RFR JDK-8232222: Set state to 'linked' when an archived class is restored at runtime
Jiangli Zhou
jianglizhou at google.com
Thu May 28 01:17:40 UTC 2020
On Wed, May 27, 2020 at 1:56 PM Ioi Lam <ioi.lam at oracle.com> wrote:
>
> On 5/26/20 6:21 PM, Jiangli Zhou wrote:
>
> > Focusing on the link state for archived classes in this thread, I
> > updated the webrev to only set archived boot classes to 'linked' state
> > at restore time. More investigations can be done for archived classes
> > for other builtin loaders.
> >
> > https://bugs.openjdk.java.net/browse/JDK-8232222
> > http://cr.openjdk.java.net/~jiangli/8232222/webrev.02/
> >
> > Please let me know if there is any additional concerns to the change.
> >
> > Best regards,
> > Jiangli
> >
> Hi Jiangli,
>
> I think the change is fine. I am wondering if this
>
> 2530 if (!BytecodeVerificationLocal &&
> 2531 loader_data->is_the_null_class_loader_data()) {
> 2532 _init_state = linked;
> 2533 }
>
>
> can be changed to
>
> if (!BytecodeVerificationLocal &&
> loader_data->is_the_null_class_loader_data() &&
> !JvmtiExport::should_post_class_prepare())
>
> That way, there's no need to change systemDictionary.cpp.
>
>
I was going to take the suggestion, but realized that it would add
unnecessary complications for archived boot classes with class
pre-initialization support. Some agents may set
JvmtiExport::should_post_class_prepare(). It's worthwhile to support
class pre-init uniformly for archived boot classes with
JvmtiExport::should_post_class_prepare() enabled or disabled.
>
> BTW, I was wondering where the performance came from, so I wrote an
> investigative patch:
>
> diff -r 0702191777c9 src/hotspot/share/oops/instanceKlass.cpp
> --- a/src/hotspot/share/oops/instanceKlass.cpp Thu May 21 15:56:27
> 2020 -0700
> +++ b/src/hotspot/share/oops/instanceKlass.cpp Wed May 27 10:48:57
> 2020 -0700
> @@ -866,6 +866,13 @@
> return true;
> }
>
> + if (UseSharedSpaces && !BytecodeVerificationLocal &&
> is_shared_boot_class()) {
> + Handle h_init_lock(THREAD, init_lock());
> + ObjectLocker ol(h_init_lock, THREAD, h_init_lock() != NULL);
> + set_init_state(linked);
> + return true;
> + }
> +
> // trace only the link time for this klass that includes
> // the verification time
> PerfClassTraceTime vmtimer(ClassLoader::perf_class_link_time(),
>
>
> Benchmarking results (smaller numbers are better):
>
> (baseline vs your patch)
>
> baseline jiangli baseline jiangli
> 1: 58514375 57755638 (-758737) ----- 40.266 40.135 (
> -0.131) -
> 2: 58506426 57754623 (-751803) ----- 40.367 39.417 (
> -0.950) -----
> 3: 58498554 57759735 (-738819) ----- 40.513 39.970 (
> -0.543) ---
> 4: 58491265 57751296 (-739969) ----- 40.439 40.268 (
> -0.171) -
> 5: 58500588 57750975 (-749613) ----- 40.569 40.080 (
> -0.489) --
> 6: 58497015 57744418 (-752597) ----- 41.097 40.147 (
> -0.950) -----
> 7: 58494335 57749909 (-744426) ----- 39.983 40.214
> ( 0.231) +
> 8: 58500401 57750305 (-750096) ----- 40.235 40.417
> ( 0.182) +
> 9: 58490728 57767463 (-723265) ----- 40.354 39.928 (
> -0.426) --
> 10: 58497858 57746557 (-751301) ----- 40.756 39.706 (
> -1.050) -----
> ============================================================
> 58499154 57753091 (-746062) ----- 40.457 40.027 (
> -0.430) --
> instr delta = -746062 -1.2753%
> time delta = -0.430 ms -1.0619%
>
>
> (baseline vs my patch)
>
> baseline ioi baseline ioi
> 1: 58503574 57821124 (-682450) ----- 40.554 39.783 (
> -0.771) -----
> 2: 58499325 57819459 (-679866) ----- 40.092 40.325
> ( 0.233) ++
> 3: 58492362 57811978 (-680384) ----- 40.546 39.826 (
> -0.720) -----
> 4: 58488655 57828878 (-659777) ----- 40.270 40.550
> ( 0.280) ++
> 5: 58501567 57830179 (-671388) ----- 40.382 40.145 (
> -0.237) --
> 6: 58496552 57808774 (-687778) ----- 40.702 40.527 (
> -0.175) -
> 7: 58482701 57808925 (-673776) ----- 40.268 39.849 (
> -0.419) ---
> 8: 58493831 57807810 (-686021) ----- 40.396 39.940 (
> -0.456) ---
> 9: 58489388 57811354 (-678034) ----- 40.575 40.078 (
> -0.497) ---
> 10: 58482512 57795489 (-687023) ----- 40.084 40.247
> ( 0.163) +
> ============================================================
> 58493046 57814396 (-678650) ----- 40.386 40.126 (
> -0.260) --
> instr delta = -678650 -1.1602%
> time delta = -0.260 ms -0.6445%
>
>
> (your patch vs my patch)
>
> jiangli ioi jiangli ioi
> 1: 57716711 57782622 ( 65911) ++++ 41.042 40.302 (
> -0.740) -----
> 2: 57709666 57780196 ( 70530) ++++ 40.334 40.965 (
> 0.631) ++++
> 3: 57716074 57803315 ( 87241) +++++ 40.239 39.823 (
> -0.416) ---
> 4: 57725152 57782719 ( 57567) +++ 40.430 39.805 (
> -0.625) ----
> 5: 57719799 57787187 ( 67388) ++++ 40.138 40.003 (
> -0.135) -
> 6: 57721922 57769193 ( 47271) +++ 40.324 40.207 (
> -0.117) -
> 7: 57716438 57785212 ( 68774) ++++ 39.978 40.149 (
> 0.171) +
> 8: 57713834 57778797 ( 64963) ++++ 40.359 40.210 (
> -0.149) -
> 9: 57711272 57786376 ( 75104) ++++ 40.575 40.724 (
> 0.149) +
> 10: 57711660 57780548 ( 68888) ++++ 40.291 40.091 (
> -0.200) -
> ============================================================
> 57716252 57783615 ( 67363) ++++ 40.370 40.226 (
> -0.144) -
> instr delta = 67363 0.1167%
> time delta = -0.144 ms -0.3560%
>
>
> These numbers show that the majority of the time spent (678650
> instructions) inside InstanceKlass::link_class_impl is spent from the
> PerfClassTraceTime. Walking of the class hierarchy and taking the
> h_init_lock only takes about 67363 instructions).
>
> Due to this finding, I filed two more RFEs:
>
> https://bugs.openjdk.java.net/browse/JDK-8246019
> PerfClassTraceTime slows down VM start-up
>
It's related to JDK-8246020, and I've commented on the bug (see
JDK-8246020 comments). UsePerfData for perf data collection is common
in cloud usages. It's better to keep UsePerfData enabled by default.
>
> https://bugs.openjdk.java.net/browse/JDK-8246015
> Method::link_method is called twice for CDS methods
That was addressed as part of the initial change for JDK-8232222:
http://cr.openjdk.java.net/~jiangli/8232222/weberv.02/src/hotspot/share/oops/instanceKlass.cpp.frames.html
It's cleaner to handle it separately, so I removed it from the latest
version. I've assigned JDK-8246015 to myself and will address it
separately. Thanks for recording the separate bug.
Thanks!
Jiangli
>
>
> Thanks
> - Ioi
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