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

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Message-ID: <1326222073.6283.9.camel@sbsiddha-mobl2>
Date:	Tue, 10 Jan 2012 11:01:13 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	svaidy@...ux.vnet.ibm.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

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.

thanks,
suresh

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