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

From: Erik Jacobson <erikj@sgi.com>
To: Mark McLoughlin <markmc@redhat.com>
Cc: Avi Kivity <avi@redhat.com>, Erik Jacobson <erikj@sgi.com>,
	kvm@vger.kernel.org
Subject: Re: slow guest performance with build load, looking for ideas
Date: Wed, 8 Jul 2009 21:36:33 -0500	[thread overview]
Message-ID: <20090709023633.GB29409@sgi.com> (raw)
In-Reply-To: <1246635797.13604.7.camel@blaa>

> 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

To confirm this was really better, I halted the virtual machine and restarted
it without doing setting the rotational values to 1.  I got this timing:

real    16m50.829s
user    29m33.933s
sys     9m4.905s

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

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