linux-kernel - RE: [patch 0/4] [RFC] Another proportional weight IO controller

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Message-Id: <1226649735.7685.6917.camel@twins>
Date:	Fri, 14 Nov 2008 09:02:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Satoshi UCHIDA <s-uchida@...jp.nec.com>
Cc:	'Vivek Goyal' <vgoyal@...hat.com>,
	'Nauman Rafique' <nauman@...gle.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org,
	virtualization@...ts.linux-foundation.org, jens.axboe@...cle.com,
	'Hirokazu Takahashi' <taka@...inux.co.jp>,
	'Ryo Tsuruta' <ryov@...inux.co.jp>,
	'Andrea Righi' <righi.andrea@...il.com>,
	fernando@....ntt.co.jp, balbir@...ux.vnet.ibm.com,
	'Andrew Morton' <akpm@...ux-foundation.org>, menage@...gle.com,
	ngupta@...gle.com, 'Rik van Riel' <riel@...hat.com>,
	'Jeff Moyer' <jmoyer@...hat.com>, dpshah@...gle.com,
	'Mike Waychison' <mikew@...gle.com>, rohitseth@...gle.com,
	'Fabio Checconi' <fchecconi@...il.com>,
	paolo.valente@...more.it
Subject: RE: [patch 0/4] [RFC] Another proportional weight IO controller

On Fri, 2008-11-14 at 13:58 +0900, Satoshi UCHIDA wrote:

> > I think Satoshi's cfq controller patches also do not seem to be considering
> > A, B, C, D and E to be at same level, instead it treats cgroup "/" , D and
> > E
> > at same level and tries to do proportional BW division among these.
> > Satoshi, please correct me, if that's not the case.
> > 
> 
> Yes.
> I think that a controller should be divided share among "/(root)" and two groups.
> This reason is follows:
> 
>   * If these tasks are handled at same level, it is enough by using a traditional 
>     CFQ scheduler.
>     If you want to make all tasks in the same group the same priority(parameter),
>     It is not I/O control but is parameter control.
>     
>   * I think that the group means the environment which makes some sense and 
>     user want to control I/O per groups.
>     Next, the group is the environment.  So, tasks within the group will have
>     priorities for themselves respectively as traditional environment.
>     Of course, group may not be need to control I/O.
>     In such time, a ioprio of tasks should be set the same priority.
> 
> Therefore, our scheduler controls among group and then among tasks

I would suggest abandoning this scheme as its different from how the CPU
scheduler does it. The CPU scheduler is fully hierarchical and tasks in
"/" are on the same level as groups in "/".

That is, we do:

      root
      / | \
     1  2  A
          / \
         B   3
        / \
       4   5

Where digits are tasks, and letters are groups.

Having the two bandwidth (CPU, I/O) doing different things wrt grouping
can only be confusing at best.


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