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Re: [Xen-users] Difference performances between HVM and PV guest in hard

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Subject: Re: [Xen-users] Difference performances between HVM and PV guest in hard disc reading
From: Javier Guerra <javier@xxxxxxxxxxx>
Date: Sat, 30 May 2009 20:02:46 -0500
Cc: Heli <helicoterus-elih@xxxxxxxx>, "Fajar A. Nugraha" <fajar@xxxxxxxxx>
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Heli wrote:
> How is it possible that a PV domU returns 180 MB/sec if on a normal 
> linux hdparm returns 45 MB/sec?

easy, if the 'block device' is in fact a file on Dom0, with a lot more RAM 
available for cache

but as soon as you do real load, that cache becomes a nuisianse.  you get much 
better performance if you turn the cache off (with tap:) or use a block device 
(with phy:), even if the benchmarks drop down to realistic levels


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