Re: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()

[Mike Galbraith <bitbucket@online.de>]

On Mon, 2013-01-21 at 10:44 +0100, Mike Galbraith wrote: 
> On Mon, 2013-01-21 at 17:22 +0800, Michael Wang wrote: 
> > On 01/21/2013 05:09 PM, Mike Galbraith wrote:
> > > On Mon, 2013-01-21 at 15:45 +0800, Michael Wang wrote: 
> > >> On 01/21/2013 03:09 PM, Mike Galbraith wrote:
> > >>> On Mon, 2013-01-21 at 07:42 +0100, Mike Galbraith wrote: 
> > >>>> On Mon, 2013-01-21 at 13:07 +0800, Michael Wang wrote:
> > >>>
> > >>>>> May be we could try change this back to the old way later, after the aim
> > >>>>> 7 test on my server.
> > >>>>
> > >>>> Yeah, something funny is going on.
> > >>>
> > >>> Never entering balance path kills the collapse.  Asking wake_affine()
> > >>> wrt the pull as before, but allowing us to continue should no idle cpu
> > >>> be found, still collapsed.  So the source of funny behavior is indeed in
> > >>> balance_path.
> > >>
> > >> Below patch based on the patch set could help to avoid enter balance path
> > >> if affine_sd could be found, just like the old logical, would you like to
> > >> take a try and see whether it could help fix the collapse?
> > > 
> > > No, it does not.
> > 
> > Hmm...what have changed now compared to the old logical?
> 
> What I did earlier to confirm the collapse originates in balance_path is
> below.  I just retested to confirm.

...

And you can add..

if (per_cpu(sd_llc_id, cpu) == per_cpu(sd_llc_id, prev_cpu))
goto unlock;

..before calling select_idle_sibling() the second time to optimize
department of redundancy department idle search algorithm ;-)

-Mike