Commit fc4324b4 authored Mar 19, 2014 by Rusty Russell

virtio-blk: base queue-depth on virtqueue ringsize or module param



Venkatash spake thus:

  virtio-blk set the default queue depth to 64 requests, which was
  insufficient for high-IOPS devices. Instead set the blk-queue depth to
  the device's virtqueue depth divided by two (each I/O requires at least
  two VQ entries).

But behold, Ted added a module parameter:

  Also allow the queue depth to be something which can be set at module
  load time or via a kernel boot-time parameter, for
  testing/benchmarking purposes.

And I rewrote it substantially, mainly to take
VIRTIO_RING_F_INDIRECT_DESC into account.

As QEMU sets the vq size for PCI to 128, Venkatash's patch wouldn't
have made a change.  This version does (since QEMU also offers
VIRTIO_RING_F_INDIRECT_DESC.

Inspired-by: "Theodore Ts'o" <tytso@mit.edu>
Based-on-the-true-story-of: Venkatesh Srinivas <venkateshs@google.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtio-dev@lists.oasis-open.org
Cc: virtualization@lists.linux-foundation.org
Cc: Frank Swiderski <fes@google.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

parent b1ee30ae

drivers/block/virtio_blk.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -491,10 +491,11 @@ static struct blk_mq_ops virtio_mq_ops = {
		static struct blk_mq_reg virtio_mq_reg = {
		.ops = &virtio_mq_ops,
		.nr_hw_queues = 1,
		.queue_depth = 64,
		.queue_depth = 0, /* Set in virtblk_probe */
		.numa_node = NUMA_NO_NODE,
		.flags = BLK_MQ_F_SHOULD_MERGE,
		};
		module_param_named(queue_depth, virtio_mq_reg.queue_depth, uint, 0444);

		static void virtblk_init_vbr(void data, struct blk_mq_hw_ctx hctx,
		struct request *rq, unsigned int nr)
		@@ -558,6 +559,13 @@ static int virtblk_probe(struct virtio_device *vdev)
		goto out_free_vq;
		}

		/* Default queue sizing is to fill the ring. */
		if (!virtio_mq_reg.queue_depth) {
		virtio_mq_reg.queue_depth = vblk->vq->num_free;
		/* ... but without indirect descs, we use 2 descs per req */
		if (!virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC))
		virtio_mq_reg.queue_depth /= 2;
		}
		virtio_mq_reg.cmd_size =
		sizeof(struct virtblk_req) +
		sizeof(struct scatterlist) * sg_elems;