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. Pekka -- 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
