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RE: [Xen-users] Poor hard disk performance on xen-3/dom0

To: "Woon Wai Keen @ doubleukay.com" <doubleukay@xxxxxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] Poor hard disk performance on xen-3/dom0
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 30 Dec 2005 18:46:05 -0000
Cc: ian.pratt@xxxxxxxxxxxx
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Thread-topic: [Xen-users] Poor hard disk performance on xen-3/dom0
Compare the boot messages of vanilla vs. xen -- you're likely using a
different driver.

I know everyone always ignores me whenever I say this, but users really
should be using the -xen kernel rather than -xen0/U. The latter two are
just to make build times quicker for developers. The -xen kernel has way
more drivers, though built as modules, so you'll need to make an initrd.


> On a vanilla 2.6.12 kernel, I get:
>    60MB/s for hdparm -t /dev/sd[a|b] (on an Intel ICH7 SATA 
> controller).
>    30MB/s for hdparm -t /dev/hda (Intel ICH7)
> While on the xen dom0 kernel, I get 20MB/s for all three 
> devices. I confirm that DMA is enabled for the PATA hard 
> disk. I don't know how to check that for the SATA hard disks, 
> but I assume that they're on DMA mode too.
> Xen is compiled with the following:
> xen_changeset          : Fri Dec  9 11:05:06 2005 +0000 
> 8311:53cff3f88e45
> cc_compiler            : gcc version 3.3.5 (Debian 1:3.3.5-13)
> The dom0 kernel is compiled with almost the same options as 
> the vanilla kernel, barring the xen-exclusive and 
> nonxen-exclusive options.
> Does anyone else face similar problems?
> --
> Regards,
> wK (www.doubleukay.com)

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