linux-kernel - Re: [dm-devel] Re: dm-ioband: Test results.

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Message-Id: <20090421.211827.39163016.ryov@valinux.co.jp>
Date:	Tue, 21 Apr 2009 21:18:27 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	vgoyal@...hat.com
Cc:	nauman@...gle.com, fernando@....ntt.co.jp,
	linux-kernel@...r.kernel.org, jmoyer@...hat.com,
	dm-devel@...hat.com, jens.axboe@...cle.com, agk@...hat.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com
Subject: Re: [dm-devel] Re: dm-ioband: Test results.

Hi Vivek,

> > I could see the priority inversion by running Vivek's script and I
> > understand how RT requests has to be handled. I'll create a patch
> > which makes dm-ioband cooperates with CFQ scheduler. However, do you
> > think we need some kind of limitation on processes which belong to the
> > RT class to prevent the processes from depleting bandwidth?
>
> I think to begin with, we can keep the same behavior as CFQ. An RT task
> can starve other tasks.
> 
> But we should provide two configurations and user can choose any one.
> If RT task is in root group, it will starve other sibling tasks/groups. If
> it is with-in a cgroup, then it will starve its sibling only with-in that
> cgroup and will not impact other cgroups.
> 
> What I mean is following.
> 
> 			root
> 			/  \
> 		      RT   group1
> 
> In above configuration RT task will starve everybody else.
> 
> 			root
> 		        /   \
> 		   group1   group2
> 		   /  \
> 	         RT   BE
> 
> In above configuration  RT task will starve only sibling in group1 but
> will not starve the tasks in group2 or in root.

Thanks for the suggestion. I'll try this way when dm-ioband supports
hierarchical grouping.

Thanks,
Ryo Tsuruta
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