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[dm-devel] Re: IO scheduler based IO Controller V2

Hi Vivek,

From: Vivek Goyal <vgoyal redhat com>
Subject: Re: IO scheduler based IO Controller V2
Date: Wed, 6 May 2009 21:25:59 -0400

> On Thu, May 07, 2009 at 09:18:58AM +0900, Ryo Tsuruta wrote:
> > Hi Vivek,
> > 
> > > Ryo, dm-ioband breaks the notion of classes and priority of CFQ because
> > > of FIFO dispatch of buffered bios. Apart from that it tries to provide
> > > fairness in terms of actual IO done and that would mean a seeky workload
> > > will can use disk for much longer to get equivalent IO done and slow down
> > > other applications. Implementing IO controller at IO scheduler level gives
> > > us tigher control. Will it not meet your requirements? If you got specific
> > > concerns with IO scheduler based contol patches, please highlight these and
> > > we will see how these can be addressed.
> > 
> > I'd like to avoid making complicated existing IO schedulers and other
> > kernel codes and to give a choice to users whether or not to use it.
> > I know that you chose an approach that using compile time options to
> > get the same behavior as old system, but device-mapper drivers can be
> > added, removed and replaced while system is running.
> > 
> Same is possible with IO scheduler based controller. If you don't want
> cgroup stuff, don't create those. By default everything will be in root
> group and you will get the old behavior. 
> If you want io controller stuff, just create the cgroup, assign weight
> and move task there. So what more choices do you want which are missing
> here?

What I mean to say is that device-mapper drivers can be completely
removed from the kernel if not used.

I know that dm-ioband has some issues which can be addressed by your
IO controller, but I'm not sure your controller works well. So I would
like to see some benchmark results of your IO controller.

Ryo Tsuruta

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