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Message-Id: <20090908.120119.71095369.ryov@valinux.co.jp>
Date: Tue, 08 Sep 2009 12:01:19 +0900 (JST)
From: Ryo Tsuruta <ryov@...inux.co.jp>
To: riel@...hat.com
Cc: vgoyal@...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 Rik,
Rik van Riel <riel@...hat.com> wrote:
> Ryo Tsuruta wrote:
>
> > However, if you want to get fairness in a case like this, a new
> > bandwidth control policy which controls accurately according to
> > assigned weights can be added to dm-ioband.
>
> Are you saying that dm-ioband is purposely unfair,
> until a certain load level is reached?
Not unfair, dm-ioband(weight policy) is intentionally designed to
use bandwidth efficiently, weight policy tries to give spare bandwidth
of inactive groups to active groups.
> > We regarded reducing throughput loss rather than reducing duration
> > as the design of dm-ioband. Of course, it is possible to make a new
> > policy which reduces duration.
>
> ... while also reducing overall system throughput
> by design?
I think it reduces system throughput compared to the current
implementation, because it causes more overhead to do fine grained
control.
> Why are you even bothering to submit this to the
> linux-kernel mailing list, when there is a codebase
> available that has no throughput or fairness regressions?
> (Vivek's io scheduler based io controler)
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.
- The dm-ioband driver can be replaced without stopping the system by
using device-mapper's facility. It's easy to maintain.
- dm-ioband can use without cgroup. (I remember Vivek said it's not an
advantage.)
Thanks,
Ryo Tsuruta
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