Re: [Qemu-devel] [PATCH] rbd : disable rbd_cache_writethrough_until_flush for cache=unsafe

[Josh Durgin]

On 07/27/2016 05:26 AM, Alexandre Derumier wrote:
> ceph force writethrough until a flush is detected.
> With cache=unsafe, we never send flush.
> So we need to tell to ceph
> to set rbd_cache_writethrough_until_flush=false in this case.
>
> This speedup a lot qemu-img convert which use cache=unsafe by default
>
> Signed-off-by: Alexandre Derumier <address@hidden>

Sorry for the delay - this is correct and needed since this option
appeared by default in Ceph hammer.

Reviewed-by: Josh Durgin <address@hidden>

> ---
>  block/rbd.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 0106fea..f3af6c8 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -552,6 +552,10 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict 
> *options, int flags,
>          rados_conf_set(s->cluster, "rbd_cache", "true");
>      }
>
> +    if (flags & BDRV_O_NO_FLUSH) {
> +        rados_conf_set(s->cluster, "rbd_cache_writethrough_until_flush", 
> "false");
> +    }
> +
>      r = rados_connect(s->cluster);
>      if (r < 0) {
>          error_setg_errno(errp, -r, "error connecting");