Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm

[Ross Becker <ross.becker@gmail.com>]

I just joined in order to chime in here-

I'm seeing the exact same thing as Reeted;  I've got a machine with a
storage subsystem capable of 400k IOPs, and when I punch the storage up to
VMs, each VM seems to top out at around 15-20k IOPs.   I've managed to get
to 115k IOPs by creating 8 VMs, doing appropriate CPU pinning to spread
them amongst physical cores, and running IO in them simultaneously, but
I'm unable to get a single VM past 20k IOPs.

I'm using kvm-qemu 12.1.2, as distributed in RHEL 6.2.

The hardware is a Dell R910 chassis, with 4 intel E7 processors.  I am
poking LVM logical volume block devices directly up to VMs as disks,
format raw, virtio driver, write caching none, IO mode native.  Each VM
has 4 vCPUs.

I'm also using fio to do my testing.

The interesting thing is that throughput is actually pretty fantastic; I'm
able to push 6.3 GB/sec using 256k blocks, but the IOPs @ 4k block size
are poor.

I am happy to provide any config details, or try any tests suggested.


--Ross