Re: [libvirt-users] Yet another disk I/O performance issue

Pierre Schweitzer
2014-01-20T14:20:13Z

Hey,

First of all, you don't need to set scheduler as deadline on VM. Just
disable it (elevator=none). The HV will handle it for the VM.

Furthermore, as generic performance optimization, I recommend you
disable swappiness on the HV, as well as zone reclaim.

I invite you to read this IBM paper:
http://pic.dhe.ibm.com/infocenter/lnxinfo/v3r0m0/index.jsp?topic=/liaat/liaattunkickoff.htm
It's quite a good starting point.

Regards,

On 01/19/2014 08:01 PM, Matteo Lanati wrote:
> Hi all,
>
> I'm running a VM using libvirt+KVM and I have a disk performance issue.
>
> The host is the following:
> 4 cores Intel Xeon 5140@2.33 GHz, 16 GB of RAM, SATA HDD, OS Debian Wheezy,
> libvirt 0.9.12-11, QEMU-KVM 1.1.2+dfsg-2.
>
> The guest:
> 1 CPU, 2 GB RAM running Debian 7.0, image in compressed qcow2 format.
>
> When I try do run "dd if=/dev/zero of=io.test bs=32768k count=40"
I get
> around 500 MB/s on bare metal, while only around 30 MB/s inside the VM.
>
> I'm trying to get something more out of the virtualization layer, I
hope
> that there's room for improvement.
>
> I'm using virtio, I aready set cache='none' and
io='native' in the domain
> definition. Both host and guest are using deadline as I/O scheduler. The VM
> uses an ext4 filesystem, while the image is saved on an ext3 disk. I
> mounted the host and guest filesystems specifying nodiratime and noatime
> options. Even if I convert the image to raw format nothing changes.
> I didn't mess with iotune nor blockio.
>
> Is there something that I overlooked or any other suggestion?
>
> Thanks in advance for your help.
>
> Matteo
>
>
>
>
>
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> libvirt-users@redhat.com
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--
Pierre Schweitzer <pierre@reactos.org>
System Administrator
ReactOS Foundation