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Re: [Xen-users] CPU intensive VM starves IO intensive VMs

To: "Diwaker Gupta" <diwaker.lists@xxxxxxxxx>
Subject: Re: [Xen-users] CPU intensive VM starves IO intensive VMs
From: "Tim Wood" <twwood@xxxxxxxxx>
Date: Sun, 3 Sep 2006 12:09:44 -0400
Cc: "Apparao, Padmashree K" <padmashree.k.apparao@xxxxxxxxx>, Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>
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Thanks for your replies.

Agreed that wasn't the best hog program, I'll take a look into slurp.

This was all using the work conserving scheduler.  I imagine using
non-work conserving would help in this particular case, but seems self
defeating if the goal is trying to raise overall performance.

I'm sure multiple cpus would change things, however I think it is
significant that single cpu Xen has such bad IO performance when
either a) running a cpu bound process in Dom0 or a 2nd VM or b)
running both a cpu bound and IO bound process in one VM.

There are two possible explanations - either the scheduler does a poor
job of allocating Dom0 and the IO VM when they need it, or the cpu
overhead of doing IO in Xen is very high.  I notice that when I have
an IO bound VM, 100% of the cpu is being used according to XenMon
(most in dom0 and some in that VM) while in reality there should be
plenty of spare cycles.

I'm getting kernel panics in xen-unstable, so I am putting off testing
the new scheduler for a bit...

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