Re: [Qemu-devel] [PATCH 24/27] block/parallels: delay writing to BAT till bdrv_co_flush_to_os

[Roman Kagan]

On Tue, Mar 10, 2015 at 11:51:18AM +0300, Denis V. Lunev wrote:
> 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 <address@hidden>
> CC: Roman Kagan <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> ---
>  block/parallels.c | 50 ++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 44 insertions(+), 6 deletions(-)

Reviewed-by: Roman Kagan <address@hidden>

Roman.