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/liaa... 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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