linux-kernel - Re: [tip:sched/urgent] sched: Fix select_idle_sibling() regression in selecting an idle SMT sibling

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Date:	Thu, 22 Dec 2011 14:59:34 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"efault@....de" <efault@....de>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Huang, Ying" <ying.huang@...el.com>
Subject: Re: [tip:sched/urgent] sched: Fix select_idle_sibling() regression
 in selecting an idle SMT sibling

On Thu, 2011-12-22 at 10:16 +0800, Alex,Shi wrote:
> On Thu, 2011-12-22 at 10:03 +0800, Siddha, Suresh B wrote:
> > On Wed, 2011-12-21 at 17:31 -0800, Shi, Alex wrote:
> > > This patch partly fixed a performance regression that triggered by
> > > 4dcfe1025b513c2c, but issue still exists.
> > 
> > So how much was the regression caused by the commit 4dcfe1025b513c2c and
> > how much did we recover with this fix I posted. If we are talking about
> > the regression caused by this single commit 4dcfe1025b513c2c, then I
> > don't know of any other related fixes other than the recent fix we
> > pushed upstream (ab2789213d224202237292d78aaa0c386c7b28b2).
> 
> A little complex for the whole thing. 
> on 4 sockets EX machine, 3~5% hackbench thread regression due to 4dcfe
> can be recovered by ab2789. 
> 
> But on 2 sockets SNB machine, 1024 clients loop netperf TCP-RR has about
> 9% regression. and your patch seem recover 2~3%. 

Got the scheduler part from tip tree by command "git diff v3.2-rc6
kernel/sched*" and apply it again 3.2-rc6. Peter's commit "Only queue
remote wakeups when crossing cache boundaries" was included. But testing
show no change for TCP-RR result.

> 
> And on a 2 sockets nhm, one of our private benchmark was impact much 20
> +% regression. that benchmark just run 4 process, each of process open a
> thread, and the thread tasks is to locate randomly pages and than read
> from 4 times/write 1 time data into a page.  The ab2789 commit seems no
> help our benchmark. 
> 
> 
> 
> 


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