linux-kernel - Re: [patch 2/3] sched: fix minimum power returned by update_cpu

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Date:	Mon, 16 Aug 2010 10:37:59 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"chris@...stnet.net" <chris@...stnet.net>,
	"debian00@...ceadsl.fr" <debian00@...ceadsl.fr>,
	"hpa@...or.com" <hpa@...or.com>,
	"jonathan.protzenko@...il.com" <jonathan.protzenko@...il.com>,
	"mans@...sr.com" <mans@...sr.com>,
	"psastudio@...l.ru" <psastudio@...l.ru>,
	"rjw@...k.pl" <rjw@...k.pl>,
	"stephan.eicher@....de" <stephan.eicher@....de>,
	"sxxe@....de" <sxxe@....de>,
	"thomas@...hlinux.org" <thomas@...hlinux.org>,
	"venki@...gle.com" <venki@...gle.com>,
	"wonghow@...il.com" <wonghow@...il.com>
Subject: Re: [patch 2/3] sched: fix minimum power returned by
 update_cpu_power()

On Mon, 2010-08-16 at 00:50 -0700, Peter Zijlstra wrote:
> On Fri, 2010-08-13 at 12:45 -0700, Suresh Siddha wrote:
> > plain text document attachment (fix_update_cpu_power.patch)
> > Default cpu_power needs to be multiples of SCHED_LOAD_SCALE and not '1'.
> > Fix it.
> > 
> > Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> > ---
> >  kernel/sched_fair.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Index: tree/kernel/sched_fair.c
> > ===================================================================
> > --- tree.orig/kernel/sched_fair.c
> > +++ tree/kernel/sched_fair.c
> > @@ -2309,7 +2309,7 @@ static void update_cpu_power(struct sche
> >  	power >>= SCHED_LOAD_SHIFT;
> >  
> >  	if (!power)
> > -		power = 1;
> > +		power = SCHED_LOAD_SCALE;
> >  
> 
>                             smt_power   freq_power    rt_power
> power = SCHED_LOAD_SCALE * ---------- * ---------- * ----------
>                            LOAD_SCALE   LOAD_SCALE   LOAD_SCALE
> 
> Which, in the above case ends up being 0, so how does resetting it back
> to LOAD_SCALE make sense?

hmm, true, but I thought I saw some load balancing code which was
depending on SCHED_LOAD_SCALE value. Ignore this for now. Will get back
to you if this indeed is a problem.

thanks,
suresh

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