Re: virtio-blk performance regression and qemu-kvm

[Martin Mailand <martin@tuxadero.com>]

Am 06.03.2012 13:59, schrieb Stefan Hajnoczi:
> Yes, the reason why that would be interesting is because it allows us
> to put the performance gain with master+"performance" into
> perspective.  We could see how much of a change we get.
>
> Does the CPU governor also affect the result when you benchmark with
> real disks instead of ramdisk?  I can see how the governor would
> affect ramdisk, but would expect real disk I/O to be impacted much
> less.


Hi,
here my results.
I tested with "fio -name iops -rw=read -size=1G -iodepth 1 -filename 
/dev/vdb -ioengine libaio -direct 1 -bs 4k"

The qemu command was.

qemu-system-x86_64 --enable-kvm -m 512 -boot c \
-drive file=/home/martin/vmware/bisect_kvm/hda.img,cache=none,if=virtio 
-drive file=/dev/ram0,cache=none,if=virtio
-drive file=/dev/sda2,cache=none,if=virtio

Host Kernel 3.3.0+rc4
Guest Kernel 3.0.0-16-generic ubuntu kernel

On the host I use a raw partition sda2 for the disk test, in qemu I 
write with fio to /dev/vdc, though there is no fs involved.
The host disk can at max. 13K iops, in qemu I get at max 6,5K iops, 
that's around about 50% overhead. All the test were with 4k reads, so I 
think we are mostly latency bound.

-martin

log:

** v0.14.1 ondemand **

ram
bw=61038KB/s iops=15259
bw=66190KB/s iops=16547

disk
bw=18105KB/s iops=4526
bw=17625KB/s iops=4406

** v0.14.1 performance **

ram
bw=72356KB/s iops=18088
bw=72390KB/s iops=18097

disk
bw=27886KB/s iops=6971
bw=27915KB/s iops=6978


** master ondemand  **

ram
bw=24833KB/s iops=6208
bw=27275KB/s iops=6818

disk
bw=14980KB/s iops=3745
bw=14881KB/s iops=3720

** master performance **

ram
bw=64318KB/s iops=16079
bw=63523KB/s iops=15880

disk
bw=27043KB/s iops=6760
bw=27211KB/s iops=6802


Host Disk Test (SanDisk SSD U100)

host disk ondemand
bw=48823KB/s iops=12205
bw=49086KB/s iops=12271

host disk performance
bw=55156KB/s iops=13789
bw=54980KB/s iops=13744