Commit bdffb31d authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Jeff Cody
Browse files

mirror: do not flush every time the disks are synced 



This puts a huge strain on the disks when there are many concurrent
migrations.  With this patch we only flush twice: just before issuing
the event, and just before pivoting to the destination.  If management
will complete the job close to the BLOCK_JOB_READY event, the cost of
the second flush should be small anyway.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-id: 20161109162008.27287-2-pbonzini@redhat.com
Signed-off-by: default avatarJeff Cody <jcody@redhat.com>
parent 4e504535

block/mirror.c

+25 −15
Original line number Diff line number Diff line
@@ -615,6 +615,20 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s) 
    return 0;

}



/* Called when going out of the streaming phase to flush the bulk of the

 * data to the medium, or just before completing.

 */

static int mirror_flush(MirrorBlockJob *s)

{

    int ret = blk_flush(s->target);

    if (ret < 0) {

        if (mirror_error_action(s, false, -ret) == BLOCK_ERROR_ACTION_REPORT) {

            s->ret = ret;

        }

    }

    return ret;

}



static void coroutine_fn mirror_run(void *opaque)

{

    MirrorBlockJob *s = opaque;
@@ -727,19 +741,16 @@ static void coroutine_fn mirror_run(void *opaque) 
        should_complete = false;

        if (s->in_flight == 0 && cnt == 0) {

            trace_mirror_before_flush(s);

            ret = blk_flush(s->target);

            if (ret < 0) {

                if (mirror_error_action(s, false, -ret) ==

                    BLOCK_ERROR_ACTION_REPORT) {

                    goto immediate_exit;

            if (!s->synced) {

                if (mirror_flush(s) < 0) {

                    /* Go check s->ret.  */

                    continue;

                }

            } else {

                /* We're out of the streaming phase.  From now on, if the job

                 * is cancelled we will actually complete all pending I/O and

                 * report completion.  This way, block-job-cancel will leave

                 * the target in a consistent state.

                 */

                if (!s->synced) {

                block_job_event_ready(&s->common);

                s->synced = true;

            }
@@ -748,7 +759,6 @@ static void coroutine_fn mirror_run(void *opaque) 
                block_job_is_cancelled(&s->common);

            cnt = bdrv_get_dirty_count(s->dirty_bitmap);

        }

        }



        if (cnt == 0 && should_complete) {

            /* The dirty bitmap is not updated while operations are pending.
@@ -765,7 +775,7 @@ static void coroutine_fn mirror_run(void *opaque) 


            bdrv_drained_begin(bs);

            cnt = bdrv_get_dirty_count(s->dirty_bitmap);

            if (cnt > 0) {

            if (cnt > 0 || mirror_flush(s) < 0) {

                bdrv_drained_end(bs);

                continue;

            }