linux-kernel - Re: change in sched cpu_power causing regressions with SCHED

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Date:	Fri, 19 Feb 2010 20:52:12 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Ma, Ling" <ling.ma@...el.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	"ego@...ibm.com" <ego@...ibm.com>,
	"svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com>
Subject: Re: change in sched cpu_power causing regressions with SCHED_MC

On Fri, 2010-02-19 at 10:36 -0800, Suresh Siddha wrote:
> > About the ping-pong for the statically infeasible scenario, the problem
> > with that is that we actually want to ping-pong a little [*], so we
> > might want to look at maybe doing a sd->next_pingpong jiffy measure to
> > allow some of that.
> > 
> > [*] I've seen people pretty upset about the fact that when they start 6
> > similar loads on a quad cpu the tasks will not finish in roughly similar
> > times.
> 
> I thought we were doing this (ping-ping a little) already. Unless
> something broke here also. I thought fix_small_imbalance() takes care of
> this too. 

I'm not sure we do, when I test on the patched kernel I see two distinct
groups of runtime appear (haven't checked the unpatched one, but I doubt
it'll be better).



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