Re: [Qemu-devel] [PATCH v2] mirror: double performance of the bulk stage if the disc is full

["Denis V. Lunev" <den@openvz.org>]

On 07/14/2016 08:19 PM, Vladimir Sementsov-Ogievskiy wrote:
> Mirror can do up to 16 in-flight requests, but actually on full copy
> (the whole source disk is non-zero) in-flight is always 1. This happens
> as the request is not limited in size: the data occupies maximum available
> capacity of s->buf.
>
> The patch limits the size of the request to some artificial constant
> (1 Mb here), which is not that big or small. This effectively enables
> back parallelism in mirror code as it was designed.
>
> The result is important: the time to migrate 10 Gb disk is reduced from
> ~350 sec to 170 sec.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Fam Zheng <famz@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Max Reitz <mreitz@redhat.com>
> CC: Jeff Cody <jcody@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> ---
>
> v2: in case of s->buf_size larger than default use it to limit io_sectors
>
>   block/mirror.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/block/mirror.c b/block/mirror.c
> index b1e633e..3ac3b4d 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -23,7 +23,9 @@
>   
>   #define SLICE_TIME    100000000ULL /* ns */
>   #define MAX_IN_FLIGHT 16
> -#define DEFAULT_MIRROR_BUF_SIZE   (10 << 20)
> +#define MAX_IO_SECTORS ((1 << 20) >> BDRV_SECTOR_BITS) /* 1 Mb */
> +#define DEFAULT_MIRROR_BUF_SIZE \
> +    (MAX_IN_FLIGHT * MAX_IO_SECTORS * BDRV_SECTOR_SIZE)
>   
>   /* The mirroring buffer is a list of granularity-sized chunks.
>    * Free chunks are organized in a list.
> @@ -322,6 +324,8 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>       int nb_chunks = 1;
>       int64_t end = s->bdev_length / BDRV_SECTOR_SIZE;
>       int sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
> +    int max_io_sectors = MAX((s->buf_size >> BDRV_SECTOR_BITS) / MAX_IN_FLIGHT,
> +                             MAX_IO_SECTORS);
>   
>       sector_num = hbitmap_iter_next(&s->hbi);
>       if (sector_num < 0) {
> @@ -385,7 +389,9 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>                                             nb_chunks * sectors_per_chunk,
>                                             &io_sectors, &file);
>           if (ret < 0) {
> -            io_sectors = nb_chunks * sectors_per_chunk;
> +            io_sectors = MIN(nb_chunks * sectors_per_chunk, max_io_sectors);
> +        } else if (ret & BDRV_BLOCK_DATA) {
> +            io_sectors = MIN(io_sectors, max_io_sectors);
>           }
>   
>           io_sectors -= io_sectors % sectors_per_chunk;
guys, what about this patch?