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

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Date:	Tue, 8 Dec 2009 21:46:39 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jeff Moyer <jmoyer@...hat.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

Hi Jeff,
On Tue, Dec 8, 2009 at 7:00 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> 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?

Previously, when cfq started, it started in a state where writes were
completely throttled. Now, we optimistically prefer to start with a
reasonable max depth (10)

Thanks
Corrado

> Cheers,
> Jeff
>



-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@...il.com
PhD - Department of Computer Science - University of Pisa, Italy
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