RFR (XXS): 8149442 : MonitorInUseLists should be on by default, deflate idle monitors taking too long

[Marcus Larsson]

Hi,


On 2016-04-01 10:48, David Simms wrote:
>
> Greetings,
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8149442
> Webrev: http://cr.openjdk.java.net/~dsimms/8149442/

Looks good to me!

Thanks,
Marcus

>
> Safe-point's "deflate_idle_monitors" (clean up task during 
> Safepoint::begin()), constantly scans all monitors, the entire 
> population. Setting MonitorInUseLists to true by default would seem 
> prudent, as the it reduces the scan to "InUse" thread lists. Reduction 
> in "deflate idle monitor" execution time of up to a magnitude.
>
>    There are certain applications (notably SPECjbb2013 use of ForkJoin)
>    whose Java lock monitor total populations are quite high, but the
>    actual number of in use monitors is low.
>
>    Why these total populations grow so large, further work to reduce
>    "deflate idle monitor" operations, is beyond the scope of this bug
>    (see JDK-7021979 & JDK-8153224).
>
> Testing: no regressions spotted on the following benchmarks:
>
>  * SpecJbb2005
>  * SpecJbb2008
>  * SpecJbb2013
>  * Volano
>
>
>
> Cheers
> / David Simms