Good summary with a list of solutions below!
On 11/27/18 2:50 PM, dean.l...@oracle.com wrote:
Let me list the proposed solutions:
1. short-circuit compiles in CompilationPolicy::event in
is_interp_only_mode
2. detect is_interp_only_mode in resolve stubs and force a c2i call
3. don't offer a JVMTI suspend point in resolve stubs (or
JavaCallWrapper)
Solution 1 penalizes other threads, and don't prevent other threads
from compiling the method, so while it may help a little, it's incomplete.
I doubt, the Solution 1 penalizes other threads.
First, it is an important pretty frequent/common case that allows to
save on compilations.
Second, there is no point to compile methods on a thread executed in
interp_only_mode.
Also, there is no big advantage to compile methods even for other threads
when an active debugging (e.g. single stepping) is in progress.
Third, this would make it consistent with what the the interpreter is doing.
So, I think, the Solution 1 is needed independently of other solutions
we take.
My suggestion is to apply it in the JDK-8195639 bug fix.
Solutions 1 and 2 allow the thread to resume in a different method
(the callee method), causing other problems.
Agreed.
With Solution 3, the frame we suspend is the same as the frame we end
up in after the resume, so I believe it solves all the problems.
IMHO this is the correct solution to pursue.
I agree in general.
This solution has some risks involved as it impacts a lot of code
including platform-independent.
It is also going to fix the other bugs: JDK-8195635, JDK-8214093,
JDK-8207013 (not sure about all of them yet).
My suggestion is to pursue it as the JDK-8195635 fix.
Could you, please, confirm if works for you?
Also, we have no consensus yet on the Solution 1.
Thanks,
Serguei
dl
On 11/27/18 2:19 PM, serguei.spit...@oracle.com wrote:
Hi Dean,
You also asked the questions:
> Doesn't is_interp_only_mode() only apply to the current thread?
Yes it does.
> I don't think it's safe to assume no compiles will happen in other
threads,
> or that a method call target is not already compiled, because as far
> as I can tell, JVMTI only deoptimizes the active frames.
I agree with it.
However, compilations on the thread with the interp_only_mode enabled
is the most important case.
Disabling compilations such thread improves testing stability.
> The bug report describes a case where the caller has been deoptimized
> while resolving a call. I don't see how this fix prevents the target
> from being a previously compiled method.
> But we do need to make sure not to call into compiled code, so I think
> the fix needs to be in code like
SharedRuntime::resolve_static_call_C(),
> where it returns get_c2i_entry() if is_interp_only_mode() is true.
Thank you for making this point.
It would be nice to attack this as well.
We can try to investigate this approach further.
One problem is that there are more cases like resolve_static_call_C,
for instance, resolve_virtual_call_C and resolve_opt_virtual_call_C.
We may need to fix the same in other places, like
JavaCallWrapper::JavaCallWrapper.
We can start from fixing it in the resolve_static_call_C.
If it is successful then continue this effort for other cases as well.
What do you think?
Thanks,
Serguei
On 11/27/18 1:01 PM, Alex Menkov wrote:
Hi Dean,
Thank you for the feedback and for the comments in Jira.
>> How does this solve the problem of
>> HotSpotJVMCIRuntime.adjustCompilationLevel being called?
It doesn't. It fixes another issue.
The test suspend test thread and ensures that top frame is a
"fibonachi" method. Then it turns SingleStep on, does PopFrame and
resumes the thread.
The problem is the thread continues execution of compiled code
(ignoring SingleStep) and we get SindleStep event only when
adjustCompilationLevel method is called (it's interpreted code).
There are several other bugs which are (most likely) caused by
suspend during call setup (JDK-8195635, JDK-8214093, JDK-8207013)
--alex
On 11/27/2018 01:39, serguei.spit...@oracle.com wrote:
Hi Dean,
Thank you a lot for looking at this!
Just a couple of points from me (it is up to Alex to provide a full
answer).
I think, Alex in this RFR missed to tell that we knew about this
issue that an incorrect frame will be popped.
But after some discussion we decided to file a separate issue on this.
Alex wanted to create a good stand-alone test case demonstrating
this problem before filing it.
Now, as I can see, the JDK-8195635
<https://bugs.openjdk.java.net/browse/JDK-8195635> looks very close
to a bug that we wanted to file.
The only difference is that our scenario includes the
SharedRuntime::resolve_static_call_C instead of the
JavaCallWrapper::JavaCallWrapper as a helper for Java method
invocation.
If I understand corrctly (Alex will fix me if needed), the jtreg
test we used to chase this issue did not catch a problem with the
HotSpotJVMCIRuntime.adjustCompilationLevel.
The suggested fix was to fix the mismatch in the
TieredThresholdPolicy::even with the comment in the interpreter code:
nmethod* InterpreterRuntime::frequency_counter_overflow(JavaThread*
thread, address branch_bcp) {
. . .
if (nm != NULL && thread->is_interp_only_mode()) {
// Normally we never get an nm if is_interp_only_mode() is
true, because
// policy()->event has a check for this and won't compile the
method when
// true. However, it's possible for is_interp_only_mode() to
become true
// during the compilation. We don't want to return the nm in
that case
// because we want to continue to execute interpreted.
nm = NULL;
}
> So I think the fix needs to be in code like
SharedRuntime::resolve_static_call_C(),
> where it returns get_c2i_entry() if is_interp_only_mode() is true.
I'm not sure, the adding this condition and returning the
get_c2i_entry() is always correct.
We need some help from the Compiler team to make it right.
BTW, the interp_only_mode has been enabled only when some
interp_only events are enabled.
It is not set by either PopFrame or ForceEarlyReturn.
But the popframe009 test enables single stepping, so we wanted to
make this part right.
Thanks,
Serguei
On 11/26/18 16:05, dean.l...@oracle.com wrote:
How does this solve the problem of
HotSpotJVMCIRuntime.adjustCompilationLevel being called?
I don't think this fix is the right approach. Doesn't
is_interp_only_mode() only apply to the current thread? I don't
think it's safe to assume no compiles will happen in other
threads, or that a method call target is not already compiled,
because as far as I can tell, JVMTI only deoptimizes the active
frames. The bug report describes a case where the caller has been
deoptimized while resolving a call. I don't see how this fix
prevents the target from being a previously compiled method. But
we do need to make sure not to call into compiled code, so I think
the fix needs to be in code like
SharedRuntime::resolve_static_call_C(), where it returns
get_c2i_entry() if is_interp_only_mode() is true. However, there
is still another problem. By allowing JVMTI to suspend the thread
during call setup, but reporting the frame as still in the caller
instead of the callee, we confuse JVMTI into thinking that
execution will resume in the caller instead of the callee. We may
want to restrict where we offer JVMTI suspend points, and not
offer a JVMTI suspend point in
SharedRuntime::resolve_static_call_C and friends at all.
dl
On 11/26/18 11:14 AM, Alex Menkov wrote:
Hi all,
Please review the fix for
https://bugs.openjdk.java.net/browse/JDK-8195639
webrev:
http://cr.openjdk.java.net/~amenkov/popframe009/webrev.01/
Description:
The test suspends a thread, turns on single stepping and then
calls PopFrame. SingleStep event is expected as soon as the
thread is resumed and PopFrame is processed (so we have call
stack with the depth 1 less than it was before PopFrame). Instead
SingleStep event is received with much deeper call stack (and
PopFrame processes wrong frame).
Research shown that this is caused by missed deoptimization of
the current frame.
As far as I understand CompilationPolicy::event should handle the
case when the thread has is_interp_only_mode() set, but
TieredThresholdPolicy::event checks this only then CompLevel is
CompLevel_none.
CompilerRuntime always calls policy()->event with CompLevel ==
CompLevel_aot.
The fix looks quite simple, but I'd appreciate feedback from
runtime and compiler teams as I'm not sure I completely
understand all the details of the "PopFrame dance".
--alex
