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Re: [Xen-devel] poor I/O performance on domU

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] poor I/O performance on domU
From: Jan Kundrát <jan.kundrat@xxxxxx>
Date: Thu, 13 Jan 2005 18:08:18 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
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Anthony Liguori wrote:
I think that's a reasonable answer. It should be easy to test though. Try your same test on dom0 and use /dev/loopN where N is the loopback
device that has your rootfs on it.


Only rootfs is exported from loopback device and I'm benchmarking access to dom0's /dev/hda exported to domU as read-only.

As the rootfs image is quite small (16MB), I can't easily test access speeds because it will fit into cache.

The difference between testing /dev/loopN access on dom0 and the virtual
block device on domU should tell you the Xen-imposed performance
penalty.

I did a quick test on my system and there was a 50% slowdown using the
loopback device doing your test so I imagine it's that.

Accessing exported loopback or some other device?


-jkt

--
cd /local/pub && more beer > /dev/mouth



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