linux-kernel - Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed

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Message-ID: <x49hbs1fir5.fsf@segfault.boston.devel.redhat.com>
Date:	Tue, 08 Dec 2009 13:00:46 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	"Linux-Kernel" <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed

Corrado Zoccolo <czoccolo@...il.com> writes:

> The introduction of ramp-up formula for async queue depths has
> slowed down dirty page reclaim, by reducing async write performance.
> This patch makes sure the formula kicks in only when sync request
> was recently delayed.
> @@ -3706,7 +3707,7 @@ static void *cfq_init_queue(struct request_queue *q)
>  	cfqd->cfq_latency = 1;
>  	cfqd->cfq_group_isolation = 0;
>  	cfqd->hw_tag = -1;
> -	cfqd->last_end_sync_rq = jiffies;
> +	cfqd->last_delayed_sync = jiffies - HZ;

So, umm, what's that about?

Cheers,
Jeff
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