diff options
| author | Ming Lei <ming.lei@canonical.com> | 2014-05-30 10:49:29 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2014-05-30 08:19:39 -0600 |
| commit | e8edca6f7f92234202d6dd163c118ef495244d7c (patch) | |
| tree | 3546ab7cd1062b0cad3007818c08e468aa189a0c /drivers/block | |
| parent | f89ca166460e84620db73d4542f28d34c40a8917 (diff) | |
block: virtio_blk: don't hold spin lock during world switch
Firstly, it isn't necessary to hold lock of vblk->vq_lock
when notifying hypervisor about queued I/O.
Secondly, virtqueue_notify() will cause world switch and
it may take long time on some hypervisors(such as, qemu-arm),
so it isn't good to hold the lock and block other vCPUs.
On arm64 quad core VM(qemu-kvm), the patch can increase I/O
performance a lot with VIRTIO_RING_F_EVENT_IDX enabled:
- without the patch: 14K IOPS
- with the patch: 34K IOPS
fio script:
[global]
direct=1
bsrange=4k-4k
timeout=10
numjobs=4
ioengine=libaio
iodepth=64
filename=/dev/vdc
group_reporting=1
[f1]
rw=randread
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: stable@kernel.org # 3.13+
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'drivers/block')
| -rw-r--r-- | drivers/block/virtio_blk.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index c8f286e8d80..f63d358f3d9 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -162,6 +162,7 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) unsigned int num; const bool last = (req->cmd_flags & REQ_END) != 0; int err; + bool notify = false; BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems); @@ -214,10 +215,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) return BLK_MQ_RQ_QUEUE_ERROR; } - if (last) - virtqueue_kick(vblk->vq); - + if (last && virtqueue_kick_prepare(vblk->vq)) + notify = true; spin_unlock_irqrestore(&vblk->vq_lock, flags); + + if (notify) + virtqueue_notify(vblk->vq); return BLK_MQ_RQ_QUEUE_OK; } |