0d31c7c200
The idea is that we do not need to immediately sync BAT to the image as from the guest point of view there is a possibility that IO is lost even in the physical controller until flush command was finished. bdrv_co_flush_to_os is exactly the right place for this purpose. Technically the patch uses loaded BAT data as a cache and performs actual on-disk metadata updates in parallels_co_flush_to_os callback. This patch speed ups qemu-img create -f parallels -o cluster_size=64k ./1.hds 64G qemu-io -f parallels -c "write -P 0x11 0 1024k" 1.hds writing from 50-60 Mb/sec to 80-90 Mb/sec on rotational media and from 160 Mb/sec to 190 Mb/sec on SSD disk. Signed-off-by: Denis V. Lunev <den@openvz.org> Reviewed-by: Roman Kagan <rkagan@parallels.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Roman Kagan <rkagan@parallels.com> Message-id: 1430207220-24458-25-git-send-email-den@openvz.org CC: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Read the documentation in qemu-doc.html or on http://wiki.qemu-project.org - QEMU team