Re: [PATCH] sched: wakeup buddy

[Mike Galbraith <efault@gmx.de>]

On Thu, 2013-03-07 at 09:36 +0100, Peter Zijlstra wrote: 
> On Wed, 2013-03-06 at 15:06 +0800, Michael Wang wrote:
> 
> > wake_affine() stuff is trying to bind related tasks closely, but it doesn't
> > work well according to the test on 'perf bench sched pipe' (thanks to Peter).
> 
> so sched-pipe is a poor benchmark for this.. 
> 
> Ideally we'd write a new benchmark that has some actual data footprint
> and we'd measure the cost of tasks being apart on the various cache
> metrics and see what affine wakeup does for it.
> 
> Before doing something like what you're proposing, I'd have a hard look
> at WF_SYNC, it is possible we should disable/fix select_idle_sibling
> for sync wakeups.

If nobody beats me to it, I'm going to try tracking shortest round trip
to idle, and use a multiple of that to shut select_idle_sibling() down.
If avg_idle approaches round trip time, there's no win to be had, we're
just wasting cycles.

-Mike