RFR(L) 8153224 Monitor deflation prolong safepoints (CR5/v2.05/8-for-jdk13)
Daniel D. Daugherty
daniel.daugherty at oracle.com
Thu Jul 11 19:49:11 UTC 2019
Greetings,
I've been focused on chasing down and fixing the rare test failures
that only pop up rarely. So this round is primarily fixes for races
with a few additional fixes that came from Karen's review of CR4.
Thanks Karen!
I have attached the list of fixes from CR4 to CR5 instead of putting
in the main body of this email.
Main bug URL:
JDK-8153224 Monitor deflation prolong safepoints
https://bugs.openjdk.java.net/browse/JDK-8153224
The project is currently baselined on jdk-13+29. This will likely be
the last JDK13 baseline for this project and I'll roll to the JDK14
(jdk/jdk) repo soon...
Here's the full webrev URL:
http://cr.openjdk.java.net/~dcubed/8153224-webrev/8-for-jdk13.full/
Here's the incremental webrev URL:
http://cr.openjdk.java.net/~dcubed/8153224-webrev/8-for-jdk13.inc/
I have not yet checked the OpenJDK wiki to see if it needs any updates
to match the CR5 changes:
https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation
(I did update the OpenJDK wiki for the CR4 changes back on 2019.06.26)
This version of the patch has been thru Mach5 tier[1-3] testing on
Oracle's usual set of platforms. Mach5 tier[4-6] is running now and
Mach5 tier[78] will follow. I'll kick off the usual stress testing
on Linux-X64, macOSX and Solaris-X64 as those machines become available.
Since I haven't made any performance changes in this round, I'll only
be running SPECjbb2015 to gather the latest monitorinflation logs.
Next up:
- We're still seeing 4-5% lower performance with SPECjbb2015 on
Linux-X64 and we've determined that some of that comes from
contention on the gListLock. So I'm going to investigate removing
the gListLock. Yes, another lock free set of changes is coming!
- Of course, going lock free often causes new races and new failures
so that's a good reason for make those changes isolated in their
own round (and not holding up CR5/v2.05/8-for-jdk13 anymore).
- I finally have a potential fix for the Win* failure with
gc/g1/humongousObjects/TestHumongousClassLoader.java
but I haven't run it through Mach5 yet so it'll be in the next round.
- Some RTM tests were recently re-enabled in Mach5 and I'm seeing some
monitor related failures there. I suspect that I need to go take a
look at the C2 RTM macro assembler code and look for things that might
conflict if Async Monitor Deflation. If you're interested in that kind
of issue, then see the macroAssembler_x86.cpp sanity check that I
added in this round!
Thanks, in advance, for any questions, comments or suggestions.
Dan
On 5/26/19 8:30 PM, Daniel D. Daugherty wrote:
> Greetings,
>
> I have a fix for an issue that came up during performance testing.
> Many thanks to Robbin for diagnosing the issue in his SPECjbb2015
> experiments.
>
> Here's the list of changes from CR3 to CR4. The list is a bit
> verbose due to the complexity of the issue, but the changes
> themselves are not that big.
>
> Functional:
> - Change SafepointSynchronize::is_cleanup_needed() from calling
> ObjectSynchronizer::is_cleanup_needed() to calling
> ObjectSynchronizer::is_safepoint_deflation_needed():
> - is_safepoint_deflation_needed() returns the result of
> monitors_used_above_threshold() for safepoint based
> monitor deflation (!AsyncDeflateIdleMonitors).
> - For AsyncDeflateIdleMonitors, it only returns true if
> there is a special deflation request, e.g., System.gc()
> - This solves a bug where there are a bunch of Cleanup
> safepoints that simply request async deflation which
> keeps the async JavaThreads from making progress on
> their async deflation work.
> - Add AsyncDeflationInterval diagnostic option. Description:
> Async deflate idle monitors every so many milliseconds when
> MonitorUsedDeflationThreshold is exceeded (0 is off).
> - Replace ObjectSynchronizer::gOmShouldDeflateIdleMonitors() with
> ObjectSynchronizer::is_async_deflation_needed():
> - is_async_deflation_needed() returns true when
> is_async_cleanup_requested() is true or when
> monitors_used_above_threshold() is true (but no more often than
> AsyncDeflationInterval).
> - if AsyncDeflateIdleMonitors Service_lock->wait() now waits for
> at most GuaranteedSafepointInterval millis:
> - This allows is_async_deflation_needed() to be checked at
> the same interval as GuaranteedSafepointInterval.
> (default is 1000 millis/1 second)
> - Once is_async_deflation_needed() has returned true, it
> generally cannot return true for AsyncDeflationInterval.
> This is to prevent async deflation from swamping the
> ServiceThread.
> - The ServiceThread still handles async deflation of the global
> in-use list and now it also marks JavaThreads for async deflation
> of their in-use lists.
> - The ServiceThread will check for async deflation work every
> GuaranteedSafepointInterval.
> - A safepoint can still cause the ServiceThread to check for
> async deflation work via is_async_deflation_requested.
> - Refactor code from ObjectSynchronizer::is_cleanup_needed() into
> monitors_used_above_threshold() and remove is_cleanup_needed().
> - In addition to System.gc(), the VM_Exit VM op and the final
> VMThread safepoint now set the is_special_deflation_requested
> flag to reduce the in-use monitor population that is reported by
> ObjectSynchronizer::log_in_use_monitor_details() at VM exit.
>
> Test update:
> - test/hotspot/gtest/oops/test_markOop.cpp is updated to work with
> AsyncDeflateIdleMonitors.
>
> Collateral:
> - Add/clarify/update some logging messages.
>
> Cleanup:
> - Updated comments based on Karen's code review.
> - Change 'special cleanup' -> 'special deflation' and
> 'async cleanup' -> 'async deflation'.
> - comment and function name changes
> - Clarify MonitorUsedDeflationThreshold description;
>
>
> Main bug URL:
>
> JDK-8153224 Monitor deflation prolong safepoints
> https://bugs.openjdk.java.net/browse/JDK-8153224
>
> The project is currently baselined on jdk-13+22.
>
> Here's the full webrev URL:
>
> http://cr.openjdk.java.net/~dcubed/8153224-webrev/7-for-jdk13.full/
>
> Here's the incremental webrev URL:
>
> http://cr.openjdk.java.net/~dcubed/8153224-webrev/7-for-jdk13.inc/
>
> I have not updated the OpenJDK wiki to reflect the CR4 changes:
>
> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation
>
> The wiki doesn't say a whole lot about the async deflation invocation
> mechanism so I have to figure out how to add that content.
>
> This version of the patch has been thru Mach5 tier[1-8] testing on
> Oracle's usual set of platforms. My Solaris-X64 stress kit run is
> running now. Kitchensink8H on product, fastdebug, and slowdebug bits
> are running on Linux-X64, MacOSX and Solaris-X64. I still have to run
> my stress kit on Linux-X64. I still have to run the SPECjbb2015
> baseline and CR4 runs on Linux-X64, MacOSX and Solaris-X64.
>
> Thanks, in advance, for any questions, comments or suggestions.
>
> Dan
>
> On 5/6/19 11:52 AM, Daniel D. Daugherty wrote:
>> Greetings,
>>
>> I had some discussions with Karen about a race that was in the
>> ObjectMonitor::enter() code in CR2/v2.02/5-for-jdk13. This race was
>> theoretical and I had no test failures due to it. The fix is pretty
>> simple: remove the special case code for async deflation in the
>> ObjectMonitor::enter() function and rely solely on the ref_count
>> for ObjectMonitor::enter() protection.
>>
>> During those discussions Karen also floated the idea of using the
>> ref_count field instead of the contentions field for the Async
>> Monitor Deflation protocol. I decided to go ahead and code up that
>> change and I have run it through the usual stress and Mach5 testing
>> with no issues. It's also known as v2.03 (for those for with the
>> patches) and as webrev/6-for-jdk13 (for those with webrev URLs).
>> Sorry for all the names...
>>
>> Main bug URL:
>>
>> JDK-8153224 Monitor deflation prolong safepoints
>> https://bugs.openjdk.java.net/browse/JDK-8153224
>>
>> The project is currently baselined on jdk-13+18.
>>
>> Here's the full webrev URL:
>>
>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/6-for-jdk13.full/
>>
>> Here's the incremental webrev URL:
>>
>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/6-for-jdk13.inc/
>>
>> I have also updated the OpenJDK wiki to reflect the CR3 changes:
>>
>> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation
>>
>> This version of the patch has been thru Mach5 tier[1-8] testing on
>> Oracle's usual set of platforms. My Solaris-X64 stress kit run had
>> no issues. Kitchensink8H on product, fastdebug, and slowdebug bits
>> had no failures on Linux-X64; MacOSX fastdebug and slowdebug and
>> Solaris-X64 release had the usual "Too large time diff" complaints.
>> 12 hour Inflate2 runs on product, fastdebug and slowdebug bits on
>> Linux-X64, MacOSX and Solaris-X64 had no failures. My Linux-X64
>> stress kit is running right now.
>>
>> I've done the SPECjbb2015 baseline and CR3 runs. I need to gather
>> the results and analyze them.
>>
>> Thanks, in advance, for any questions, comments or suggestions.
>>
>> Dan
>>
>>
>> On 4/25/19 12:38 PM, Daniel D. Daugherty wrote:
>>> Greetings,
>>>
>>> I have a small but important bug fix for the Async Monitor Deflation
>>> project ready to go. It's also known as v2.02 (for those for with the
>>> patches) and as webrev/5-for-jdk13 (for those with webrev URLs). Sorry
>>> for all the names...
>>>
>>> JDK-8222295 was pushed to jdk/jdk two days ago so that baseline patch
>>> is out of our hair.
>>>
>>> Main bug URL:
>>>
>>> JDK-8153224 Monitor deflation prolong safepoints
>>> https://bugs.openjdk.java.net/browse/JDK-8153224
>>>
>>> The project is currently baselined on jdk-13+17.
>>>
>>> Here's the full webrev URL:
>>>
>>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/5-for-jdk13.full/
>>>
>>> Here's the incremental webrev URL (JDK-8153224):
>>>
>>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/5-for-jdk13.inc/
>>>
>>> I still have to update the OpenJDK wiki to reflect the CR2 changes:
>>>
>>> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation
>>>
>>> This version of the patch has been thru Mach5 tier[1-6] testing on
>>> Oracle's usual set of platforms. Mach5 tier[7-8] is running now.
>>> My stress kit is running on Solaris-X64 now. Kitchensink8H is running
>>> now on product, fastdebug, and slowdebug bits on Linux-X64, MacOSX
>>> and Solaris-X64. 12 hour Inflate2 runs are running now on product,
>>> fastdebug and slowdebug bits on Linux-X64, MacOSX and Solaris-X64.
>>> I'll start my my stress kit on Linux-X64 sometime on Sunday (after
>>> my jdk-13+18 stress run is done).
>>>
>>> I'll do SPECjbb2015 baseline and CR2 runs after all the stress
>>> testing is done.
>>>
>>> Thanks, in advance, for any questions, comments or suggestions.
>>>
>>> Dan
>>>
>>>
>>> On 4/19/19 11:58 AM, Daniel D. Daugherty wrote:
>>>> Greetings,
>>>>
>>>> I finally have CR1 for the Async Monitor Deflation project ready to
>>>> go. It's also known as v2.01 (for those for with the patches) and as
>>>> webrev/4-for-jdk13 (for those with webrev URLs). Sorry for all the
>>>> names...
>>>>
>>>> Main bug URL:
>>>>
>>>> JDK-8153224 Monitor deflation prolong safepoints
>>>> https://bugs.openjdk.java.net/browse/JDK-8153224
>>>>
>>>> Baseline bug fixes URL:
>>>>
>>>> JDK-8222295 more baseline cleanups from Async Monitor Deflation
>>>> project
>>>> https://bugs.openjdk.java.net/browse/JDK-8222295
>>>>
>>>> The project is currently baselined on jdk-13+15.
>>>>
>>>> Here's the webrev for the latest baseline changes (JDK-8222295):
>>>>
>>>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/4-for-jdk13.8222295
>>>>
>>>> Here's the full webrev URL (JDK-8153224 only):
>>>>
>>>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/4-for-jdk13.full/
>>>>
>>>> Here's the incremental webrev URL (JDK-8153224):
>>>>
>>>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/4-for-jdk13.inc/
>>>>
>>>> So I'm looking for reviews for both JDK-8222295 and the latest version
>>>> of JDK-8153224...
>>>>
>>>> I still have to update the OpenJDK wiki to reflect the CR changes:
>>>>
>>>> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation
>>>>
>>>> This version of the patch has been thru Mach5 tier[1-3] testing on
>>>> Oracle's usual set of platforms. Mach5 tier[4-6] is running now and
>>>> Mach5 tier[78] will be run later today. My stress kit on Solaris-X64
>>>> is running now. Linux-X64 stress testing will start on Sunday. I'm
>>>> planning to do Kitchensink runs, SPECjbb2015 runs and my monitor
>>>> inflation stress tests on Linux-X64, MacOSX and Solaris-X64.
>>>>
>>>> Thanks, in advance, for any questions, comments or suggestions.
>>>>
>>>> Dan
>>>>
>>>>
>>>> On 3/24/19 9:57 AM, Daniel D. Daugherty wrote:
>>>>> Greetings,
>>>>>
>>>>> Welcome to the OpenJDK review thread for my port of Carsten's work
>>>>> on:
>>>>>
>>>>> JDK-8153224 Monitor deflation prolong safepoints
>>>>> https://bugs.openjdk.java.net/browse/JDK-8153224
>>>>>
>>>>> Here's a link to the OpenJDK wiki that describes my port:
>>>>>
>>>>> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation
>>>>>
>>>>> Here's the webrev URL:
>>>>>
>>>>> http://cr.openjdk.java.net/~dcubed/8153224-webrev/3-for-jdk13/
>>>>>
>>>>> Here's a link to Carsten's original webrev:
>>>>>
>>>>> http://cr.openjdk.java.net/~cvarming/monitor_deflate_conc/0/
>>>>>
>>>>> Earlier versions of this patch have been through several rounds of
>>>>> preliminary review. Many thanks to Carsten, Coleen, Robbin, and
>>>>> Roman for their preliminary code review comments. A very special
>>>>> thanks to Robbin and Roman for building and testing the patch in
>>>>> their own environments (including specJBB2015).
>>>>>
>>>>> This version of the patch has been thru Mach5 tier[1-8] testing on
>>>>> Oracle's usual set of platforms. Earlier versions have been run
>>>>> through my stress kit on my Linux-X64 and Solaris-X64 servers
>>>>> (product, fastdebug, slowdebug).Earlier versions have run Kitchensink
>>>>> for 12 hours on MacOSX, Linux-X64 and Solaris-X64 (product, fastdebug
>>>>> and slowdebug). Earlier versions have run my monitor inflation stress
>>>>> tests for 12 hours on MacOSX, Linux-X64 and Solaris-X64 (product,
>>>>> fastdebug and slowdebug).
>>>>>
>>>>> All of the testing done on earlier versions will be redone on the
>>>>> latest version of the patch.
>>>>>
>>>>> Thanks, in advance, for any questions, comments or suggestions.
>>>>>
>>>>> Dan
>>>>>
>>>>> P.S.
>>>>> One subtest in gc/g1/humongousObjects/TestHumongousClassLoader.java
>>>>> is currently failing in -Xcomp mode on Win* only. I've been trying
>>>>> to characterize/analyze this failure for more than a week now. At
>>>>> this point I'm convinced that Async Monitor Deflation is aggravating
>>>>> an existing bug. However, I plan to have a better handle on that
>>>>> failure before these bits are pushed to the jdk/jdk repo.
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>
-------------- next part --------------
Functional:
- Add sanity check to MacroAssembler::fast_lock() to verify that
the ObjectMonitor's object field still refers to the object
that we have just locked with the C2 fast enter optimization.
- Replace raw references to _ref_count to ref_count() to see the
proper version of the value. Fixed rare racy assert() and
guarantee() failures.
- Add ObjectMonitor::owner_is_DEFLATER_MARKER() accessor to do
proper load_acquire of the owner field.
- Update ObjectMonitorHandle::save_om_ptr() and ObjectSynchronizer::
deflate_monitor_using_JT() to use owner_is_DEFLATER_MARKER().
Fixed racy guarantee() failures.
- Allow the owner == DEFLATER_MARKER value to linger until a
deflated ObjectMonitor is reused for an enter operation. This
prevents the C2 ObjectMonitor enter optimization from racing
with async deflation. Fixed rare "Non-balanced monitor enter/exit!"
assertion failures.
- Add/redo fast path for acquiring an ObjectMonitor that only went
thru the first part of the Async Deflation protocol to:
ObjectMonitor::enter(add), ObjectMonitor::EnterI(redo * 2),
ObjectMonitor::ReenterI(redo), ObjectSynchronizer::quick_enter(add)
Yes, this also handles the lingering owner == DEFLATER_MARKER
value.
- ObjectSynchronizer::deflate_monitor() needs to check
ref_count() in order to not deflate ObjectMonitor* that
are in use across a safepoint. Fixed rare racy assert()
and guarantee failures.
- ObjectSynchronizer::deflate_monitor() can clear a lingering
owner == DEFLATER_MARKER value because the C2 ObjectMonitor
enter optimization race cannot happen over a safepoint.
Test update:
- None this round.
Collateral:
- None this round.
Cleanup:
- Add comments requested by Karen in her CR4 code review.
- VM_Exit::doit_prologue() and the regular VM exit path should only
make a special deflation request if we have logging enabled.
Karen, thanks for catching this!
- Merge ObjectMonitor::is_busy() and ObjectMonitor::is_busy_async()
into just is_busy().
- Update is_busy_to_string() to do selective output of the owner
field: DEFLATER_MARKER value is not shown as a busy value.
- Refactor MonitorBound option check into is_MonitorBound_exceeded()
and add support to ObjectSynchronizer::is_async_deflation_needed();
existing MonitorBound code in omAlloc() including InduceScavenge()
now uses is_MonitorBound_exceeded() and is not used when
AsyncDeflateIdleMonitors == true.
- ObjectMonitor::dec_ref_count() and ObjectMonitor::inc_ref_count()
should use ADIM_guarantee() instead of guarantee().
- Add and clarify various comments.
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