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Re: [Xen-devel] paravirtualized vs HVM disk interference (85% vs 15%)

To: "Protti, Duilio J" <duilio.j.protti@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] paravirtualized vs HVM disk interference (85% vs 15%)
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 27 Jan 2009 08:22:05 +0000
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On 27/01/2009 05:38, "Protti, Duilio J" <duilio.j.protti@xxxxxxxxx> wrote:

> - Is the behavior ok? We mean, we consider that this interference is
> undesirable for certain deployments (anyone with paravirtualized and HVM
> guests in the same box, like in example Linux+Windows2003, and you want a fair
> share of the disk transfer rate). What we are asking is if this is a
> consequence of the Xen design and a known behavior, and if there is a
> workaround to ameliorate the interference (the problem persists and in the
> same degree even if both guests perform writes below dom0's dirty_ratio).

Run PV drivers in the HVM guest. This will automatically mean the HVM guest
is using a more efficient data channel, of the same sort as the PV guest. If
you need further fairness guarantees you can make use of one of Linux's fair
queuing disc schedulers.

 -- Keir



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