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Date:	Wed, 13 Jan 2010 16:23:22 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"guijianfeng@...fujitsu.com" <guijianfeng@...fujitsu.com>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH]cfq-iosched: don't stop async queue with async requests
 pending

On Wed, Jan 13, 2010 at 04:18:47PM +0800, Corrado Zoccolo wrote:
> On Wed, Jan 13, 2010 at 8:44 AM, Shaohua Li <shaohua.li@...el.com> wrote:
> > My SSD speed of direct write is about 80m/s, while I test page writeback,
> > the speed can only go to 68m/s. Below patch fixes this.
> > It appears we missused cfq_should_idle in cfq_may_dispatch. cfq_should_idle
> > means a queue should idle because it's seekless sync queue or it's the last queue,
> > which is to maintain service tree time slice. So it doesn't mean the
> > last queue is always a sync queue. If the last queue is asyn queue,
> > we definitely shouldn't stop dispatch requests because of pending async
> > requests.
> 
> An other option is that cfq_should_idle returns false for async
> queues, since cfq will never idle on them.
I'm considering this option too, but it appears we need make async queue
idle to maintain domain time slice.

Thanks,
Shaohua
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