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

[Fantu <fantonifabio@xxxxxxxxxx>]

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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> 
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