linux-kernel - Re: [RFC V2 PATCH 1/5] cfq-iosched: adapt slice to number of processes doing I/O

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Date:	Mon, 26 Oct 2009 16:14:57 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC V2 PATCH 1/5] cfq-iosched: adapt slice to number of 
	processes doing I/O

On Mon, Oct 26, 2009 at 4:10 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Corrado Zoccolo <czoccolo@...il.com> writes:
>>
>> What about:
>> /* interested queues (we consider only the ones with the same priority class) */
>> unsigned iq = cfq_get_avg_queues(cfqd, cfq_class_rt(cfqq));
>> unsigned sync_slice = cfqd->cfq_slice[1];
>> unsigned expected_latency = sync_slice * iq;
>> if (expected_latency > target_latency) {
>>       unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
>>       /* scale low_slice according to IO priority and sync vs async */
>>       unsigned low_slice = min(slice,  base_low_slice * slice / sync_slice);
>>       /* the adapted slice value is scaled to fit all iqs into the target latency */
>>       slice = max(slice * cfq_target_latency / expected_latency, low_slice);
>> }
>
> Yeah, that looks a ton better.  Thanks for doing that!

Jens, if you like the new version of the code (integrating this last
change), I can rebase my patch set on top of Jeff's, since it is
already queued for 2.6.33 .

Corrado

>
> Cheers,
> Jeff
>
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