linux-kernel - Re: [PATCH v2] sched: Check sched_domain before computing group power.

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Message-ID: <20131114111514.GH16796@laptop.programming.kicks-ass.net>
Date:	Thu, 14 Nov 2013 12:15:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mikey@...ling.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [PATCH v2] sched: Check sched_domain before computing group
 power.

On Thu, Nov 14, 2013 at 04:20:17PM +0530, Srikar Dronamraju wrote:
> > +			/*
> > +			 * build_sched_domains() -> init_sched_groups_power()
> > +			 * gets here before we've attached the domains to the
> > +			 * runqueues.
> > +			 *
> > +			 * Use power_of(), which is set irrespective of domains
> > +			 * in update_cpu_power().
> > +			 *
> > +			 * This avoids power/power_orig from being 0 and
> > +			 * causing divide-by-zero issues on boot.
> > +			 *
> > +			 * Runtime updates will correct power_orig.
> > +			 */
> > +			if (!rq->sd) {
> 
> Because this condition is only true during boot up, I am now
> thinking if we should do mark this as unlikely i.e if (unlikely(!rq->sd)) {

Makes sense, edited the patch.

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