RFR(S) Contended Locking fast exit bucket (8073165)

Daniel D. Daugherty daniel.daugherty at oracle.com
Fri Mar 13 15:39:00 UTC 2015


Thanks for chiming in on the thread and for the links...

I'll likely roll my reply to this e-mail up with my reply to
David H early next week...


On 3/13/15 8:05 AM, Aleksey Shipilev wrote:
> On 03/13/2015 07:50 AM, David Holmes wrote:
>>> - remove old mfence() support
>> So I had expected to see this change conditional on the runtime
>> processor type. But then I checked Dave's blog and saw this was
>> determined 5+ years ago (!!!) so those older processors are no longer a
>> consideration. I do hope the performance tests have been re-run since
>> then though ;-)
> MFENCE still has stronger ordering guarantees, and LOCK'ed instructions
> are faster for regular accesses. Note that we also observed the
> performance effects when doing blind "lock addl %(rsp), 0":
>    https://bugs.openjdk.java.net/browse/JDK-8050147
>    http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/51e474c55d20
>    http://shipilev.net/blog/2014/on-the-fence-with-dependencies/
> Thanks,
> -Aleksey.

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