diff options
author | Ming Lei <ming.lei@canonical.com> | 2014-05-29 22:49:29 -0400 |
---|---|---|
committer | Jens Axboe <axboe@fb.com> | 2014-05-30 10:19:39 -0400 |
commit | e8edca6f7f92234202d6dd163c118ef495244d7c (patch) | |
tree | 3546ab7cd1062b0cad3007818c08e468aa189a0c | |
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>
-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 c8f286e8d80f..f63d358f3d93 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) | |||
162 | unsigned int num; | 162 | unsigned int num; |
163 | const bool last = (req->cmd_flags & REQ_END) != 0; | 163 | const bool last = (req->cmd_flags & REQ_END) != 0; |
164 | int err; | 164 | int err; |
165 | bool notify = false; | ||
165 | 166 | ||
166 | BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems); | 167 | BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems); |
167 | 168 | ||
@@ -214,10 +215,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) | |||
214 | return BLK_MQ_RQ_QUEUE_ERROR; | 215 | return BLK_MQ_RQ_QUEUE_ERROR; |
215 | } | 216 | } |
216 | 217 | ||
217 | if (last) | 218 | if (last && virtqueue_kick_prepare(vblk->vq)) |
218 | virtqueue_kick(vblk->vq); | 219 | notify = true; |
219 | |||
220 | spin_unlock_irqrestore(&vblk->vq_lock, flags); | 220 | spin_unlock_irqrestore(&vblk->vq_lock, flags); |
221 | |||
222 | if (notify) | ||
223 | virtqueue_notify(vblk->vq); | ||
221 | return BLK_MQ_RQ_QUEUE_OK; | 224 | return BLK_MQ_RQ_QUEUE_OK; |
222 | } | 225 | } |
223 | 226 | ||