RFR: 8330969: scalability issue with loaded JVMTI agent

[Serguei Spitsyn]

On Thu, 25 Apr 2024 20:39:03 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

>> This is a fix of the following JVMTI scalability issue. A closed benchmark with millions of virtual threads shows 3X-4X overhead when a JVMTI agent has been loaded. For instance, this is observable when an app is executed under control of the Oracle Studio `collect` utility.
>> For performance analysis, experiments and numbers, please, see the comment below this description.
>> 
>> The fix is to replace the global counter `_VTMS_transition_count` with the mark bit `_VTMS_transition_mark` in each `JavaThread`'.
>> 
>> Testing:
>>  - Tested with mach5 tiers 1-6
>
> src/hotspot/share/prims/jvmtiEnvBase.cpp line 1638:
> 
>> 1636:   // Iterates over all JavaThread's, counts VTMS transitions and restores
>> 1637:   // jt->jvmti_thread_state() and jt->jvmti_vthread() for VTMS transition protocol.
>> 1638:   void count_transitions_and_correct_jvmti_thread_states() {
> 
> The method doesn't count anything anymore.
> Rename it to `correct_jvmti_thread_states()`?
> Comment needs to be updated too.

Good suggestion, thanks. Renamed function and corrected the comment.

> src/hotspot/share/prims/jvmtiThreadState.cpp line 501:
> 
>> 499:   oop vt = JNIHandles::resolve_external_guard(vthread);
>> 500:   java_lang_Thread::set_is_in_VTMS_transition(vt, false);
>> 501:   assert(thread->VTMS_transition_mark(), "sanity ed_heck");
> 
> Suggestion:
> 
>   assert(thread->VTMS_transition_mark(), "sanity check");

Thanks. Fixed now.

> src/hotspot/share/runtime/javaThread.hpp line 668:
> 
>> 666:   void toggle_is_disable_suspend()               { _is_disable_suspend = !_is_disable_suspend; };
>> 667: 
>> 668:   bool VTMS_transition_mark()                    { return Atomic::load(&_VTMS_transition_mark); }
> 
> Suggestion:
> 
>   bool VTMS_transition_mark() const              { return Atomic::load(&_VTMS_transition_mark); }

Good suggestion, thanks. Fixed now.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/18937#discussion_r1580607373
PR Review Comment: https://git.openjdk.org/jdk/pull/18937#discussion_r1580610256
PR Review Comment: https://git.openjdk.org/jdk/pull/18937#discussion_r1580612160