Re: [Xen-users] Disk starvation between DomU's

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-06-10 at 08:24 +0000, Thanos Makatos wrote:
> 
> > -----Original Message-----
> > From: xen-users-bounces@xxxxxxxxxxxxx [mailto:xen-users-
> > bounces@xxxxxxxxxxxxx] On Behalf Of Wiebe Cazemier
> > Sent: 10 June 2013 09:11
> > To: xen-users@xxxxxxxxxxxxx
> > Subject: [Xen-users] Disk starvation between DomU's
> > 
> > Hi,
> > 
> > I have the issue of my virtual machines becoming extremely slow when
> > even only one of them is creating a lot of I/O. Is there a way to
> > prioritize disk access? I can't seem to find any.
> > 
> > The Xen host in question is:
> > 
> > - Quad core Xeon X3430  @ 2.40GHz
> > - 3Ware 9650SE RAID6 array, Seagate 2 TB disks.
> > - Xen 4.0.1-5.8 on Debian 6 (upgrade planned)
> > - 15 DomU's
> > - All VM's have noop as disk scheduler (cat
> > /sys/block/xvda2/queue/scheduler)
> > - VM's are prioritized with 'xm sched-cred', but that doesn't help the
> > disk much.
> > - Dom-0 has significantly more credits (10000) because it needs to
> > service IO's.
> > - Dom-0 doesn't do anything else.
> > - All virtual disks are logical volumes, exposed to the VM through xen-
> > blkfront
> > 
> > So, what can I do to improve disk performance or priority?
> 
> Can you try using ionice to set the disk priority of the corresponding 
> tapdisk/qemu process?

....Or if using blkback the relevant kernel thread.

Ian.



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