linux-kernel - Re: dm-ioband: Test results.

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Message-ID: <49EE69C2.9030908@cn.fujitsu.com>
Date:	Wed, 22 Apr 2009 08:50:10 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Mike Snitzer <snitzer@...hat.com>,
	device-mapper development <dm-devel@...hat.com>,
	nauman@...gle.com, fernando@....ntt.co.jp,
	linux-kernel@...r.kernel.org, jmoyer@...hat.com,
	jens.axboe@...cle.com, agk@...hat.com, balbir@...ux.vnet.ibm.com
Subject: Re: dm-ioband: Test results.

Vivek Goyal wrote:
> On Tue, Apr 21, 2009 at 09:57:23AM -0400, Mike Snitzer wrote:
>> On Tue, Apr 21 2009 at  8:10am -0400,
>> Ryo Tsuruta <ryov@...inux.co.jp> wrote:
>>
>>> Hi Nauman,
>>>
>>>>> The real question is, once you create a version of dm-ioband that
>>>>> co-operates with CFQ scheduler, how that solution would compare with
>>>>> the patch set Vivek has posted? In my opinion, we need to converge to
>>>>> one solution as soon as possible, so that we can work on it together
>>>>> to refine and test it.
>>>> I think I can do some help for your work. but I want to continue the
>>>> development of dm-ioband, because dm-ioband actually works well and
>>>> I think it has some advantages against other IO controllers.
>>>>   - It can use without cgroup.
>>>>   - It can control bandwidth on a per partition basis.
>>>>   - The driver module can be replaced without stopping the system.
>>> In addition, dm-ioband can run on the RHEL5.
>> RHEL5 compatibility does not matter relative to merging an I/O bandwidth
>> controller upstream.  So both the "can [be] use without cgroup" and "can
>> run on RHEL5" features do not help your cause of getting dm-ioband
>> merged upstream.  In fact these features serve as distractions.
> 
> Exactly. I don't think that "it can be used without cgroup" is a feature
> or advantage. To me it is a disadvantage and should be fixed. cgroup is
> standard mechanism to group tasks arbitrarily and we should use that to make
> things working instead of coming up with own ways of grouping things and
> terming it as advantage.
> 

I agree. And for the case of cpu scheduler, there are user group scheduler
and cgroup group scheduler, but Peter said he would like to see user group
scheduler to be removed.

> What do you mean by "The driver module can be replaced without stopping
> the system"? I guess you mean that one does not have to reboot the system
> to remove ioband device? So if one decides to not use the cgroup, then
> one shall have to remove the ioband devices, remount the filesystems and
> restart the application?
> 
> With cgroup approach, if one does not want things to be classified, a user
> can simply move all the tasks to root group and things will be fine. No
> remounting, no application stopping etc. So this also does not look like
> an advantage instead sounds like an disadvantage.
> 
> Thanks
> Vivek
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