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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
