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Date: Sun, 22 Jun 2014 13:24:48 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Ming Lei <ming.lei@...onical.com>
Cc: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
Rusty Russell <rusty@...tcorp.com.au>,
linux-api@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
Stefan Hajnoczi <stefanha@...hat.com>,
Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v1 2/2] block: virtio-blk: support multi virt queues per
virtio-blk device
On Fri, Jun 20, 2014 at 11:29:40PM +0800, Ming Lei wrote:
> Firstly this patch supports more than one virtual queues for virtio-blk
> device.
>
> Secondly this patch maps the virtual queue to blk-mq's hardware queue.
>
> With this approach, both scalability and performance can be improved.
>
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
> drivers/block/virtio_blk.c | 70 +++++++++++++++++++++++++++++++-------------
> 1 file changed, 50 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index f63d358..7c3d686 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -16,6 +16,8 @@
>
> #define PART_BITS 4
>
> +#define MAX_NUM_VQ 16
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
Does it work much worse if we just use as many queues as
hardware supports, allocating as much memory as necessary?
> @@ -24,8 +26,8 @@ static struct workqueue_struct *virtblk_wq;
> struct virtio_blk
> {
> struct virtio_device *vdev;
> - struct virtqueue *vq;
> - spinlock_t vq_lock;
> + struct virtqueue *vq[MAX_NUM_VQ];
> + spinlock_t vq_lock[MAX_NUM_VQ];
array of struct {
*vq;
spinlock_t lock;
}
would use more memory but would get us better locality.
It might even make sense to add padding to avoid
cacheline sharing between two unrelated VQs.
Want to try?
>
> /* The disk structure for the kernel. */
> struct gendisk *disk;
> @@ -47,6 +49,9 @@ struct virtio_blk
>
> /* Ida index - used to track minor number allocations. */
> int index;
> +
> + /* num of vqs */
> + int num_vqs;
> };
>
> struct virtblk_req
> @@ -133,14 +138,15 @@ static void virtblk_done(struct virtqueue *vq)
> {
> struct virtio_blk *vblk = vq->vdev->priv;
> bool req_done = false;
> + int qid = vq->index;
> struct virtblk_req *vbr;
> unsigned long flags;
> unsigned int len;
>
> - spin_lock_irqsave(&vblk->vq_lock, flags);
> + spin_lock_irqsave(&vblk->vq_lock[qid], flags);
> do {
> virtqueue_disable_cb(vq);
> - while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
> + while ((vbr = virtqueue_get_buf(vblk->vq[qid], &len)) != NULL) {
> blk_mq_complete_request(vbr->req);
> req_done = true;
> }
> @@ -151,7 +157,7 @@ static void virtblk_done(struct virtqueue *vq)
> /* In case queue is stopped waiting for more buffers. */
> if (req_done)
> blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
> - spin_unlock_irqrestore(&vblk->vq_lock, flags);
> + spin_unlock_irqrestore(&vblk->vq_lock[qid], flags);
> }
>
> static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
> @@ -160,6 +166,7 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
> struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
> unsigned long flags;
> unsigned int num;
> + int qid = hctx->queue_num;
> const bool last = (req->cmd_flags & REQ_END) != 0;
> int err;
> bool notify = false;
> @@ -202,12 +209,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
> vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
> }
>
> - spin_lock_irqsave(&vblk->vq_lock, flags);
> - err = __virtblk_add_req(vblk->vq, vbr, vbr->sg, num);
> + spin_lock_irqsave(&vblk->vq_lock[qid], flags);
> + err = __virtblk_add_req(vblk->vq[qid], vbr, vbr->sg, num);
> if (err) {
> - virtqueue_kick(vblk->vq);
> + virtqueue_kick(vblk->vq[qid]);
> blk_mq_stop_hw_queue(hctx);
> - spin_unlock_irqrestore(&vblk->vq_lock, flags);
> + spin_unlock_irqrestore(&vblk->vq_lock[qid], flags);
> /* Out of mem doesn't actually happen, since we fall back
> * to direct descriptors */
> if (err == -ENOMEM || err == -ENOSPC)
> @@ -215,12 +222,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
> return BLK_MQ_RQ_QUEUE_ERROR;
> }
>
> - if (last && virtqueue_kick_prepare(vblk->vq))
> + if (last && virtqueue_kick_prepare(vblk->vq[qid]))
> notify = true;
> - spin_unlock_irqrestore(&vblk->vq_lock, flags);
> + spin_unlock_irqrestore(&vblk->vq_lock[qid], flags);
>
> if (notify)
> - virtqueue_notify(vblk->vq);
> + virtqueue_notify(vblk->vq[qid]);
> return BLK_MQ_RQ_QUEUE_OK;
> }
>
> @@ -377,12 +384,35 @@ static void virtblk_config_changed(struct virtio_device *vdev)
> static int init_vq(struct virtio_blk *vblk)
> {
> int err = 0;
> + int i;
> + vq_callback_t *callbacks[MAX_NUM_VQ];
> + const char *names[MAX_NUM_VQ];
> + unsigned short num_vqs;
> + struct virtio_device *vdev = vblk->vdev;
>
> - /* We expect one virtqueue, for output. */
> - vblk->vq = virtio_find_single_vq(vblk->vdev, virtblk_done, "requests");
> - if (IS_ERR(vblk->vq))
> - err = PTR_ERR(vblk->vq);
> + err = virtio_cread_feature(vdev, VIRTIO_BLK_F_MQ,
> + struct virtio_blk_config, num_queues,
> + &num_vqs);
> + if (err)
> + num_vqs = 1;
> + if (num_vqs > MAX_NUM_VQ)
> + num_vqs = MAX_NUM_VQ;
>
> + for (i = 0; i < num_vqs; i++) {
> + callbacks[i] = virtblk_done;
> + names[i] = "requests";
> + }
> +
This will name all VQs the same which makes debugging harder.
Better give each one a distinct name.
> + /* Discover virtqueues and write information to configuration. */
> + err = vdev->config->find_vqs(vdev, num_vqs, vblk->vq,
> + callbacks, names);
> + if (err)
> + goto out;
> +
> + for (i = 0; i < num_vqs; i++)
> + spin_lock_init(&vblk->vq_lock[i]);
> + vblk->num_vqs = num_vqs;
> +out:
> return err;
> }
>
> @@ -551,7 +581,6 @@ static int virtblk_probe(struct virtio_device *vdev)
> err = init_vq(vblk);
> if (err)
> goto out_free_vblk;
> - spin_lock_init(&vblk->vq_lock);
>
> /* FIXME: How many partitions? How long is a piece of string? */
> vblk->disk = alloc_disk(1 << PART_BITS);
> @@ -562,7 +591,7 @@ static int virtblk_probe(struct virtio_device *vdev)
>
> /* Default queue sizing is to fill the ring. */
> if (!virtblk_queue_depth) {
> - virtblk_queue_depth = vblk->vq->num_free;
> + virtblk_queue_depth = vblk->vq[0]->num_free;
> /* ... but without indirect descs, we use 2 descs per req */
> if (!virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC))
> virtblk_queue_depth /= 2;
> @@ -570,7 +599,6 @@ static int virtblk_probe(struct virtio_device *vdev)
>
> memset(&vblk->tag_set, 0, sizeof(vblk->tag_set));
> vblk->tag_set.ops = &virtio_mq_ops;
> - vblk->tag_set.nr_hw_queues = 1;
> vblk->tag_set.queue_depth = virtblk_queue_depth;
> vblk->tag_set.numa_node = NUMA_NO_NODE;
> vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
> @@ -578,6 +606,7 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct virtblk_req) +
> sizeof(struct scatterlist) * sg_elems;
> vblk->tag_set.driver_data = vblk;
> + vblk->tag_set.nr_hw_queues = vblk->num_vqs;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
> @@ -777,7 +806,8 @@ static const struct virtio_device_id id_table[] = {
> static unsigned int features[] = {
> VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
> VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE, VIRTIO_BLK_F_SCSI,
> - VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE
> + VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
> + VIRTIO_BLK_F_MQ,
> };
>
> static struct virtio_driver virtio_blk = {
> --
> 1.7.9.5
--
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