* Pekka Enberg <penberg@xxxxxxxxxx> wrote: > Hi Ingo, > > * Pekka Enberg <penberg@xxxxxxxxxx> wrote: > >> This series fixes QCOW locking issues and implements delayed metadata writeout. > >> This improves performance of writeout to QCOW2 images that don't have clusters > >> and L2 tables allocated on-disk. > >> > >> I tested the series by running > >> > >> mount -t ext4 /dev/vdb /mnt > >> dd if=/dev/zero of=/mnt/tmp > >> > >> in the guest multiple times for fresly generated QCOW2 image: > >> > >> dd if=/dev/zero of=fs.ext4 bs=1024k count=512 && mkfs.ext4 -F fs.ext4 && qemu-img convert -O qcow2 fs.ext4 fs.qcow2 > >> > >> which causes worst-case behavior for the current code. > >> > >> Before: > >> > >> [ seekwatcher: http://userweb.kernel.org/~penberg/kvm-qcow-delayed/kvm-qcow2-master.png ] > >> > >> 511229952 bytes (511 MB) copied, 19.906 s, 25.7 MB/s > >> 511229952 bytes (511 MB) copied, 20.3168 s, 25.2 MB/s > >> 511229952 bytes (511 MB) copied, 20.8078 s, 24.6 MB/s > >> 511229952 bytes (511 MB) copied, 21.0889 s, 24.2 MB/s > >> 511229952 bytes (511 MB) copied, 20.7833 s, 24.6 MB/s > >> 511229952 bytes (511 MB) copied, 20.7536 s, 24.6 MB/s > >> 511229952 bytes (511 MB) copied, 20.0312 s, 25.5 MB/s > >> > >> After: > >> > >> [ seekwatcher: http://userweb.kernel.org/~penberg/kvm-qcow-delayed/kvm-qcow2-delayed.png ] > >> > >> 511229952 bytes (511 MB) copied, 7.68312 s, 66.5 MB/s > >> 511229952 bytes (511 MB) copied, 7.54065 s, 67.8 MB/s > >> 511229952 bytes (511 MB) copied, 9.34749 s, 54.7 MB/s > >> 511229952 bytes (511 MB) copied, 9.2421 s, 55.3 MB/s > >> 511229952 bytes (511 MB) copied, 9.9364 s, 51.5 MB/s > >> 511229952 bytes (511 MB) copied, 10.0337 s, 51.0 MB/s > >> 511229952 bytes (511 MB) copied, 9.39502 s, 54.4 MB/s > > On Sun, Jul 10, 2011 at 8:15 PM, Ingo Molnar <mingo@xxxxxxx> wrote: > > Just wondering, how does Qemu perform on the same system using the > > same image, with comparable settings? > > Freshly built from qemu-kvm.git: > > $ /home/penberg/qemu-kvm/x86_64-softmmu/qemu-system-x86_64 --version > QEMU emulator version 0.14.50 (qemu-kvm-devel), Copyright (c) > 2003-2008 Fabrice Bellard > > Tests were run with this configuration: > > $ /home/penberg/qemu-kvm/x86_64-softmmu/qemu-system-x86_64 -kernel > /boot/vmlinuz-3.0.0-rc5+ -drive > file=/home/penberg/images/debian_squeeze_amd64_standard.img,if=virtio,boot=on > -drive file=fs.qcow2,if=virtio -nographic -m 320 -smp 2 -append > "root=/dev/vda1 console=ttyS0 init=/root/iobench-write" > > Not sure if that's 100% comparable settings but anyway. The results > looks as follows: > > 511229952 bytes (511 MB) copied, 12.5543 s, 40.7 MB/s > 511229952 bytes (511 MB) copied, 9.50382 s, 53.8 MB/s > 511229952 bytes (511 MB) copied, 12.1092 s, 42.2 MB/s > 511229952 bytes (511 MB) copied, 13.2981 s, 38.4 MB/s > 511229952 bytes (511 MB) copied, 11.3314 s, 45.1 MB/s > 511229952 bytes (511 MB) copied, 12.7505 s, 40.1 MB/s > 511229952 bytes (511 MB) copied, 11.2921 s, 45.3 MB/s > > This is what I'd expect as tools/kvm has much more relaxed sync() > guarantees than qemu-kvm. We treat all writes to QCOW2 images as > volatile until VIRTIO_BLK_T_FLUSH is issued. Furthemore, for this > particular (special case) load, it's pretty much append-only to the > backing file which is why QCOW is so close to raw image performance > here. Pretty impressive numbers! To relax Qemu's caching guarantees you can append ,cache=writeback to your -drive option, i.e. something like: -drive file=/dev/shm/test.qcow2,cache=writeback,if=virtio Does that improve the Qemu results? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
