Re: [patch] sched: minimalist select_idle_sibling() bouncing cow syndrome fix

Ingo Molnar
2013-01-28T11:21:52Z

* Mike Galbraith <bitbucket@online.de> wrote:

> On Mon, 2013-01-28 at 11:53 +0100, Ingo Molnar wrote:
> > * Mike Galbraith <bitbucket@online.de> wrote:
> >
> > > If the previous CPU is cache affine and idle, select it.
> >
> > No objections in principle - but would be nice to have a
> > changelog with numbers, % of improvement included and so?
>
> Well, that like was my changelog, guess it needs improvement.
>
> Take 2.
>
> sched: minimalist select_idle_sibling() bouncing cow syndrome fix
>
> If the previous CPU is cache affine and idle, select it.
>
> The current implementation simply traverses the sd_llc domain,
> taking the first idle CPU encountered, which walks buddy pairs
> hand in hand over the package, inflicting excruciating pain.
>
> 1 tbench pair (worst case) in a 10 core + SMT package:
>
> pre 15.22 MB/sec 1 procs
> post 252.01 MB/sec 1 procs

Drool ... :-)

What would be a 'contrarian' test - i.e. a test where this could
hurt most?

Thanks,

Ingo