linux-kernel - Re: [RFC tg_shares_up improvements - v1 05/12] sched: fix update_cfs

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Message-ID: <20101021095221.GC3581@in.ibm.com>
Date:	Thu, 21 Oct 2010 15:22:21 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	pjt@...gle.com
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Pierre Bourdon <pbourdon@...ellency.fr>
Subject: Re: [RFC tg_shares_up improvements - v1 05/12] sched: fix
	update_cfs_load synchronization

On Fri, Oct 15, 2010 at 09:43:54PM -0700, pjt@...gle.com wrote:
> Using cfs_rq->nr_running is not sufficient to synchronize update_cfs_load with
> the put path since nr_running accounting occurs at deactivation.
> 
> It's also not safe to make the removal decision based on load_avg as this fails
> with both high periods and low shares.  Resolve this by clipping history at 8
> foldings.
> 

Did you mean 4 foldings (and not 8) above since I see you are truncating
the load history at 4 idle periods ?


> @@ -685,9 +686,19 @@ static void update_cfs_load(struct cfs_r
>  	now = rq_of(cfs_rq)->clock;
>  	delta = now - cfs_rq->load_stamp;
> 
> +	/* truncate load history at 4 idle periods */
> +	if (cfs_rq->load_stamp > cfs_rq->load_last &&
> +	    now - cfs_rq->load_last > 4 * period) {
> +		cfs_rq->load_period = 0;
> +		cfs_rq->load_avg = 0;
> +	}
> +
>  	cfs_rq->load_stamp = now;
>  	cfs_rq->load_period += delta;
> -	cfs_rq->load_avg += delta * cfs_rq->load.weight;
> +	if (load) {
> +		cfs_rq->load_last = now;
> +		cfs_rq->load_avg += delta * load;
> +	}
> 
>  	while (cfs_rq->load_period > period) {
>  		/*
> @@ -700,10 +711,8 @@ static void update_cfs_load(struct cfs_r
>  		cfs_rq->load_avg /= 2;
>  	}
> 
> -	if (lb && !cfs_rq->nr_running) {
> -		if (cfs_rq->load_avg < (period / 8))
> -			list_del_leaf_cfs_rq(cfs_rq);
> -	}
> +	if (!cfs_rq->curr && !cfs_rq->nr_running && !cfs_rq->load_avg)
> +		list_del_leaf_cfs_rq(cfs_rq);
>  }
> 
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