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Date: Wed, 09 Sep 2009 19:01:46 +0900 (JST)
From: Ryo Tsuruta <ryov@...inux.co.jp>
To: vgoyal@...hat.com
Cc: riel@...hat.com, linux-kernel@...r.kernel.org, dm-devel@...hat.com,
jens.axboe@...cle.com, agk@...hat.com, akpm@...ux-foundation.org,
nauman@...gle.com, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
balbir@...ux.vnet.ibm.com
Subject: Re: Regarding dm-ioband tests
Hi Vivek,
Vivek Goyal <vgoyal@...hat.com> wrote:
> > I think there are some advantages to dm-ioband. That's why I post
> > dm-ioband to the mailing list.
> >
> > - dm-ioband supports not only proportional weight policy but also rate
> > limiting policy. Besides, new policies can be added to dm-ioband if
> > a user wants to control bandwidth by his or her own policy.
>
> I think we can easily extent io scheduler based controller to also support
> max rate per group policy also. That should not be too hard. It is a
> matter of only keeping track of io rate per group and if a group is
> exceeding the rate, then schedule it out and move on to next group.
>
> I can do that once proportional weight solution is stablized and gets
> merged.
>
> So its not an advantage of dm-ioband.
O.K.
> > - The dm-ioband driver can be replaced without stopping the system by
> > using device-mapper's facility. It's easy to maintain.
>
> We talked about this point in the past also. In io scheduler based
> controller, just move all the tasks to root group and you got a system
> not doing any io control.
>
> By the way why would one like to do that?
>
> So this is also not an advantage.
My point is that dm-ioband can be updated for improvements and
bug-fixing without stopping the system.
> > - dm-ioband can use without cgroup. (I remember Vivek said it's not an
> > advantage.)
>
> I think this is more of a disadvantage than advantage. We have a very well
> defined functionality of cgroup in kernel to group the tasks. Now you are
> coming up with your own method of grouping the tasks which will make life
> even more confusing for users and application writers.
>
> I don't understand what is that core requirement of yours which is not met
> by io scheduler based io controller. range policy control you have
> implemented recently. I don't think that removing dm-ioband module
> dynamically is core requirement. Also whatever you can do with additional
> grouping mechanism, you can do with cgroup also.
>
> So if there is any of your core functionality which is not fulfilled by
> io scheduler based controller, please let me know. I will be happy to look
> into it and try to provide that feature. But looking at above list, I am
> not convinced that any of the above is a compelling argument for dm-ioband
> inclusion.
As I wrote in another email, I would like to make use of dm-ioband on
the system which doesn't support cgroup such as RHEL. In addition,
there are devices which doesn't use standard IO schedulers, and
dm-ioband can work on even such devices.
Thanks,
Ryo Tsuruta
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