Hi Patricio, Vladimir, and Serguei,
now that direct handshakes are available, I've updated the patch to make use of
them.
In addition I have done some clean-up changes I missed in the first webrev.
Finally I have implemented the workaround suggested by Patricio to avoid
nesting the handshake
into the vm operation VM_SetFramePop [1]
Kindly review again:
Webrev: http://cr.openjdk.java.net/~rrich/webrevs/8238585/webrev.1/
Webrev(delta): http://cr.openjdk.java.net/~rrich/webrevs/8238585/webrev.1.inc/
I updated the JBS item explaining why the vm operation VM_EnterInterpOnlyMode
can be replaced with a
direct handshake:
JBS: https://bugs.openjdk.java.net/browse/JDK-8238585
Testing:
* JCK and JTREG tests, also in Xcomp mode with fastdebug and release builds on
all platforms.
* Submit-repo: mach5-one-rrich-JDK-8238585-20200423-1436-10441737
Thanks,
Richard.
[1] An assertion in Handshake::execute_direct() fails, if called be VMThread,
because it is no JavaThread.
-----Original Message-----
From: hotspot-dev <hotspot-dev-boun...@openjdk.java.net> On Behalf Of
Reingruber, Richard
Sent: Freitag, 14. Februar 2020 19:47
To: Patricio Chilano <patricio.chilano.ma...@oracle.com>;
serviceability-dev@openjdk.java.net; hotspot-compiler-...@openjdk.java.net;
hotspot-...@openjdk.java.net; hotspot-runtime-...@openjdk.java.net;
hotspot-gc-...@openjdk.java.net
Subject: RE: RFR(S) 8238585: Use handshake for
JvmtiEventControllerPrivate::enter_interp_only_mode() and don't make compiled
methods on stack not_entrant
Hi Patricio,
> > I'm really glad you noticed the problematic nesting. This seems to be a
general issue: currently a
> > handshake cannot be nested in a vm operation. Maybe it should be
asserted in the
> > Handshake::execute() methods that they are not called by the vm thread
evaluating a vm operation?
> >
> > > Alternatively I think you could do something similar to what we do
in
> > > Deoptimization::deoptimize_all_marked():
> > >
> > > EnterInterpOnlyModeClosure hs;
> > > if (SafepointSynchronize::is_at_safepoint()) {
> > > hs.do_thread(state->get_thread());
> > > } else {
> > > Handshake::execute(&hs, state->get_thread());
> > > }
> > > (you could pass “EnterInterpOnlyModeClosure” directly to the
> > > HandshakeClosure() constructor)
> >
> > Maybe this could be used also in the Handshake::execute() methods as
general solution?
> Right, we could also do that. Avoiding to clear the polling page in
> HandshakeState::clear_handshake() should be enough to fix this issue and
> execute a handshake inside a safepoint, but adding that "if" statement
> in Hanshake::execute() sounds good to avoid all the extra code that we
> go through when executing a handshake. I filed 8239084 to make that
change.
Thanks for taking care of this and creating the RFE.
>
> > > I don’t know JVMTI code so I’m not sure if VM_EnterInterpOnlyMode
is
> > > always called in a nested operation or just sometimes.
> >
> > At least one execution path without vm operation exists:
> >
> > JvmtiEventControllerPrivate::enter_interp_only_mode(JvmtiThreadState
*) : void
> >
JvmtiEventControllerPrivate::recompute_thread_enabled(JvmtiThreadState *) : jlong
> > JvmtiEventControllerPrivate::recompute_enabled() : void
> > JvmtiEventControllerPrivate::change_field_watch(jvmtiEvent,
bool) : void (2 matches)
> > JvmtiEventController::change_field_watch(jvmtiEvent, bool) :
void
> > JvmtiEnv::SetFieldAccessWatch(fieldDescriptor *) :
jvmtiError
> > jvmti_SetFieldAccessWatch(jvmtiEnv *, jclass, jfieldID)
: jvmtiError
> >
> > I tend to revert back to VM_EnterInterpOnlyMode as it wasn't my main
intent to replace it with a
> > handshake, but to avoid making the compiled methods on stack
not_entrant.... unless I'm further
> > encouraged to do it with a handshake :)
> Ah! I think you can still do it with a handshake with the
> Deoptimization::deoptimize_all_marked() like solution. I can change the
> if-else statement with just the Handshake::execute() call in 8239084.
> But up to you. : )
Well, I think that's enough encouragement :)
I'll wait for 8239084 and try then again.
(no urgency and all)
Thanks,
Richard.
-----Original Message-----
From: Patricio Chilano <patricio.chilano.ma...@oracle.com>
Sent: Freitag, 14. Februar 2020 15:54
To: Reingruber, Richard <richard.reingru...@sap.com>;
serviceability-dev@openjdk.java.net; hotspot-compiler-...@openjdk.java.net;
hotspot-...@openjdk.java.net; hotspot-runtime-...@openjdk.java.net;
hotspot-gc-...@openjdk.java.net
Subject: Re: RFR(S) 8238585: Use handshake for
JvmtiEventControllerPrivate::enter_interp_only_mode() and don't make compiled
methods on stack not_entrant
Hi Richard,
On 2/14/20 9:58 AM, Reingruber, Richard wrote:
Hi Patricio,
thanks for having a look.
> I’m only commenting on the handshake changes.
> I see that operation VM_EnterInterpOnlyMode can be called inside
> operation VM_SetFramePop which also allows nested operations. Here is a
> comment in VM_SetFramePop definition:
>
> // Nested operation must be allowed for the VM_EnterInterpOnlyMode that
is
> // called from the JvmtiEventControllerPrivate::recompute_thread_enabled.
>
> So if we change VM_EnterInterpOnlyMode to be a handshake, then now we
> could have a handshake inside a safepoint operation. The issue I see
> there is that at the end of the handshake the polling page of the target
> thread could be disarmed. So if the target thread happens to be in a
> blocked state just transiently and wakes up then it will not stop for
> the ongoing safepoint. Maybe I can file an RFE to assert that the
> polling page is armed at the beginning of disarm_safepoint().
I'm really glad you noticed the problematic nesting. This seems to be a general
issue: currently a
handshake cannot be nested in a vm operation. Maybe it should be asserted in the
Handshake::execute() methods that they are not called by the vm thread
evaluating a vm operation?
> Alternatively I think you could do something similar to what we do in
> Deoptimization::deoptimize_all_marked():
>
> EnterInterpOnlyModeClosure hs;
> if (SafepointSynchronize::is_at_safepoint()) {
> hs.do_thread(state->get_thread());
> } else {
> Handshake::execute(&hs, state->get_thread());
> }
> (you could pass “EnterInterpOnlyModeClosure” directly to the
> HandshakeClosure() constructor)
Maybe this could be used also in the Handshake::execute() methods as general
solution?
Right, we could also do that. Avoiding to clear the polling page in
HandshakeState::clear_handshake() should be enough to fix this issue and
execute a handshake inside a safepoint, but adding that "if" statement
in Hanshake::execute() sounds good to avoid all the extra code that we
go through when executing a handshake. I filed 8239084 to make that change.
> I don’t know JVMTI code so I’m not sure if VM_EnterInterpOnlyMode is
> always called in a nested operation or just sometimes.
At least one execution path without vm operation exists:
JvmtiEventControllerPrivate::enter_interp_only_mode(JvmtiThreadState *) :
void
JvmtiEventControllerPrivate::recompute_thread_enabled(JvmtiThreadState
*) : jlong
JvmtiEventControllerPrivate::recompute_enabled() : void
JvmtiEventControllerPrivate::change_field_watch(jvmtiEvent, bool) :
void (2 matches)
JvmtiEventController::change_field_watch(jvmtiEvent, bool) : void
JvmtiEnv::SetFieldAccessWatch(fieldDescriptor *) : jvmtiError
jvmti_SetFieldAccessWatch(jvmtiEnv *, jclass, jfieldID) :
jvmtiError
I tend to revert back to VM_EnterInterpOnlyMode as it wasn't my main intent to
replace it with a
handshake, but to avoid making the compiled methods on stack not_entrant....
unless I'm further
encouraged to do it with a handshake :)
Ah! I think you can still do it with a handshake with the
Deoptimization::deoptimize_all_marked() like solution. I can change the
if-else statement with just the Handshake::execute() call in 8239084.
But up to you. : )
Thanks,
Patricio
Thanks again,
Richard.
-----Original Message-----
From: Patricio Chilano <patricio.chilano.ma...@oracle.com>
Sent: Donnerstag, 13. Februar 2020 18:47
To: Reingruber, Richard <richard.reingru...@sap.com>;
serviceability-dev@openjdk.java.net; hotspot-compiler-...@openjdk.java.net;
hotspot-...@openjdk.java.net; hotspot-runtime-...@openjdk.java.net;
hotspot-gc-...@openjdk.java.net
Subject: Re: RFR(S) 8238585: Use handshake for
JvmtiEventControllerPrivate::enter_interp_only_mode() and don't make compiled
methods on stack not_entrant
Hi Richard,
I’m only commenting on the handshake changes.
I see that operation VM_EnterInterpOnlyMode can be called inside
operation VM_SetFramePop which also allows nested operations. Here is a
comment in VM_SetFramePop definition:
// Nested operation must be allowed for the VM_EnterInterpOnlyMode that is
// called from the JvmtiEventControllerPrivate::recompute_thread_enabled.
So if we change VM_EnterInterpOnlyMode to be a handshake, then now we
could have a handshake inside a safepoint operation. The issue I see
there is that at the end of the handshake the polling page of the target
thread could be disarmed. So if the target thread happens to be in a
blocked state just transiently and wakes up then it will not stop for
the ongoing safepoint. Maybe I can file an RFE to assert that the
polling page is armed at the beginning of disarm_safepoint().
I think one option could be to remove
SafepointMechanism::disarm_if_needed() in
HandshakeState::clear_handshake() and let each JavaThread disarm itself
for the handshake case.
Alternatively I think you could do something similar to what we do in
Deoptimization::deoptimize_all_marked():
EnterInterpOnlyModeClosure hs;
if (SafepointSynchronize::is_at_safepoint()) {
hs.do_thread(state->get_thread());
} else {
Handshake::execute(&hs, state->get_thread());
}
(you could pass “EnterInterpOnlyModeClosure” directly to the
HandshakeClosure() constructor)
I don’t know JVMTI code so I’m not sure if VM_EnterInterpOnlyMode is
always called in a nested operation or just sometimes.
Thanks,
Patricio
On 2/12/20 7:23 AM, Reingruber, Richard wrote:
// Repost including hotspot runtime and gc lists.
// Dean Long suggested to do so, because the enhancement replaces a vm operation
// with a handshake.
// Original thread:
http://mail.openjdk.java.net/pipermail/serviceability-dev/2020-February/030359.html
Hi,
could I please get reviews for this small enhancement in hotspot's jvmti
implementation:
Webrev: http://cr.openjdk.java.net/~rrich/webrevs/8238585/webrev.0/
Bug: https://bugs.openjdk.java.net/browse/JDK-8238585
The change avoids making all compiled methods on stack not_entrant when
switching a java thread to
interpreter only execution for jvmti purposes. It is sufficient to deoptimize
the compiled frames on stack.
Additionally a handshake is used instead of a vm operation to walk the stack
and do the deoptimizations.
Testing: JCK and JTREG tests, also in Xcomp mode with fastdebug and release
builds on all platforms.
Thanks, Richard.
See also my question if anyone knows a reason for making the compiled methods
not_entrant:
http://mail.openjdk.java.net/pipermail/serviceability-dev/2020-January/030339.html
