Re: [Qemu-devel] [PATCH 1/1] mirror: fix request throttling in drive-mirror

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

On 06/22/2016 03:35 PM, Denis V. Lunev wrote:
> There are 2 deficiencies here:
> - mirror_iteration could start several requests inside. Thus we could
>    simply have more in_flight requests than MAX_IN_FLIGHT.
> - keeping this in mind throttling in mirror_run which is checking
>    s->in_flight == MAX_IN_FLIGHT is wrong.
>
> The patch adds the check and throttling into mirror_iteration and fixes
> the check in mirror_run() to be sure.
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Jeff Cody <jcody@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Max Reitz <mreitz@redhat.com>
> ---
>   block/mirror.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/block/mirror.c b/block/mirror.c
> index a04ed9c..e881ef6 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -399,6 +399,11 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>               }
>           }
>   
> +        while (s->in_flight >= MAX_IN_FLIGHT) {
> +            trace_mirror_yield_in_flight(s, sector_num, s->in_flight);
> +            mirror_wait_for_io(s);
> +        }
> +
>           mirror_clip_sectors(s, sector_num, &io_sectors);
>           switch (mirror_method) {
>           case MIRROR_METHOD_COPY:
> @@ -634,7 +639,7 @@ static void coroutine_fn mirror_run(void *opaque)
>            */
>           if (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - last_pause_ns < SLICE_TIME &&
>               s->common.iostatus == BLOCK_DEVICE_IO_STATUS_OK) {
> -            if (s->in_flight == MAX_IN_FLIGHT || s->buf_free_count == 0 ||
> +            if (s->in_flight >= MAX_IN_FLIGHT || s->buf_free_count == 0 ||
>                   (cnt == 0 && s->in_flight > 0)) {
>                   trace_mirror_yield(s, s->in_flight, s->buf_free_count, cnt);
>                   mirror_wait_for_io(s);
ping