Hi Serguei,
First off, thanks as always for looking at this :-) Let
me inline my answers:
I actually "struggled" with this part of the change. My
change is correct semantically and if you care about
performance for when sampling a given thread.
Your change will work semantically but the performance
is the same as the global sampling.
What I mean by working semantically is that that the
tests and the code will work. However, this means that
all threads will be doing the sampling work but when
the code will post the event here:
->
http://cr.openjdk.java.net/~jcbeyler/8201655/webrev.02/src/hotspot/share/prims/jvmtiExport.cpp.udiff.html
<http://cr.openjdk.java.net/%7Ejcbeyler/8201655/webrev.02/src/hotspot/share/prims/jvmtiExport.cpp.udiff.html>
(which is why your suggestion works, the change in
jvmtiExport basically ensures only the threads
requested are posting events)
The code will check that we actually only post for
threads we care about. The code above ensures that only
threads that were requested to be sampling are the ones
that are sampling internally.
Note: I REALLY prefer your suggestion for two reasons:
- We do not change the runtime/GC code at all, it
remains "simple"
- The overhead in the general case goes away and this
is a NOP for my actual use-case from a performance
point of view (sampling every thread)
But:
- Then sampling per thread really is just telling the
system don't pollute the callbacks, though internally
you are doing all the work anyway.
Let me know which you prefer :)
Also, do you see that enabling the sampling events globally
still works?
Yes, otherwise HeapMonitorThreadTest.java would fail
since it checks that.
http://cr.openjdk.java.net/%7Ejcbeyler/8201655/webrev.02/test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/libHeapMonitorTest.c.frames.html
A couple of places where err is declared as int instead of
jvmtiError:
714 int err;
742 int err; Should not be silent in a case of
JVMTI error: 744 err = (*jvmti)->GetThreadInfo(jvmti, thread,
&info);
745 if (err != JVMTI_ERROR_NONE) {
746 return;
Done and done, I added a fprintf on stderr saying the
GetThreadInfo failed and the test is ignoring the add
count.
Thanks again for looking and let me know what you think,
Jc
On Mon, Nov 5, 2018 at 2:25 PM
serguei.spit...@oracle.com
<mailto:serguei.spit...@oracle.com>
<serguei.spit...@oracle.com
<mailto:serguei.spit...@oracle.com>> wrote:
Hi Jc,
It looks good in general but I have some comments
below.
http://cr.openjdk.java.net/%7Ejcbeyler/8201655/webrev.02/src/hotspot/share/gc/shared/memAllocator.cpp.udiff.html
+static bool thread_enabled_for_one_jvmti_env() {
+ JavaThread *thread = JavaThread::current();
+ JvmtiThreadState *state =
thread->jvmti_thread_state();
+ if (state == NULL) {
+ return false;
+ }
+
+ JvmtiEnvThreadStateIterator it(state);
+ for (JvmtiEnvThreadState* ets = it.first(); ets
!= NULL; ets = it.next(ets)) {
+ if
(ets->is_enabled(JVMTI_EVENT_SAMPLED_OBJECT_ALLOC)) {
+ return true;
+ }
+ }
+
+ return false;
+}
+
void
MemAllocator::Allocation::notify_allocation_jvmti_sampler() {
// support for JVMTI VMObjectAlloc event (no-op if not
enabled)
JvmtiExport::vm_object_alloc_event_collector(obj());
if (!JvmtiExport::should_post_sampled_object_alloc()) {
// Sampling disabled
return;
}
+ // Sampling is enabled for at least one thread,
is it this one?
+ if (!thread_enabled_for_one_jvmti_env()) {
+ return;
+ }
+ I don't think you need this change as this
condition already does it: if
(!JvmtiExport::should_post_sampled_object_alloc()) {
// Sampling disabled
return;
}
Please, look at the following line in the
jvmtiEventController.cpp:
JvmtiExport::set_should_post_sampled_object_alloc((any_env_thread_enabled &
SAMPLED_OBJECT_ALLOC_BIT) != 0);
I hope, testing will prove my suggestion is correct.
Also, do you see that enabling the sampling events globally
still works?
http://cr.openjdk.java.net/%7Ejcbeyler/8201655/webrev.02/test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/libHeapMonitorTest.c.frames.html
A couple of places where err is declared as int instead of
jvmtiError:
714 int err;
742 int err; Should not be silent in a case of
JVMTI error: 744 err = (*jvmti)->GetThreadInfo(jvmti, thread,
&info);
745 if (err != JVMTI_ERROR_NONE) {
746 return;
Thanks,
Serguei
On 10/26/18 10:48, JC Beyler wrote:
Hi all,
When working on the heap sampling, I had promised
to do the per thread event so here it is!
Could I get a review for this:
Webrev:
http://cr.openjdk.java.net/~jcbeyler/8201655/webrev.02/
<http://cr.openjdk.java.net/%7Ejcbeyler/8201655/webrev.02/>
Bug: https://bugs.openjdk.java.net/browse/JDK-8201655
I was thinking of adding GC-dev for the
memAllocator change once I get favorable reviews
for the rest of the change.
I've done a bit of performance testing and on the
Dacapo benchmark I see no change in performance
when turned off (logical, any code change is
behind a flag check already in place) and when
turned on it is comparable to the current performance.
(More information is: I see a very slight
degradation if we are doing 512k sampling but no
degradation at 2MB).
Thanks,
Jc
--
Thanks,
Jc
