On Wed, Jun 22, 2011 at 08:06:23PM +0800, Andrew Xu wrote:
>
> On Tue, 21 Jun 2011 09:33:37 -0400
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
>
> > On Tue, Jun 21, 2011 at 04:29:35PM +0800, Andrew Xu wrote:
> > > Hi all,
> > >
> > > I add a blkback QoS patch.
> >
> > What tree is this against?
> This patch is based on suse11.sp1(2.6.32) xen-blkback source.
> (2.6.18 "Xenlinux" based source trees?)
>
> > There is a xen-blkback in 3.0-rc4, can you rebase
> > it against that please.
> >
> Ok, I will rebase it.
Hold on, lets talk about the problem you are trying to solve first.
>
> > What is the patch solving?
> >
> With this path, you can set different speed I/O for different VM disk.
> For example, I set vm17-disk1 4MKB/s
> vm17-disk2 1MKB/s
> vm18-disk3 3MKB/s
> I/O speed, by writing follow xenstore key-values.
> /local/domain/17/device/vbd/768/tokens-rate = "4096"
> /local/domain/17/device/vbd/2048/tokens-rate = "1024"
> /local/domain/18/device/vbd/768/tokens-rate = "3096"
>
> > Why can't it be done with dm-ioband?
> Of cause, I/O speed limit also can be done with dm-ioband.
> But with my patch, there is no need to load dm-ioband any more.
> This patch do speed-limit more close disk, more lightweight.
I am not convienced this will be easier to maintain than
using existing code (dm-ioband) that Linux kernel provides already.
Are there other technical reasons 'dm-ioband' is not sufficient
enough? Could it be possible to fix 'dm-ioband' to not have those
bugs? Florian mentioned flush requests not passing through
the DM layers but I am pretty sure those have been fixed.
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