Hi Martin,
thanks a lot for reviewing and the feedback. I'll dig into the details as soon
as possible. Looking forward to it :)
Thanks, Richard.
-----Original Message-----
From: Doerr, Martin <martin.do...@sap.com>
Sent: Donnerstag, 12. März 2020 17:28
To: Reingruber, Richard <richard.reingru...@sap.com>; 'Robbin Ehn'
<robbin....@oracle.com>; Lindenmaier, Goetz <goetz.lindenma...@sap.com>; David
Holmes <david.hol...@oracle.com>; Vladimir Kozlov (vladimir.koz...@oracle.com)
<vladimir.koz...@oracle.com>; serviceability-dev@openjdk.java.net;
hotspot-compiler-...@openjdk.java.net; hotspot-runtime-...@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/IterateHeapWithEscapeAnalysisEnabled.java
test/hotspot/jtreg/serviceability/jvmti/Heap/libIterateHeapWithEscapeAnalysisEnabled.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-
> boun...@openjdk.java.net> On Behalf Of Reingruber, Richard
> Sent: Dienstag, 3. März 2020 21:23
> To: 'Robbin Ehn' <robbin....@oracle.com>; Lindenmaier, Goetz
> <goetz.lindenma...@sap.com>; David Holmes <david.hol...@oracle.com>;
> Vladimir Kozlov (vladimir.koz...@oracle.com)
> <vladimir.koz...@oracle.com>; serviceability-dev@openjdk.java.net;
> hotspot-compiler-...@openjdk.java.net; hotspot-runtime-
> d...@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....@oracle.com>
> Sent: Monday, March 2, 2020 11:17 AM
> To: Lindenmaier, Goetz <goetz.lindenma...@sap.com>; Reingruber, Richard
> <richard.reingru...@sap.com>; David Holmes <david.hol...@oracle.com>;
> Vladimir Kozlov (vladimir.koz...@oracle.com)
> <vladimir.koz...@oracle.com>; serviceability-dev@openjdk.java.net;
> hotspot-compiler-...@openjdk.java.net; hotspot-runtime-
> d...@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.hol...@oracle.com>
> >> Sent: Donnerstag, 19. Dezember 2019 03:12
> >> To: Reingruber, Richard <richard.reingru...@sap.com>; serviceability-
> >> d...@openjdk.java.net; hotspot-compiler-...@openjdk.java.net;
> hotspot-
> >> runtime-...@openjdk.java.net; Vladimir Kozlov
> (vladimir.koz...@oracle.com)
> >> <vladimir.koz...@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.hol...@oracle.com>
> >>> Sent: Dienstag, 17. Dezember 2019 08:03
> >>> To: Reingruber, Richard <richard.reingru...@sap.com>; serviceability-
> >> d...@openjdk.java.net; hotspot-compiler-...@openjdk.java.net;
> hotspot-
> >> runtime-...@openjdk.java.net; Vladimir Kozlov
> (vladimir.koz...@oracle.com)
> >> <vladimir.koz...@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.hol...@oracle.com>
> >>>>> Sent: Freitag, 13. Dezember 2019 00:56
> >>>>> To: Reingruber, Richard <richard.reingru...@sap.com>;
> >>>>> serviceability-dev@openjdk.java.net;
> >>>>> hotspot-compiler-...@openjdk.java.net;
> >>>>> hotspot-runtime-...@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.hol...@oracle.com>
> >>>>>>> Sent: Mittwoch, 11. Dezember 2019 08:03
> >>>>>>> To: Reingruber, Richard <richard.reingru...@sap.com>;
> >>>>>>> serviceability-dev@openjdk.java.net;
> >>>>>>> hotspot-compiler-...@openjdk.java.net;
> >>>>>>> hotspot-runtime-...@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
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
