On Fri, May 30, 2014 at 10:49:29AM +0800, Ming Lei wrote: > 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> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > --- > 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
