On Sat, Jul 24, 2021 at 04:38:46PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> There is no conflict and no dependency if we have parallel writes to
> different subclusters of one cluster when cluster itself is already
when the cluster itself
> allocated. So, relax extra dependency.
>
> Measure performance:
> First, prepare build/qemu-img-old and build/qemu-img-new images.
>
> cd scripts/simplebench
> ./img_bench_templater.py
>
> Paste the following to stdin of running script:
>
> qemu_img=../../build/qemu-img-{old|new}
> $qemu_img create -f qcow2 -o extended_l2=on /ssd/x.qcow2 1G
> $qemu_img bench -c 100000 -d 8 [-s 2K|-s 2K -o 512|-s $((1024*2+512))] \
> -w -t none -n /ssd/x.qcow2
>
> The result:
>
> All results are in seconds
>
> ------------------ --------- ---------
> old new
> -s 2K 6.7 ± 15% 6.2 ± 12%
> -7%
> -s 2K -o 512 13 ± 3% 11 ± 5%
> -16%
> -s $((1024*2+512)) 9.5 ± 4% 8.4
> -12%
> ------------------ --------- ---------
Cool improvement.
>
> So small writes are more independent now and that helps to keep deeper
> io queue which improves performance.
>
> 271 iotest output becomes racy for three allocation in one cluster.
> Second and third writes may finish in different order. Second and
> third requests don't depend on each other any more. Still they both
> depend on first request anyway. Keep only one for consistent output.
Interesting fallout. Yes, it looks like the test is still robust
enough without the extra request.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
> ---
> block/qcow2-cluster.c | 11 +++++++++++
> tests/qemu-iotests/271 | 4 +---
> tests/qemu-iotests/271.out | 2 --
> 3 files changed, 12 insertions(+), 5 deletions(-)
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
