linux-kernel - Re: [PATCH] x86,sched: Fix sched_smt_power

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Message-ID: <20120111035156.GB7988@dirshya.in.ibm.com>
Date:	Wed, 11 Jan 2012 09:22:01 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Youquan Song <youquan.song@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, akpm@...ux-foundation.org, stable@...r.kernel.org,
	arjan@...ux.intel.com, len.brown@...el.com, anhua.xu@...el.com,
	chaohong.guo@...el.com, Youquan Song <youquan.song@...ux.intel.com>
Subject: Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken

* Suresh Siddha <suresh.b.siddha@...el.com> [2012-01-10 11:01:13]:

> On Tue, 2012-01-10 at 22:21 +0530, Vaidyanathan Srinivasan wrote:
> > * Youquan Song <youquan.song@...el.com> [2012-01-10 11:54:26]:
> > 
> > > 
> > > > Youquan, As far as I know both the
> > > > sched_smt_power_savings/sched_mc_power_savings are broken for atleast an
> > > > year.
> > > > 
> > > > Have you checked the state of 'sched_mc_power_savings' to see if it is
> > > > working or gets addressed with your proposed patches?
> > > Thanks Suresh!
> > > 
> > > We have verified that sched_mc_power_savings works well in mainline and
> > > -tip tree, only sched_smt_power_savings broken.
> > 
> > Hi Suresh,
> > 
> > My testing also shows that sched_mc works find and only sched_smt
> > suffers from the group capacity problem at the core level.
> > 
> 
> No. I just checked and it doesn't work as intended.
> 
> On a 2 socket 8-core SMT system, I ran 8 cpu hoggers and just toggled
> 'sched_mc_power_savings' between 0 and 1 multiple times. Irrespective of
> the value, those 8 hoggers are distributed evenly between two sockets -
> 4 each and doesn't change their positions.
> 
> So I can bet it doesn't work.

Hi Suresh,

I had tested sched_mc_powersavings=2 on dual socket quad core HT
nehalem.  It worked as expected.  Let me check the
sched_mc_powersavings=1 case.  I will not be surprised if it is
broken.

--Vaidy

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