Before commit 580b6b2aa2(dataplane: use the Qemu block
layer for I/O), dataplane for virtio-blk submits block
I/O at batch.
This commit 580b6b2aa2 replaces the custom linux AIO
implementation(including I/O batch) with Qemu block
layer, but this commit causes ~40% throughput regression
on virtio-blk performance, and removing submitting I/O
at batch is one of the cause.
This patch applys the new introduced bdrv_io_plug() and
bdrv_io_unplug() interfaces to support submitting I/O
at batch for Qemu block layer, and in my test, the change
can improve thoughput by ~30% with 'aio=native'.
Following my fio test script:
[global]
direct=1
size=4G
bsrange=4k-4k
timeout=40
numjobs=4
ioengine=libaio
iodepth=64
filename=/dev/vdc
group_reporting=1
[f]
rw=randread
Result on one of my small machine(host: x86_64, 2cores, 4thread, guest: 4cores):
- qemu master: 62K IOPS
- qemu master with these patches: 84K IOPS
- 2.0.0 release(dataplane using custom linux aio): 97K IOPS
Signed-off-by: Ming Lei <ming....@canonical.com>
---
hw/block/dataplane/virtio-blk.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index c10b7b7..5deaddc 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -289,6 +289,7 @@ static void handle_notify(EventNotifier *e)
int ret;
event_notifier_test_and_clear(&s->host_notifier);
+ bdrv_io_plug(s->blk->conf.bs);
for (;;) {
/* Disable guest->host notifies to avoid unnecessary vmexits */
vring_disable_notification(s->vdev, &s->vring);
@@ -322,6 +323,7 @@ static void handle_notify(EventNotifier *e)
break;
}
}
+ bdrv_io_unplug(s->blk->conf.bs);
}
/* Context: QEMU global mutex held */
@@ -431,6 +433,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
trace_virtio_blk_data_plane_start(s);
bdrv_set_aio_context(s->blk->conf.bs, s->ctx);
+ bdrv_init_io_queue(s->blk->conf.bs, 128);
/* Kick right away to begin processing requests already in vring */
event_notifier_set(virtio_queue_get_host_notifier(vq));
@@ -462,6 +465,8 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
aio_context_release(s->ctx);
+ bdrv_exit_io_queue(s->blk->conf.bs);
+
/* Sync vring state back to virtqueue so that non-dataplane request
* processing can continue when we disable the host notifier below.
*/
--
1.7.9.5
