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

[Mike Galbraith]

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.

	-Mike

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/