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[Xen-devel] [PATCH v3 6/9] xen/blkfront: negotiate the number of hw queues/rings with backend



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@xxxxxxxxxx>
---
 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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