RFR: 8280139: Report more detailed statistics about task stealing in task queue stats [v2]
Thomas Schatzl
tschatzl at openjdk.java.net
Mon Jan 31 16:02:06 UTC 2022
On Thu, 20 Jan 2022 11:11:22 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:
>> Hi all,
>>
>> can I have reviews that improves task queue statistics?
>>
>> This is a step to see problems with task queue in general and measure future task stealing improvements in GC; particularly contention on steal information has shown to be correlated to performance, so information about basic occurrences during stealing (how many empty, how many contended, how many contended in a row, max contended accesses in a row) in the task queue is very interesting for further performance work.
>>
>> Old output of `gc+tasks+stats=trace` after compiling in these statistics:
>>
>> thr qpush qpop qpop-s qattempt qsteal opush omax
>> --- ---------- ---------- ---------- ---------- ---------- ---------- ----------
>> 0 3777115 3776816 3872 17434 9630 0 0
>>
>> And new:
>>
>> thr push pop pop-slow st-attempt st-empty st-ctdd st-success st-ctdd-max st-biasdrop ovflw-push ovflw-max
>> --- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- -----------
>> 0 4616264 4616218 3608 12945 1 1650 11294 5 9405 0 0
>> [...]
>>
>> The first four columns stayed the same, then the `qsteal` has been split up into the various steal results (empty/contended/success). `st_ctdd_max` gives the maximum amount of contended steal attempts in a row. `st_biasdrop` shows how many times the steal bias has been dropped (reset).
>> `ovflw-push` and `ovfl-max` are the same as before, just renamed a bit to use the available space.
>>
>> There has been no intention to change anything about the algorithm, so there is no need for perf testing (I can see). Later changes will do that.
>>
>> Thanks,
>> Thomas
>
> Thomas Schatzl has updated the pull request incrementally with two additional commits since the last revision:
>
> - Some further cleanup
> - kbarrett review
In need for a second reviewer... :)
-------------
PR: https://git.openjdk.java.net/jdk/pull/7143
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