Re: slow guest performance with build load, looking for ideas

[Avi Kivity <avi@redhat.com>]

On 07/09/2009 05:36 AM, Erik Jacobson wrote:
>> Haven't followed the thread in great detail, but has anyone tried
>> putting the virtio disk back into rotational mode?
>>      
>
> Hello.  I haven't had a chance to try all the suggestions in the thread
> so far.  However, I did just run some tests with block queue rotation
> settings tonight.
>
> For the problem where mkfs.ext3 on a virtio disk image (raw image, not
> pre-allocated) the timing went from like 27 minutes for a 10gb fs down
> to just over 2 minutes.  So that was a huge difference.
>
> For the linux kernel build test, there was a difference, but less dramatic.
> I'd say the performance is still below what I expected.  I haven't given
> up yet, there is more to try in the thread.  I just wanted to post these
> results.
>
> The HW in use is the same as in the rest of the tread, including the
> virtio disk type.  Since my last post, fedora 11 updates have been
> applied to the system.
>
> Timing with the rotational stuff set to 1...
>
> real    14m13.015s
> user    29m42.162s
> sys     8m37.416s
>    

(user + sys) / real = 2.7

> And finally, to confirm the numbers on the host with no guest running...
> The same disk/filesystem, now mounted on the host instead of the guest, gave
> this timing:
>
> real    6m13.398s
> user    26m56.061s
> sys     5m34.477s
>    

(user + sys) / real = 5.2

I got 6.something in a guest!

> For the guest runs, qemu command was as follows.  For later tests, I will
> combine the queue rotation setting with the other suggestions.
>
> /usr/bin/qemu-kvm -M pc -m 4096 -smp 8 -name f11-test -uuid b7b4b7e4-9c07-22aa-0c95-d5c8a24176c5 -monitor pty -pidfile /var/run/libvirt/qemu//f11-test.pid -drive file=/var/lib/libvirt/images/f11-test.img,if=virtio,index=0,boot=on -drive file=/dev/sdb,if=virtio,index=1 -drive file=/var/lib/libvirt/images/test.img,if=virtio,index=2 -net nic,macaddr=54:52:00:46:48:0e,model=virtio -net user -serial pty -parallel none -usb -usbdevice tablet -vnc cct201:1 -soundhw es1370 -redir tcp:5555::22
>    

Please drop -usbdevice tablet and set the host I/O scheduler to 
deadline.  Add cache=none to the -drive options.

-- 
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