Very long safepoint pauses for RevokeBias

[David Holmes]

On 19/05/2015 2:24 AM, Christopher Berner wrote:
> Don't think it got truncated, but I only included the first line of log
> about the safepoint statistics. Turning off biased locks seem to have
> fixed those pauses, thanks!
>
> Just to help me understand, what circumstances would cause biased
> locking to induce 28sec pauses? Is that because a thread was holding the
> lock for 28sec?

No. Based on the stats you showed the actual revocation is only a 
fraction of the time spent. It is taking a long time to get the system 
to a safepoint and then a reasonable amount of time is also being spent 
on safepoint cleanup tasks.

Do you have hundreds of active threads?

David
-----

> On Sun, May 17, 2015 at 1:54 PM, David Holmes <david.holmes at oracle.com
> <mailto:david.holmes at oracle.com>> wrote:
>
>     Hi Christopher,
>
>
>     On 16/05/2015 10:38 AM, Christopher Berner wrote:
>
>         I work on the Presto project, which is a distributed SQL engine, and
>         intermittently (roughly once an hour) I see very long
>         application stopped
>         times (as reported by
>              -XX:+PrintGCApplicationStoppedTime). I enabled safepoint
>         statistics, and
>         see that the pause seems to be coming from a RevokeBias safepoint.
>
>         Any suggestions as to how I can debug this? I already tried adding
>         -XX:+PerfDisableSharedMem, in case this was related to
>         https://bugs.openjdk.java.net/browse/JDK-8076103
>
>         See below for safepoint statistics:
>
>                    vmop                    [threads: total initially_running
>         wait_to_block]    [time: spin block sync cleanup vmop]
>         page_trap_count
>
>         2528.893: RevokeBias                       [     872          0
>             6    ]      [     0 12826 13142  6476  8177    ]  0
>
>
>     Your email seems to be truncated?
>
>     But just to be sure, does the application run okay with
>     biased-locking disabled?
>
>     David
>
>