[PATCH 0/9] kvm tools, qcow: Improve QCOW performance

Pekka Enberg
2011-07-09T13:03:01Z

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

For comparison, the results for raw ext4 images are as follows:

[ seekwatcher: http://userweb.kernel.org/~penberg/kvm-qcow-delayed/kvm-raw.png ]

511229952 bytes (511 MB) copied, 8.75403 s, 58.4 MB/s
511229952 bytes (511 MB) copied, 10.3326 s, 49.5 MB/s
511229952 bytes (511 MB) copied, 6.8494 s, 74.6 MB/s
511229952 bytes (511 MB) copied, 9.21538 s, 55.5 MB/s
511229952 bytes (511 MB) copied, 8.52883 s, 59.9 MB/s
511229952 bytes (511 MB) copied, 8.13298 s, 62.9 MB/s
511229952 bytes (511 MB) copied, 5.03801 s, 101 MB/s

Pekka

Pekka Enberg (9):
kvm tools, qcow: Rename struct qcow_l2_cache to struct qcow_l2_table
kvm tools, qcow: Use 'struct qcow_l2_table' instead of untyped array
kvm tools, qcow: Fix locking issues
kvm tools, qcow: Introduce qcow_disk_flush()
kvm tools, qcow: Delayed L1 table writeout
kvm tools, qcow: Don't fdatasync() L2 table writeout
kvm tools, qcow: Use big endian order for L2 table entries
kvm tools, qcow: Delayed L2 table writeout
kvm tools, qcow: Flush only dirty L2 tables

tools/kvm/disk/qcow.c | 248 ++++++++++++++++++++++-------------------
tools/kvm/include/kvm/mutex.h | 6 +
tools/kvm/include/kvm/qcow.h | 6 +-
3 files changed, 145 insertions(+), 115 deletions(-)