Re: libvirt qemu/kvm/rbd inside VM read slow

[Steffen Thorhauer <steffen.thorhauer@xxxxxxxxxxxxxxxxxxxxxxx>]

On 01/10/2014 02:35 PM, Wido den Hollander wrote:

Op 10 jan. 2014 om 18:49 heeft "Steffen Thorhauer" <steffen.thorhauer@xxxxxxxxxxxxxxxxxxxxxxx> het volgende geschreven:

On 01/10/2014 01:21 PM, Ирек Фасихов wrote:

You need to use VirtIO.

   <target dev='vdb' bus='virtio'/>

with this parameter ist not a real performance increase:
 dd if=/dev/zero of=zerofile-2 bs=1G count=8
8+0 records in
8+0 records out
8589934592 bytes (8.6 GB) copied, 73.8425 s, 116 MB/s

and reading:

trompete@multius:~$ dd if=zerofile-2 of=/dev/null bs=1G count=8
8+0 records in
8+0 records out
8589934592 bytes (8.6 GB) copied, 429.528 s, 20.0 MB/s

What happens if you increase the read_ahead_kb value for the device to 4096k. That is inside the guest.

cat read_ahead_kb
65536

trompete@multius:~$ dd if=zerofile-2 of=/dev/null bs=1G count=8
8+0 records in
8+0 records out
8589934592 bytes (8.6 GB) copied, 382.148 s, 22.5 MB/s

-- 
______________________________________________________________________
Steffen Thorhauer

Department of Technichal and Business Information Systems (ITI)
Faculty of Computer Science (FIN)
  Otto von Guericke University Magdeburg
Universitaetsplatz 2
39106 Magdeburg, Germany

phone: 0391 67 52996
fax: 0391 67 12341
email: sth@xxxxxxxxxxxxxxxxxxxxxxx
url: http://wwwiti.cs.uni-magdeburg.de/~thorhaue        

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