Very long safepoint pauses for RevokeBias

[Vitaly Davidovich]

Slight tangent - is biased locking even a worthwhile feature on modern CPUs
where non-contended (or even better, cache hitting) CAS is fairly cheap?

sent from my phone
On May 19, 2015 4:02 AM, "David Holmes" <david.holmes at oracle.com> wrote:

> 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
>>
>>
>>