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>
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index a2db9ed..19622227 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -491,10 +491,11 @@
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 @@
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;