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Re: [Xen-users] Re: I/O performance.

To: "Sven Köhler" <skoehler@xxxxxx>
Subject: Re: [Xen-users] Re: I/O performance.
From: "Tim Wood" <twwood@xxxxxxxxx>
Date: Mon, 28 Aug 2006 15:17:05 -0400
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One thing I've noticed is that if you have 2 VMs on a server and one
is running a IO intensive task while the other is CPU intensive, the
IO task tends to get starved and performs very poorly.  This seems
like a scheduling problem, so perhaps the new credit scheduler helps
with this, although I haven't tried.

So to further complicate how to measure I/O performance there is the
issue of interference with other VMs.


On 8/28/06, Sven Köhler <skoehler@xxxxxx> wrote:
> What performance penalty I should expect from the I/O under domU ?
>
> Does it matter to the I/O if the CPU has hardware virtualization ?

Me, personally, would be interested in the performance in the case that
the DomU accesses a block device on the host though the "most optimized"
case - namely if the DomU is using the Xen frontend and the Xen backend
of the Dom0 to access the device.

There are many questions, like:
Does Xen allow the DomU to make multiple requests that are then queued
on the Dom0 or even passed to the lower level SCSI/SATA driver of the
Dom0? And so on ...



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