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SubjectRe: CFS review
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Ingo Molnar wrote:
> * Al Boldi <a1426z@gawab.com> wrote:
> > > could you send the exact patch that shows what you did?
> >
> > On 2.6.22.5-v20.3 (not v20.4):
> >
> > 340- curr->delta_exec += delta_exec;
> > 341-
> > 342- if (unlikely(curr->delta_exec > sysctl_sched_stat_granularity))
> > { 343:// __update_curr(cfs_rq, curr);
> > 344- curr->delta_exec = 0;
> > 345- }
> > 346- curr->exec_start = rq_of(cfs_rq)->clock;
>
> ouch - this produces a really broken scheduler - with this we dont do
> any run-time accounting (!).

Of course it's broken, and it's not meant as a fix, but this change allows
you to see the amount of overhead as well as any miscalculations
__update_curr incurs.

In terms of overhead, __update_curr incurs ~3x slowdown, and in terms of
run-time accounting it exhibits a ~10sec task-startup miscalculation.

> Could you try the patch below instead, does this make 3x glxgears smooth
> again? (if yes, could you send me your Signed-off-by line as well.)

The task-startup stalling is still there for ~10sec.

Can you see the problem on your machine?


Thanks!

--
Al

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