Re: Volanomark slows by 80% under CFS

Rik van Riel
2007-07-28T02:48:06Z

Tim Chen wrote:
> Ingo,
>
> Volanomark slows by 80% with CFS scheduler on 2.6.23-rc1.
> Benchmark was run on a 2 socket Core2 machine.
>
> The change in scheduler treatment of sched_yield
> could play a part in changing Volanomark behavior.
> In CFS, sched_yield is implemented
> by dequeueing and requeueing a process . The time a process
> has spent running probably reduced the the cpu time due it
> by only a bit. The process could get re-queued pretty close
> to head of the queue, and may get scheduled again pretty
> quickly if there is still a lot of cpu time due.

I wonder if this explains the 30% drop in top performance
seen with the MySQL sysbench benchmark when the scheduler
changed to CFS...

See http://people.freebsd.org/~jeff/sysbench.png

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