>>> code they are supposed to
> > >>>>>>> test, and it's easier to analyze failures w/o tiered compilation and
> > >>>>>>> with just one compiler thread.
> > >>>>>>>
> > >>>>>>> Additionally I will make use of
> > >>>>>>> compiler.whitebox.CompilerWhiteBoxTest.THRESHOLD in the
> tests.
> > >>>>>>>
> > >>>>>>> Thanks,
> > >>>>>>> Richard.
> > >>>>>>>
> > >>>>>>> -----Original Message-----
> > >>>>>>> From: David Holmes <david.holmes at oracle.com>
> > >>>>>>> Sent: Mittwoch, 11. Dezember 2019 08:03
> > >>>>>>> To: Reingruber, Richard <richard.reingruber at sap.com>;
> > >>>>>>> serviceability-dev at openjdk.java.net;
> > >>>>>>> hotspot-compiler-dev at openjdk.java.net;
> > >>>>>>> hotspot-runtime-dev at openjdk.java.net
> > >>>>>>> Subject: Re: RFR(L) 8227745: Enable Escape Analysis for Better
> > >>>>>>> Performance in the Presence of JVMTI Agents
> > >>>>>>>
> > >>>>>>> Hi Richard,
> > >>>>>>>
> > >>>>>>> On 11/12/2019 7:45 am, Reingruber, Richard wrote:
> > >>>>>>>> Hi,
> > >>>>>>>>
> > >>>>>>>> I would like to get reviews please for
> > >>>>>>>>
> > >>>>>>>>
> > http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.3/
> > >>>>>>>>
> > >>>>>>>> Corresponding RFE:
> > >>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8227745
> > >>>>>>>>
> > >>>>>>>> Fixes also https://bugs.openjdk.java.net/browse/JDK-8233915
> > >>>>>>>> And potentially https://bugs.openjdk.java.net/browse/JDK-
> > 8214584 [1]
> > >>>>>>>>
> > >>>>>>>> Vladimir Kozlov kindly put webrev.3 through tier1-8 testing
> > without
> > >>>>>>>> issues (thanks!). In addition the
> > >>>>>>>> change is being tested at SAP since I posted the first RFR some
> > >>>>>>>> months ago.
> > >>>>>>>>
> > >>>>>>>> The intention of this enhancement is to benefit performance
> wise
> > from
> > >>>>>>>> escape analysis even if JVMTI
> > >>>>>>>> agents request capabilities that allow them to access local
> variable
> > >>>>>>>> values. E.g. if you start-up
> > >>>>>>>> with -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,
> > then
> > >>>>>>>> escape analysis is disabled right
> > >>>>>>>> from the beginning, well before a debugger attaches -- if ever
> one
> > >>>>>>>> should do so. With the
> > >>>>>>>> enhancement, escape analysis will remain enabled until and
> after
> > a
> > >>>>>>>> debugger attaches. EA based
> > >>>>>>>> optimizations are reverted just before an agent acquires the
> > >>>>>>>> reference to an object. In the JBS item
> > >>>>>>>> you'll find more details.
> > >>>>>>>
> > >>>>>>> Most of the details here are in areas I can comment on in detail,
> but
> > I
> > >>>>>>> did take an initial general look at things.
> > >>>>>>>
> > >>>>>>> The only thing that jumped out at me is that I think the
> > >>>>>>> DeoptimizeObjectsALotThread should be a hidden thread.
> > >>>>>>>
> > >>>>>>> + bool is_hidden_from_external_view() const { return true; }
> > >>>>>>>
> > >>>>>>> Also I don't see any testing of the DeoptimizeObjectsALotThread.
> > >>>>>>> Without
> > >>>>>>> active testing this will just bit-rot.
> > >>>>>>>
> > >>>>>>> Also on the tests I don't understand your @requires clause:
> > >>>>>>>
> > >>>>>>> @requires ((vm.compMode != "Xcomp") &
> > vm.compiler2.enabled &
> > >>>>>>> (vm.opt.TieredCompilation != true))
> > >>>>>>>
> > >>>>>>> This seems to require that TieredCompilation is disabled, but
> tiered
> > is
> > >>>>>>> our normal mode of operation. ??
> > >>>>>>>
> > >>>>>>> Thanks,
> > >>>>>>> David
> > >>>>>>>
> > >>>>>>>> Thanks,
> > >>>>>>>> Richard.
> > >>>>>>>>
> > >>>>>>>> [1] Experimental fix for JDK-8214584 based on JDK-8227745
> > >>>>>>>>
> > >>
> >
> http://cr.openjdk.java.net/~rrich/webrevs/2019/8214584/experiment_v1.pa
> > tc
> > >> h
> > >>>>>>>>
> > >>>>>>>>
> > >>>>>>>>
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