Re: [patch 2/2] sched: fix select_idle_sibling() logic inselect_task_rq_fair()

From: Mike Galbraith
Date: Sat Mar 06 2010 - 03:22:26 EST

On Fri, 2010-03-05 at 21:25 +0100, Mike Galbraith wrote:
> On Fri, 2010-03-05 at 10:39 -0800, Suresh Siddha wrote:
> > c) Also, selelct_idle_sibling() should also treat the current cpu as an idle
> > cpu if it is a sync wakeup and we have only one task running.
> I'm going to have to crawl over and test the above, but this bit sounds
> like a decidedly un-good thing to do. Maybe I'm misunderstanding.

Nope, no misunderstanding. This patch does kill throughput gains. Once
awakened affine, always awaken affine is a bad idea.

I dug up my old P4 though. With it's wimpy siblings, the cost of
running two schedulers doesn't appear to be generally worth it at a
glance. You need considerable overlap to break even.


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