Re: [Xen-users] slow dom0 write operations with 2.6.32 pv-ops and Xen4.0.0-rc4

[benco <benco@xxxxxxx>]

Hi,

thanks for sharing, could you please post also some specs of your server and
disk system?

thanks,

roman

On Thu, Mar 04, 2010 at 06:02:24AM -0800, Fantu wrote:
> 
> on one server with xen 4 from hg unstable, kernel pv_ops xen/stable and
> performance of disk in dom0:
> dd if=/dev/zero of=/mnt/vm/disks/xpt2.disk1.xm bs=1M count=10000
> 10000+0 records in
> 10000+0 records out
> 10485760000 bytes (10 GB) copied, 146,118 s, 71,8 MB/s
> 
> 
> benco-2 wrote:
> > 
> >> You're measuring buffered (cached) performance, so when you limit
> >> the amount of cache to 2 GB the performance will be slower.
> >> 
> >> Try adding "oflag=direct" do your dd commands and test again.
> > 
> > 
> > oflag=direct option produce almost the same results on xen and non-xen
> > systems:
> > 
> > #dd if=/dev/zero of=zerofile.tst bs=1k count=1000000 oflag=direct
> > 1000000+0 records in
> > 1000000+0 records out
> > 1024000000 bytes (1.0 GB) copied, 616.219 s, 1.7 MB/s
> > 
> > what is interesting for me is the fact that with no cpu/memory limit and
> > with
> > caching the result is approx. 60% slowdown with xen kernel in comparison
> > with non-xen kernel. Is it normal?
> > 
> > thanks,
> > 
> > roman
> > 
> > 
> > <> 
> >> -- Pasi
> >> 
> >> 
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