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@xxxxxxxxxxxxxxx> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx> --- drivers/block/virtio_blk.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 9f340fa..a6f5424 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; } -- 1.7.9.5 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
