linux-kernel - Re: Regarding dm-ioband tests

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Date:	Wed, 09 Sep 2009 15:05:11 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	dhaval@...ux.vnet.ibm.com
Cc:	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,
	balbir@...ux.vnet.ibm.com
Subject: Re: Regarding dm-ioband tests

Hi,

Dhaval Giani <dhaval@...ux.vnet.ibm.com> wrote:
> > > - 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 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. 
And I don't think that the grouping methods are not complicated, just
stack a new device on the existing device and assign bandwidth to it,
that is the same method as other device-mapper targets, if you would
like to assign bandwidth per thread, then register the thread's ID to
the device and assign bandwidth to it as well. I don't think it makes
users confused.

> I would tend to agree with this. With other resource management
> controllers using cgroups, having dm-ioband use something different will
> require a different set of userspace tools/libraries to be used.
> Something that will severly limit its usefulness froma programmer's
> perspective.

Once we create a dm-ioband device, the device can be configured
through the cgroup interface. I think it will not severly limit its
usefulness.

Thanks,
Ryo Tsuruta
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