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

[Jeff Cody <jcody@redhat.com>]

On Wed, Jun 22, 2016 at 03:35:27PM +0300, 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);
> -- 
> 2.1.4
>

Reviewed-by: Jeff Cody <jcody@redhat.com>