[Qemu-devel] [PULL 09/14] mirror: fix request throttling in drive-mirror

[Jeff Cody <jcody@redhat.com>]

From: "Denis V. Lunev" <den@openvz.org>

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>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 1466598927-5990-1-git-send-email-den@openvz.org
CC: Jeff Cody <jcody@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
(cherry picked from commit e648dc95c28fbca12e67be26a1fc4b9a0676c3fe)
---
 block/mirror.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/mirror.c b/block/mirror.c
index f78186d..836a5d0 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -407,6 +407,11 @@ 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:
@@ -695,7 +700,7 @@ static void coroutine_fn mirror_run(void *opaque)
         delta = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - s->last_pause_ns;
         if (delta < 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);
-- 
1.9.3