commit 4b5004d9fc5b7d8e4447dc81c2f26477c2d590f7
author Denis V. Lunev <den@openvz.org> Thu Jul 14 16:33:29 2016 +0300
committer Jeff Cody <jcody@redhat.com> Tue Jul 19 17:02:49 2016 -0400
tree 6186bb4e9cdaec5f85a732f135368c15ddcaf6b3
parent c7c2769c0e5769eaad9d968fe2161505b657e02a

mirror: improve performance of mirroring of empty disk

We should not take into account zero blocks for delay calculations.
They are not read and thus IO throttling is not required. In the
other case VM migration with 16 Tb QCOW2 disk with 4 Gb of data takes
days.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 1468503209-19498-9-git-send-email-den@openvz.org
CC: Stefan Hajnoczi <stefanha@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>
Signed-off-by: Jeff Cody <jcody@redhat.com>

block/mirror.c

diff --git a/block/mirror.c b/block/mirror.c
index 0262b03..f78186d 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -323,6 +323,7 @@
     int nb_chunks = 1;
     int64_t end = s->bdev_length / BDRV_SECTOR_SIZE;
     int sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
+    bool write_zeroes_ok = bdrv_can_write_zeroes_with_unmap(blk_bs(s->target));
 
     sector_num = hbitmap_iter_next(&s->hbi);
     if (sector_num < 0) {
@@ -373,7 +374,7 @@
     bitmap_set(s->in_flight_bitmap, sector_num / sectors_per_chunk, nb_chunks);
     while (nb_chunks > 0 && sector_num < end) {
         int ret;
-        int io_sectors;
+        int io_sectors, io_sectors_acct;
         BlockDriverState *file;
         enum MirrorMethod {
             MIRROR_METHOD_COPY,
@@ -410,12 +411,17 @@
         switch (mirror_method) {
         case MIRROR_METHOD_COPY:
             io_sectors = mirror_do_read(s, sector_num, io_sectors);
+            io_sectors_acct = io_sectors;
             break;
         case MIRROR_METHOD_ZERO:
-            mirror_do_zero_or_discard(s, sector_num, io_sectors, false);
-            break;
         case MIRROR_METHOD_DISCARD:
-            mirror_do_zero_or_discard(s, sector_num, io_sectors, true);
+            mirror_do_zero_or_discard(s, sector_num, io_sectors,
+                                      mirror_method == MIRROR_METHOD_DISCARD);
+            if (write_zeroes_ok) {
+                io_sectors_acct = 0;
+            } else {
+                io_sectors_acct = io_sectors;
+            }
             break;
         default:
             abort();
@@ -424,7 +430,7 @@
         sector_num += io_sectors;
         nb_chunks -= DIV_ROUND_UP(io_sectors, sectors_per_chunk);
         if (s->common.speed) {
-            delay_ns = ratelimit_calculate_delay(&s->limit, io_sectors);
+            delay_ns = ratelimit_calculate_delay(&s->limit, io_sectors_acct);
         }
     }
     return delay_ns;