Re: [Qemu-devel] [PATCH 21/27] block/parallels: no need to flush on each block allocation table update

[Roman Kagan]

On Tue, Mar 10, 2015 at 11:51:15AM +0300, Denis V. Lunev wrote:
> From the point of guest each write to real disk prior to disk barrier
> operation could be lost. Therefore there is no problem that "not synced"
> new block is lost due to not updated allocation table if QEMU is crashed.
> This situation is properly detected and handled now using inuse magic
> and in parallels_check
> 
> This patch improves writing performance of
>   qemu-img create -f parallels -o cluster_size=64k ./1.hds 64G
>   qemu-io -f parallels -c "write -P 0x11 0 1024k" 1.hds
> from 45 Mb/sec to 160 Mb/sec on my SSD disk. The gain on rotational media
> is much more sufficient, from 800 Kb/sec to 45 Mb/sec.
> 
> 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 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Roman Kagan <address@hidden>

Roman.