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    Subject[PATCH v3 6/9] xen/blkfront: negotiate the number of hw queues/rings with backend
    Date
    The max number of hardware queues for xen/blkfront is set by parameter
    'max_queues', while the number xen/blkback supported is notified through
    xenstore("multi-queue-max-queues").

    The negotiated number was the smaller one, and was written back to
    xen/blkback as "multi-queue-num-queues".

    Signed-off-by: Bob Liu <bob.liu@oracle.com>
    ---
    drivers/block/xen-blkfront.c | 142 ++++++++++++++++++++++++++++++++----------
    1 file changed, 108 insertions(+), 34 deletions(-)

    diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
    index 1cae76b..1aa66c9 100644
    --- a/drivers/block/xen-blkfront.c
    +++ b/drivers/block/xen-blkfront.c
    @@ -107,6 +107,10 @@ static unsigned int xen_blkif_max_ring_order;
    module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, S_IRUGO);
    MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring");

    +static unsigned int xen_blkif_max_queues;
    +module_param_named(max_queues, xen_blkif_max_queues, uint, S_IRUGO);
    +MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues/rings per virtual disk");
    +
    #define BLK_RING_SIZE(dinfo) __CONST_RING_SIZE(blkif, PAGE_SIZE * (dinfo)->pages_per_ring)
    #define BLK_MAX_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE * XENBUS_MAX_RING_PAGES)
    /*
    @@ -114,6 +118,7 @@ MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the
    * characters are enough. Define to 20 to keep consist with backend.
    */
    #define RINGREF_NAME_LEN (20)
    +#define QUEUE_NAME_LEN (12)

    /*
    * Per-ring info.
    @@ -687,7 +692,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,

    memset(&dinfo->tag_set, 0, sizeof(dinfo->tag_set));
    dinfo->tag_set.ops = &blkfront_mq_ops;
    - dinfo->tag_set.nr_hw_queues = 1;
    + dinfo->tag_set.nr_hw_queues = dinfo->nr_rings;
    dinfo->tag_set.queue_depth = BLK_RING_SIZE(dinfo);
    dinfo->tag_set.numa_node = NUMA_NO_NODE;
    dinfo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
    @@ -1350,6 +1355,51 @@ fail:
    return err;
    }

    +static int write_per_ring_nodes(struct xenbus_transaction xbt,
    + struct blkfront_ring_info *rinfo, const char *dir)
    +{
    + int err, i;
    + const char *message = NULL;
    + struct blkfront_dev_info *dinfo = rinfo->dinfo;
    +
    + if (dinfo->pages_per_ring == 1) {
    + err = xenbus_printf(xbt, dir, "ring-ref", "%u", rinfo->ring_ref[0]);
    + if (err) {
    + message = "writing ring-ref";
    + goto abort_transaction;
    + }
    + pr_info("%s: write ring-ref:%d\n", dir, rinfo->ring_ref[0]);
    + } else {
    + for (i = 0; i < dinfo->pages_per_ring; i++) {
    + char ring_ref_name[RINGREF_NAME_LEN];
    +
    + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
    + err = xenbus_printf(xbt, dir, ring_ref_name,
    + "%u", rinfo->ring_ref[i]);
    + if (err) {
    + message = "writing ring-ref";
    + goto abort_transaction;
    + }
    + pr_info("%s: write ring-ref:%d\n", dir, rinfo->ring_ref[i]);
    + }
    + }
    +
    + err = xenbus_printf(xbt, dir, "event-channel", "%u", rinfo->evtchn);
    + if (err) {
    + message = "writing event-channel";
    + goto abort_transaction;
    + }
    + pr_info("%s: write event-channel:%d\n", dir, rinfo->evtchn);
    +
    + return 0;
    +
    +abort_transaction:
    + xenbus_transaction_end(xbt, 1);
    + if (message)
    + xenbus_dev_fatal(dinfo->xbdev, err, "%s", message);
    +
    + return err;
    +}

    /* Common code used when first setting up, and when resuming. */
    static int talk_to_blkback(struct xenbus_device *dev,
    @@ -1386,45 +1436,51 @@ again:
    goto out;
    }

    + if (dinfo->pages_per_ring > 1) {
    + err = xenbus_printf(xbt, dev->nodename, "ring-page-order", "%u",
    + ring_page_order);
    + if (err) {
    + message = "writing ring-page-order";
    + goto abort_transaction;
    + }
    + }
    +
    + /* We already got the number of queues in _probe */
    if (dinfo->nr_rings == 1) {
    rinfo = &dinfo->rinfo[0];

    - if (dinfo->pages_per_ring == 1) {
    - err = xenbus_printf(xbt, dev->nodename,
    - "ring-ref", "%u", rinfo->ring_ref[0]);
    - if (err) {
    - message = "writing ring-ref";
    - goto abort_transaction;
    - }
    - } else {
    - err = xenbus_printf(xbt, dev->nodename,
    - "ring-page-order", "%u", ring_page_order);
    - if (err) {
    - message = "writing ring-page-order";
    - goto abort_transaction;
    - }
    -
    - for (i = 0; i < dinfo->pages_per_ring; i++) {
    - char ring_ref_name[RINGREF_NAME_LEN];
    + err = write_per_ring_nodes(xbt, &dinfo->rinfo[0], dev->nodename);
    + if (err)
    + goto out;
    + } else {
    + char *path;
    + size_t pathsize;

    - snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
    - err = xenbus_printf(xbt, dev->nodename, ring_ref_name,
    - "%u", rinfo->ring_ref[i]);
    - if (err) {
    - message = "writing ring-ref";
    - goto abort_transaction;
    - }
    - }
    - }
    - err = xenbus_printf(xbt, dev->nodename,
    - "event-channel", "%u", rinfo->evtchn);
    + err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues", "%u",
    + dinfo->nr_rings);
    if (err) {
    - message = "writing event-channel";
    + message = "writing multi-queue-num-queues";
    goto abort_transaction;
    }
    - } else {
    - /* Not supported at this stage */
    - goto abort_transaction;
    +
    + pathsize = strlen(dev->nodename) + QUEUE_NAME_LEN;
    + path = kzalloc(pathsize, GFP_KERNEL);
    + if (!path) {
    + err = -ENOMEM;
    + message = "ENOMEM while writing ring references";
    + goto abort_transaction;
    + }
    +
    + for (i = 0; i < dinfo->nr_rings; i++) {
    + memset(path, 0, pathsize);
    + snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
    + err = write_per_ring_nodes(xbt, &dinfo->rinfo[i], path);
    + if (err) {
    + kfree(path);
    + goto out;
    + }
    + }
    + kfree(path);
    }

    err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
    @@ -1480,6 +1536,7 @@ static int blkfront_probe(struct xenbus_device *dev,
    int err, vdevice, r_index;
    struct blkfront_dev_info *dinfo;
    struct blkfront_ring_info *rinfo;
    + unsigned int back_max_queues = 0;

    /* FIXME: Use dynamic device id if this is not set. */
    err = xenbus_scanf(XBT_NIL, dev->nodename,
    @@ -1534,7 +1591,17 @@ static int blkfront_probe(struct xenbus_device *dev,
    dinfo->vdevice = vdevice;
    dinfo->connected = BLKIF_STATE_DISCONNECTED;

    - dinfo->nr_rings = 1;
    + /* Check if backend supports multiple queues */
    + err = xenbus_scanf(XBT_NIL, dinfo->xbdev->otherend,
    + "multi-queue-max-queues", "%u", &back_max_queues);
    + if (err < 0)
    + back_max_queues = 1;
    +
    + dinfo->nr_rings = min(back_max_queues, xen_blkif_max_queues);
    + if (dinfo->nr_rings <= 0)
    + dinfo->nr_rings = 1;
    + pr_info("dinfo->nr_rings:%u, backend support max-queues:%u\n", dinfo->nr_rings, back_max_queues);
    +
    dinfo->rinfo = kzalloc(sizeof(*rinfo) * dinfo->nr_rings, GFP_KERNEL);
    if (!dinfo->rinfo) {
    xenbus_dev_fatal(dev, -ENOMEM, "allocating ring_info structure");
    @@ -2257,6 +2324,7 @@ static struct xenbus_driver blkfront_driver = {
    static int __init xlblk_init(void)
    {
    int ret;
    + int nr_cpus = num_online_cpus();

    if (!xen_domain())
    return -ENODEV;
    @@ -2267,6 +2335,12 @@ static int __init xlblk_init(void)
    xen_blkif_max_ring_order = 0;
    }

    + if (xen_blkif_max_queues > nr_cpus) {
    + pr_info("Invalid max_queues (%d), will use default max: %d.\n",
    + xen_blkif_max_queues, nr_cpus);
    + xen_blkif_max_queues = nr_cpus;
    + }
    +
    if (!xen_has_pv_disk_devices())
    return -ENODEV;

    --
    1.7.10.4


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