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Re: RE: [Xen-devel] Bad read performance

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Subject: Re: RE: [Xen-devel] Bad read performance
From: Kurt Garloff <kurt@xxxxxxxxxx>
Date: Tue, 1 Mar 2005 22:15:24 +0100
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On Sat, Feb 26, 2005 at 09:04:56PM -0000, Ian Pratt wrote:
> > I notice that domain 0 gives bad performance with disk I/O. Domain 0
> > was given about 55MB RAM. With the same configuration, Linux on raw
> > hardware gives far better performance. While a raw Linux OS gives a
> > disk read throughput of around 20MB/sec (without any caching effects),
> > dom0 (using the Xen.2.0.4 kernel with linux kernel 2.6.10) gives only
> > about 2-3MB/sec throughput.
> > 
> > Any pointers to the reasons for this difference will be 
> > greatly helpful. 
> Your dom0 kernel probably does not have the proper driver for you disk
> controller compiled in...

You probably loaded ide-generic which only supports PIO.
Once loaded, you can't load the chipset specific driver (which
would support DMA) any more.

Kurt Garloff                   <kurt@xxxxxxxxxx>             [Koeln, DE]
Physics:Plasma modeling <garloff@xxxxxxxxxxxxxxxxxxx> [TU Eindhoven, NL]
Linux: SUSE Labs (Director)    <garloff@xxxxxxx>            [Novell Inc]

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