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

From: Mike Galbraith <bitbucket@online.de>
To: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com,
	peterz@infradead.org, mingo@kernel.org, a.p.zijlstra@chello.nl
Subject: Re: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()
Date: Wed, 23 Jan 2013 10:37:04 +0100	[thread overview]
Message-ID: <1358933824.5752.136.camel@marge.simpson.net> (raw)
In-Reply-To: <50FFACC5.7060405@linux.vnet.ibm.com>

On Wed, 2013-01-23 at 17:26 +0800, Michael Wang wrote: 
> On 01/23/2013 05:18 PM, Mike Galbraith wrote:
> > On Wed, 2013-01-23 at 17:00 +0800, Michael Wang wrote: 
> >> On 01/23/2013 04:49 PM, Mike Galbraith wrote:
> >>> On Wed, 2013-01-23 at 16:30 +0800, Michael Wang wrote: 
> >>>> On 01/23/2013 04:20 PM, Mike Galbraith wrote:
> >>>>> On Wed, 2013-01-23 at 15:10 +0800, Michael Wang wrote: 
> >>>>>> On 01/23/2013 02:28 PM, Mike Galbraith wrote:
> >>>>>
> >>>>>>> Abbreviated test run:
> >>>>>>> Tasks    jobs/min  jti  jobs/min/task      real       cpu
> >>>>>>>   640   158044.01   81       246.9438     24.54    577.66   Wed Jan 23 07:14:33 2013
> >>>>>>>  1280    50434.33   39        39.4018    153.80   5737.57   Wed Jan 23 07:17:07 2013
> >>>>>>>  2560    47214.07   34        18.4430    328.58  12715.56   Wed Jan 23 07:22:36 2013
> >>>>>>
> >>>>>> So still not works... and not going to balance path while waking up will
> >>>>>> fix it, looks like that's the only choice if no error on balance path
> >>>>>> could be found...benchmark wins again, I'm feeling bad...
> >>>>>>
> >>>>>> I will conclude the info we collected and make a v3 later.
> >>>>>
> >>>>> FWIW, I hacked virgin to do full balance if an idle CPU was not found,
> >>>>> leaving the preference to wake cache affine intact though, turned on
> >>>>> WAKE_BALANCE in all domains, and it did not collapse.  In fact, the high
> >>>>> load end, where the idle search will frequently be a waste of cycles,
> >>>>> actually improved a bit.  Things that make ya go hmmm.
> >>>>
> >>>> Oh, does that means the old balance path is good while the new is really
> >>>> broken, I mean, compared this with the previously results, could we say
> >>>> that all the collapse was just caused by the change of balance path?
> >>>
> >>> That's a good supposition.  I'll see if it holds.
> >>
> >> I just notice that there is no sd support the WAKE flag at all according
> >> to your debug info, isn't it?
> > 
> > There is, I turned it on in all domains.

? Virgin doesn't have any of your patches.  In virgin, I can twiddle
flags effectively with a script.

With your patches, I have to make that happen from the start for it to
be effective, but not in virgin (well nearly virgin) 3.8-rc3.

-Mike