linux-kernel - Re: [PATCH 18/21] blkcg: move blkio_group

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Message-ID: <4F7A2B21.5000907@tao.ma>
Date:	Tue, 03 Apr 2012 06:41:37 +0800
From:	Tao Ma <tm@....ma>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Tejun Heo <tj@...nel.org>, axboe@...nel.dk, ctalbott@...gle.com,
	rni@...gle.com, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [PATCH 18/21] blkcg: move blkio_group_conf->weight to cfq

On 04/03/2012 06:25 AM, Vivek Goyal wrote:
> On Tue, Apr 03, 2012 at 06:20:10AM +0800, Tao Ma wrote:
> 
> [..]
>>> Yeah, just add config and stat files prefixed with the name of the new
>>> blkcg policy.
>> OK, I will add a new config file for it.
> 
> Only if CFQ could be modified to add one iops mode, flippable through a
> sysfs tunable, things will be much simpler. You will not have to add a
> new IO scheduler, no new configuration/stat files in blkcg (which is
> already crowded now).
> 
> I don't think anybody has shown the code that why CFQ can't be modified
> to support iops mode.
Yes, I have thought of it, but it seems to me that time slice is deeply
involved within the cfq(even current cfq's iops mode has used time slice
to calculate). So I don't think it is feasible for me to change it. And
cfq works perfectly well for sas/sata environment and the code is quite
stable, more codes and more complicate algorithm does mean more bugs. So
I guess a new iops based scheduler is easy and not intrusive for the
user(since he can choose whether to use it or not).

Thanks
Tao
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