[Xen-devel] [PATCH V6 net-next 4/5] xen-netfront: Add support for multiple queues

["Andrew J. Bennieston" <andrew.bennieston@xxxxxxxxxx>]

From: "Andrew J. Bennieston" <andrew.bennieston@xxxxxxxxxx>

Build on the refactoring of the previous patch to implement multiple
queues between xen-netfront and xen-netback.

Check XenStore for multi-queue support, and set up the rings and event
channels accordingly.

Write ring references and event channels to XenStore in a queue
hierarchy if appropriate, or flat when using only one queue.

Update the xennet_select_queue() function to choose the queue on which
to transmit a packet based on the skb hash result.

Signed-off-by: Andrew J. Bennieston <andrew.bennieston@xxxxxxxxxx>
Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 drivers/net/xen-netfront.c |  175 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 137 insertions(+), 38 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 4f5a431..a0dff31 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -57,6 +57,12 @@
 #include <xen/interface/memory.h>
 #include <xen/interface/grant_table.h>
 
+/* Module parameters */
+static unsigned int xennet_max_queues;
+module_param_named(max_queues, xennet_max_queues, uint, 0644);
+MODULE_PARM_DESC(max_queues,
+               "Maximum number of queues per virtual interface");
+
 static const struct ethtool_ops xennet_ethtool_ops;
 
 struct netfront_cb {
@@ -565,10 +571,22 @@ static int xennet_count_skb_frag_slots(struct sk_buff 
*skb)
        return pages;
 }
 
-static u16 xennet_select_queue(struct net_device *dev, struct sk_buff *skb)
+static u16 xennet_select_queue(struct net_device *dev, struct sk_buff *skb,
+                              void *accel_priv, select_queue_fallback_t 
fallback)
 {
-       /* Stub for later implementation of queue selection */
-       return 0;
+       struct netfront_info *info = netdev_priv(dev);
+       u32 hash;
+       u16 queue_idx;
+
+       /* First, check if there is only one queue */
+       if (info->num_queues == 1) {
+               queue_idx = 0;
+       } else {
+               hash = skb_get_hash(skb);
+               queue_idx = (u16) (((u64)hash * info->num_queues) >> 32);
+       }
+
+       return queue_idx;
 }
 
 static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
@@ -1311,7 +1329,7 @@ static struct net_device *xennet_create_dev(struct 
xenbus_device *dev)
        struct net_device *netdev;
        struct netfront_info *np;
 
-       netdev = alloc_etherdev_mq(sizeof(struct netfront_info), 1);
+       netdev = alloc_etherdev_mq(sizeof(struct netfront_info), 
xennet_max_queues);
        if (!netdev)
                return ERR_PTR(-ENOMEM);
 
@@ -1678,6 +1696,88 @@ static int xennet_init_queue(struct netfront_queue 
*queue)
        return err;
 }
 
+static int write_queue_xenstore_keys(struct netfront_queue *queue,
+                          struct xenbus_transaction *xbt, int 
write_hierarchical)
+{
+       /* Write the queue-specific keys into XenStore in the traditional
+        * way for a single queue, or in a queue subkeys for multiple
+        * queues.
+        */
+       struct xenbus_device *dev = queue->info->xbdev;
+       int err;
+       const char *message;
+       char *path;
+       size_t pathsize;
+
+       /* Choose the correct place to write the keys */
+       if (write_hierarchical) {
+               pathsize = strlen(dev->nodename) + 10;
+               path = kzalloc(pathsize, GFP_KERNEL);
+               if (!path) {
+                       err = -ENOMEM;
+                       message = "out of memory while writing ring references";
+                       goto error;
+               }
+               snprintf(path, pathsize, "%s/queue-%u",
+                               dev->nodename, queue->id);
+       } else {
+               path = (char *)dev->nodename;
+       }
+
+       /* Write ring references */
+       err = xenbus_printf(*xbt, path, "tx-ring-ref", "%u",
+                       queue->tx_ring_ref);
+       if (err) {
+               message = "writing tx-ring-ref";
+               goto error;
+       }
+
+       err = xenbus_printf(*xbt, path, "rx-ring-ref", "%u",
+                       queue->rx_ring_ref);
+       if (err) {
+               message = "writing rx-ring-ref";
+               goto error;
+       }
+
+       /* Write event channels; taking into account both shared
+        * and split event channel scenarios.
+        */
+       if (queue->tx_evtchn == queue->rx_evtchn) {
+               /* Shared event channel */
+               err = xenbus_printf(*xbt, path,
+                               "event-channel", "%u", queue->tx_evtchn);
+               if (err) {
+                       message = "writing event-channel";
+                       goto error;
+               }
+       } else {
+               /* Split event channels */
+               err = xenbus_printf(*xbt, path,
+                               "event-channel-tx", "%u", queue->tx_evtchn);
+               if (err) {
+                       message = "writing event-channel-tx";
+                       goto error;
+               }
+
+               err = xenbus_printf(*xbt, path,
+                               "event-channel-rx", "%u", queue->rx_evtchn);
+               if (err) {
+                       message = "writing event-channel-rx";
+                       goto error;
+               }
+       }
+
+       if (write_hierarchical)
+               kfree(path);
+       return 0;
+
+error:
+       if (write_hierarchical)
+               kfree(path);
+       xenbus_dev_fatal(dev, err, "%s", message);
+       return err;
+}
+
 /* Common code used when first setting up, and when resuming. */
 static int talk_to_netback(struct xenbus_device *dev,
                           struct netfront_info *info)
@@ -1687,10 +1787,18 @@ static int talk_to_netback(struct xenbus_device *dev,
        int err;
        unsigned int feature_split_evtchn;
        unsigned int i = 0;
+       unsigned int max_queues = 0;
        struct netfront_queue *queue = NULL;
 
        info->netdev->irq = 0;
 
+       /* Check if backend supports multiple queues */
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                       "multi-queue-max-queues", "%u", &max_queues);
+       if (err < 0)
+               max_queues = 1;
+       max_queues = min(max_queues, xennet_max_queues);
+
        /* Check feature-split-event-channels */
        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "feature-split-event-channels", "%u",
@@ -1706,12 +1814,13 @@ static int talk_to_netback(struct xenbus_device *dev,
        }
 
        /* Allocate array of queues */
-       info->queues = kcalloc(1, sizeof(struct netfront_queue), GFP_KERNEL);
+       info->queues = kcalloc(max_queues, sizeof(struct netfront_queue), 
GFP_KERNEL);
        if (!info->queues) {
                err = -ENOMEM;
                goto out;
        }
-       info->num_queues = 1;
+       info->num_queues = max_queues;
+       netif_set_real_num_tx_queues(info->netdev, info->num_queues);
 
        /* Create shared ring, alloc event channel -- for each queue */
        for (i = 0; i < info->num_queues; ++i) {
@@ -1749,49 +1858,35 @@ static int talk_to_netback(struct xenbus_device *dev,
        }
 
 again:
-       queue = &info->queues[0]; /* Use first queue only */
-
        err = xenbus_transaction_start(&xbt);
        if (err) {
                xenbus_dev_fatal(dev, err, "starting transaction");
                goto destroy_ring;
        }
 
-       err = xenbus_printf(xbt, dev->nodename, "tx-ring-ref", "%u",
-                           queue->tx_ring_ref);
-       if (err) {
-               message = "writing tx ring-ref";
-               goto abort_transaction;
-       }
-       err = xenbus_printf(xbt, dev->nodename, "rx-ring-ref", "%u",
-                           queue->rx_ring_ref);
-       if (err) {
-               message = "writing rx ring-ref";
-               goto abort_transaction;
-       }
-
-       if (queue->tx_evtchn == queue->rx_evtchn) {
-               err = xenbus_printf(xbt, dev->nodename,
-                                   "event-channel", "%u", queue->tx_evtchn);
-               if (err) {
-                       message = "writing event-channel";
-                       goto abort_transaction;
-               }
+       if (info->num_queues == 1) {
+               err = write_queue_xenstore_keys(&info->queues[0], &xbt, 0); /* 
flat */
+               if (err)
+                       goto abort_transaction_no_dev_fatal;
        } else {
-               err = xenbus_printf(xbt, dev->nodename,
-                                   "event-channel-tx", "%u", queue->tx_evtchn);
+               /* Write the number of queues */
+               err = xenbus_printf(xbt, dev->nodename, 
"multi-queue-num-queues",
+                               "%u", info->num_queues);
                if (err) {
-                       message = "writing event-channel-tx";
-                       goto abort_transaction;
+                       message = "writing multi-queue-num-queues";
+                       goto abort_transaction_no_dev_fatal;
                }
-               err = xenbus_printf(xbt, dev->nodename,
-                                   "event-channel-rx", "%u", queue->rx_evtchn);
-               if (err) {
-                       message = "writing event-channel-rx";
-                       goto abort_transaction;
+
+               /* Write the keys for each queue */
+               for (i = 0; i < info->num_queues; ++i) {
+                       queue = &info->queues[i];
+                       err = write_queue_xenstore_keys(queue, &xbt, 1); /* 
hierarchical */
+                       if (err)
+                               goto abort_transaction_no_dev_fatal;
                }
        }
 
+       /* The remaining keys are not queue-specific */
        err = xenbus_printf(xbt, dev->nodename, "request-rx-copy", "%u",
                            1);
        if (err) {
@@ -1841,8 +1936,9 @@ again:
        return 0;
 
  abort_transaction:
-       xenbus_transaction_end(xbt, 1);
        xenbus_dev_fatal(dev, err, "%s", message);
+abort_transaction_no_dev_fatal:
+       xenbus_transaction_end(xbt, 1);
  destroy_ring:
        xennet_disconnect_backend(info);
        kfree(info->queues);
@@ -2236,6 +2332,9 @@ static int __init netif_init(void)
 
        pr_info("Initialising Xen virtual ethernet driver\n");
 
+       /* Allow as many queues as there are CPUs, by default */
+       xennet_max_queues = num_online_cpus();
+
        return xenbus_register_frontend(&netfront_driver);
 }
 module_init(netif_init);
-- 
1.7.10.4


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