linux-kernel - Re: [PATCH 2/3] sched/fair: Move hot load

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Message-ID: <20151130102322.GI17308@twins.programming.kicks-ass.net>
Date:	Mon, 30 Nov 2015 11:23:22 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <Waiman.Long@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH 2/3] sched/fair: Move hot load_avg into its own cacheline

On Wed, Nov 25, 2015 at 02:09:39PM -0500, Waiman Long wrote:
> +++ b/kernel/sched/sched.h
> @@ -248,7 +248,12 @@ struct task_group {
>  	unsigned long shares;
>  
>  #ifdef	CONFIG_SMP
> -	atomic_long_t load_avg;
> +	/*
> +	 * load_avg can be heavily contended at clock tick time, so put
> +	 * it in its own cacheline separated from the fields above which
> +	 * will also be accessed at each tick.
> +	 */
> +	atomic_long_t load_avg ____cacheline_aligned;

Same as with the other patch; this only works if the structure itself is
cacheline aligned, which I don't think it is.

>  #endif
>  #endif
>  
> -- 
> 1.7.1
> 
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