linux-kernel - Re: Regarding dm-ioband tests

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Message-Id: <20090916.012128.71105809.ryov@valinux.co.jp>
Date:	Wed, 16 Sep 2009 01:21:28 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	balbir@...ux.vnet.ibm.com
Cc:	dhaval@...ux.vnet.ibm.com, vgoyal@...hat.com, 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
Subject: Re: Regarding dm-ioband tests

Hi Balbir,

Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> * Ryo Tsuruta <ryov@...inux.co.jp> [2009-09-16 00:12:37]:
> 
> > Hi Dhaval,
> > 
> > Dhaval Giani <dhaval@...ux.vnet.ibm.com> wrote:
> > > > Dhaval Giani <dhaval@...ux.vnet.ibm.com> wrote:
> > > > > > I know that cgroup is a very well defined functionality, that is why
> > > > > > dm-ioband also supports throttling per cgroup. But how are we supposed
> > > > > > to do throttling on the system which doesn't support cgroup?
> > > > > > As I wrote in another mail to Vivek, I would like to make use of
> > > > > > dm-ioband on RHEL 5.x. 
> > > > > 
> > > > > Hi Ryo,
> > > > > 
> > > > > I am not sure that upstream should really be worrying about RHEL 5.x.
> > > > > cgroups is a relatively mature solution and is available in most (if not
> > > > > all) community distros today. We really should not be looking at another
> > > > > grouping solution if the sole reason is that then dm-ioband can be used
> > > > > on RHEL 5.x. The correct solution would be to maintain a separate patch
> > > > > for RHEL 5.x then and not to burden the upstream kernel.
> > > > 
> > > > RHEL 5.x is not the sole reason for that.
> > > > 
> > > 
> > > Could you please enumerate the other reasons for pushing in another
> > > grouping mechanism then? (Why can we not resolve them via cgroups?)
> > 
> > I'm sorry for late reply.
> > 
> > I'm not only pushing in the grouping mechanism by using the dmsetup
> > command. Please understand that dm-ioband also provides cgroup
> > interface and can be configured in the same manner like other cgroup
> > subsystems.
> > Why it is so bad to have multiple ways to configure? I think that it
> > rather gains in flexibility of configurations.
> >
> 
> The main issue I see is user confusion and distro issues. If a distro
> compiles cgroups and dmsetup provides both methods, what method
> do we recommend to end users? Also should system management tool
> support two configuration mechanisms for the same functionality?

I think that it is up to users which mechanism they choose to use, and
such kind of users who can use dmsetup or cgroup interface directly
will not be confused in such a situation.

I also think that management tools are required for end users, and if
a distro supports cgroups, I recommend the management tools configure
dm-ioband by using cgroups, because dm-ioband is more usable when
using with blkio-cgroup and memory cgroup.

Thanks,
Ryo Tsuruta
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