linux-kernel - Re: [PATCH]cfq-iosched: don't take requests with long distence as close

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Message-ID: <4e5e476b1001151224x5c94382cnf2a6696f10c9800d@mail.gmail.com>
Date:	Fri, 15 Jan 2010 21:24:23 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Shaohua Li <shaohua.li@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>
Subject: Re: [PATCH]cfq-iosched: don't take requests with long distence as 
	close

On Fri, Jan 15, 2010 at 8:45 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Corrado Zoccolo <czoccolo@...il.com> writes:
>
>> Hi Jeff,
>> I think this patch has the same flaw as Shaohua's.
>> The seekiness check that you introduce in cfq_rq_close is already
>> present in its caller, cfq_close_cooperator, so it is not effective.
>
> I don't think so.  There are two queues, here.  One queue is checked by
> the caller, and that is the cur_cfqq.  The __cfqq needs to also be
> checked.
The other one, i.e. the returned one, is also checked by the caller,
some lines below.
1756         cfqq = cfqq_close(cfqd, cur_cfqq);
1757         if (!cfqq)
1758                 return NULL;
1759
1760         /* If new queue belongs to different cfq_group, don't choose it */
1761         if (cur_cfqq->cfqg != cfqq->cfqg)
1762                 return NULL;
1763
1764         /*
1765          * It only makes sense to merge sync queues.
1766          */
1767         if (!cfq_cfqq_sync(cfqq))
1768                 return NULL;
1769         if (CFQQ_SEEKY(cfqq))
1770                 return NULL;
>
>> Up to now, the only patch that improves this situation is the one that
>> changes the unmerge policy to unmerge after a single time slice.
>
> Yes, I definitely agree with that, and I think that patch should go in.
>
> Cheers,
> Jeff
>



-- 
__________________________________________________________________________

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