On 2014-11-10 07:19, Vasily Tarasov wrote:
Hi Jens,
td->start is used in __show_running_run_stats() to compute the time
that passed since the beginning of the loop (stored in td->start) to
the moment when periodical statistics need to be printed. Then
td->ts.runtime[] is temporarily updated based on the computed value.
In thread_main(), similar actions are taken to update td->ts.runtime[]
based on the td->start and the loop's elapsed time. Without the patch,
td->start is set in the very beginning of the loop in thread_main().
So, it leaves a time window between the end of the current loop and
the beginning of the next loop when td->ts.runtime[] is already
updated while td->start still stores the start of the previous lop. If
__show_running_run_stats() is called during that window - the time can
be (temporarily) added twice to td->ts.runtime[].
However, if we reset the start time in the end of the loop under the
stat_mutex it should not happen.
I would agree that having a per-td mutex might be an overkill
considering that people usually print statistics periodically with
relatively long intervals: 1, 5, 10, 60 seconds.
Thanks, I missed the change in addition after IO was done, hence the
question on ->start. I did commit the patch as-is yesterday, thanks!
--
Jens Axboe
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