Re: sched: tweak select_idle_sibling to look for idle threads

[Chris Mason]

On Sun, Apr 10, 2016 at 12:04:21PM +0200, Mike Galbraith wrote:
> On Sat, 2016-04-09 at 15:05 -0400, Chris Mason wrote:
> 
> > This does preserve the existing logic to prefer idle cores over idle
> > CPU threads, and includes some tests to try and avoid the idle scan when we're
> > actually better off sharing a non-idle CPU with someone else.
> 
> My box says the "oh nevermind" checks aren't selective enough, tbench
> dropped 4% at clients=cores, and 2% at clients=threads.

Ok, I was able to reproduce this by stuffing tbench_srv and tbench onto
just socket 0.  Version 2 below fixes things for me, but I'm hoping
someone can suggest a way to get task_hot() buddy checks without the rq
lock.

I haven't run this on production loads yet, but our 4.0 patch for this
uses task_hot(), so I'd expect it to be on par.  If this doesn't fix it
for you, I'll dig up a similar machine on Monday.

-chris