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

[Jan Kundrát <jan.kundrat@xxxxxx>]

Anthony Liguori wrote:
> On Sat, 2005-01-15 at 08:36, Jan Kundrát wrote:
>
> > Anthony Liguori wrote:
> > yes, dom0 filesystems are on partitions located on hda.
>
> My theory is that since hda is a single disk if you've got dom0 reading
> and writing to it and another partition reading and writing to the same
> disk at the same time both are going to be slower than if you were just
> writing to hda on dom0.
OK, I'll try to add another device and play with it. BTW, both dom0 and 
the domain<n> (running ttylinux) was idle, almost without disk activity. 
I just run `hdparm` inside dom0, waited for results, dtto in domainU, 
and repeated several times.
> That's why I suggest trying it with a neutral device.
>
>
> > I've tried exporting /dev/hda7 (not used neither mounted from dom0) as 
> > sdb7 and I can get about 12.3 MB/s. From dom0 I get about 14.8 MB/s.
>
> That seems pretty reasonable.  Doesn't seem like there's a problem. 
> Sharing partitions between dom0 and domU seems like a bad idea.  Look
> through the threads in the list about filesystem corruption.
30% performance loss seems like a problem for me ;-), comparing to <3% 
(iirc) in xen's benchmarks. I just want to find out if the problem is in 
Xen.
Of course I'm *not* sharing the same partition between domains, I'm only 
performing read benchmarks on the same disk location.
-jkt

--
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