[Fedora-xen] slow disk performance in Xen0 FC5

Ben bench at silentmedia.com
Thu Jun 1 08:23:49 UTC 2006


It helped me a lot (but did not really fix the problem) when I set my  
disk queueing mode to deadline, from whatever it had been before. For  
instance, on my domU:
echo deadline > /sys/block/xvda/queue/scheduler

The command is similar on the dom0, just use the appropriate block  
device.

BUT, what *really* helped me out was to turn on write caching on my  
SATA raid card. It helped such an absurd amount that I have to  
suspect some corner case performance problem was being hit before,  
but I don't know what it would have been.

On May 31, 2006, at 11:07 PM, Ashe Canvar wrote:

> Hi all,
>
> My dom0 and domU machines are showing terrible disk performance  
> degradation.
>
> For instance my avg data read rate ( tested using hdparm -t /dev/hda)
> is 55MB/s using the regular smp kernel but it falls to 2.6MB/s when I
> boot into dom0. No other domains are runnign at this point. I have
> looked for incrementing interrupts in ide0 , there are none. hdparm
> shows that dma mode is enabled. dmesg shows that the same driver is
> being used for both smp and dom0 cases ( Uniform Multi-Platform E-IDE
> driver Revision: 7.00alpha2 ).
>
> I have total of 2Gig RAM in the box and dom0 is restricted to 512M.
>
> Any help appreciated !
>
> Thanks,
> -ashe
>
> [root at medusa1 ~]# rpm -qa | grep -i xen
> kernel-xenU-2.6.16-1.2080_FC5
> kernel-xen0-2.6.16-1.2080_FC5
> xen-3.0.1-4
>
> --
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> Fedora-xen at redhat.com
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