linux-kernel - Re: [PATCH v2 0/3]CFQ: add think time check for service tree and group

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Date:	Tue, 12 Jul 2011 08:15:13 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Jens Axboe <jaxboe@...ionio.com>
Subject: Re: [PATCH v2 0/3]CFQ: add think time check for service tree and
 group

On Tue, Jul 12, 2011 at 09:37:52AM +0800, Shaohua Li wrote:
> Hi,
>   Currently when the last queue of a service tree/group is empty, CFQ
> doesn't expire the queue. This is to allow requests from the tree/group
> come soon, so tree/group doesn't miss its share. But if the think time
> is big, the assumption isn't correct. idling the queue is just wasting
> bandwidth.
> 
> Originally I was hoping this can resolve Vivek's fsync issue, but it
> doesn't. The fsync issue is caused by queue idling. But since think time
> check only helps for think time above default queue idle time (8ms),
> think time check doesn't help for the fsync issue.
> 
> On the other hand, think time check is still helpful for queues with
> think time. I had test case in follow patches show throughput
> improvement without sacrifice tree/group shares.
> 
> v1->v2:
> 1. addressed some good comments from Vivek
> 2. add more test to make sure the patches don't change behavior of
> queues without think time.

This patch series looks good to me. Thanks Shaohua. We still shall have
to do something about fsync issue though in groups.

Acked-by: Vivek Goyal <vgoyal@...hat.com>

Thanks
Vivek
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