linux-kernel - Re: [patch]cfq-iosched: schedule dispatch for noidle queue

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Date:	Tue, 21 Sep 2010 07:29:56 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"jaxboe@...ionio.com" <jaxboe@...ionio.com>,
	"czoccolo@...il.com" <czoccolo@...il.com>
Subject: Re: [patch]cfq-iosched: schedule dispatch for noidle queue

On Mon, 2010-09-20 at 22:02 +0800, Vivek Goyal wrote:
> On Mon, Sep 20, 2010 at 04:53:37PM +0800, Shaohua Li wrote:
> > A queue is idle at cfq_dispatch_requests(), but it gets noidle later for
> > different reasons. Unless other task explictly does unplug or all requests
> > are drained, we will not deliever requests to the disk even cfq_arm_slice_timer
> > doesn't make the queue idle. For example, cfq_should_idle() returns true
> > because of service_tree->count == 1, and then other queues are added.
> > Note, I didn't see obvious performance impacts so far with the patch, but
> > just thought this could be a problem.
> > 
> 
> Shaohua Li,
> 
> What are those reasons when an idling queue becomes a non idle one
> (without getting a new request in the queue)?
OOps, I used to add a new reason for another patch but forgot to update
the comment. So this is the only reason.

Thanks,
Shaohua

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