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

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Message-ID: <20131114105017.GD543@linux.vnet.ibm.com>
Date:	Thu, 14 Nov 2013 16:20:17 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
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.

> +			/*
> +			 * 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)) {

Peter, 

Please do let me know if you agree and if you want to spin of a new
version?

> +				power_orig += power_of(cpu);
> +				power += power_of(cpu);
> +				continue;
> +			}
> +
> +			sgp = rq->sd->groups->sgp;
> +			power_orig += sgp->power_orig;
> +			power += sgp->power;
>  		}
>  	} else  {
>  		/*
> 

-- 
Thanks and Regards
Srikar Dronamraju

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