RFR(M): 8151085: Change G1 concurrent timer and tracer measuring time
sangheon
sangheon.kim at oracle.com
Fri Mar 11 19:48:26 UTC 2016
Hi all,
Could I have some reviews for this change?
Concurrent gc timer and tracer are mainly used from concurrent mark
thread except when abort happens. This abort results in a race condition
between VM thread and concurrent mark thread.
So I propose to do timer and tracer related works only from concurrent
mark thread.
Measurements are changed like below:
Current
Proposal
Start timer and tracer
When Young Initial Mark GC starts from VM thread
When actually starts concurrent cycle from concurrent mark thread
End timer and tracer
1. At the end of concurrent cycle
2. When abort happens At the end of concurrent cycle
* I think this will be okay as even though we abort, we continue working
for concurrent stuffs to finish concurrent work cycle. And we were just
not measuring them.
Heap summary (before-gc)
At the beginning of Young Initial Mark GC.
But concurrent mark thread is not working at that time. At the start of
concurrent cycle.
Heap summary (after-gc)
1. When abort happens before cleanup: sent when abort happens.
2. When abort happens after cleanup or normal case(w/o abort): sent at
the end of cleanup. At the end of concurrent cycle which means it will
include all minor clearing after 'Pause Cleanup'.
This proposal also includes related changes like below:
1. Removed the patch for JDK-8149834(race between VM thread and
concurrent mark thread for concurrent gc timer): 8149834 was making
related functions atomically while this proposal is changing not to
happen that race.
2. Removed G1CollectorState::_concurrent_cycle_started: no longer needed
as related logics are running from concurrent mark thread.
Currently 'total concurrent time' is not same as 'sum of concurrent
phases' and the reason is that the concurrent timer is started when
young initial mark gc happens. Secondly, concurrent mark thread is not
counting the time for waiting VMThread to finish VM
operation(SuspendibleThreadSet).
I am planning to enhance this after '8151614: Improve logging in
concurrent mark code' is pushed.
CR: https://bugs.openjdk.java.net/browse/JDK-8151085
Webrev: http://cr.openjdk.java.net/~sangheki/8151085/webrev.00
Testing: JPRT, RBT(hotspot_all, testlist: running now), local reproducer
for JDK-8149834
Thanks,
Sangheon
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/hotspot-gc-dev/attachments/20160311/7cb17e06/attachment.htm>
More information about the hotspot-gc-dev
mailing list