net: Add functions netif_reset_xps_queue and netif_set_xps_queue

This patch adds two functions, netif_reset_xps_queue and
netif_set_xps_queue.  The main idea behind these two functions is to
provide a mechanism through which drivers can update their defaults in
regards to XPS.

Currently no such mechanism exists and as a result we cannot use XPS for
things such as ATR which would require a basic configuration to start in
which the Tx queues are mapped to CPUs via a 1:1 mapping.  With this change
I am making it possible for drivers such as ixgbe to be able to use the XPS
feature by controlling the default configuration.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 155 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 81ff67149f62..257b29516f69 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1857,6 +1857,161 @@ static void netif_setup_tc(struct net_device *dev, unsigned int txq)
 	}
 }
 
+#ifdef CONFIG_XPS
+static DEFINE_MUTEX(xps_map_mutex);
+#define xmap_dereference(P)		\
+	rcu_dereference_protected((P), lockdep_is_held(&xps_map_mutex))
+
+void netif_reset_xps_queue(struct net_device *dev, u16 index)
+{
+	struct xps_dev_maps *dev_maps;
+	struct xps_map *map;
+	int i, pos, nonempty = 0;
+
+	mutex_lock(&xps_map_mutex);
+	dev_maps = xmap_dereference(dev->xps_maps);
+
+	if (!dev_maps)
+		goto out_no_maps;
+
+	for_each_possible_cpu(i) {
+		map = xmap_dereference(dev_maps->cpu_map[i]);
+		if (!map)
+			continue;
+
+		for (pos = 0; pos < map->len; pos++)
+			if (map->queues[pos] == index)
+				break;
+
+		if (pos < map->len) {
+			if (map->len > 1) {
+				map->queues[pos] = map->queues[--map->len];
+			} else {
+				RCU_INIT_POINTER(dev_maps->cpu_map[i], NULL);
+				kfree_rcu(map, rcu);
+				map = NULL;
+			}
+		}
+		if (map)
+			nonempty = 1;
+	}
+
+	if (!nonempty) {
+		RCU_INIT_POINTER(dev->xps_maps, NULL);
+		kfree_rcu(dev_maps, rcu);
+	}
+
+out_no_maps:
+	mutex_unlock(&xps_map_mutex);
+}
+
+int netif_set_xps_queue(struct net_device *dev, struct cpumask *mask, u16 index)
+{
+	int i, cpu, pos, map_len, alloc_len, need_set;
+	struct xps_map *map, *new_map;
+	struct xps_dev_maps *dev_maps, *new_dev_maps;
+	int nonempty = 0;
+	int numa_node_id = -2;
+	int maps_sz = max_t(unsigned int, XPS_DEV_MAPS_SIZE, L1_CACHE_BYTES);
+
+	new_dev_maps = kzalloc(maps_sz, GFP_KERNEL);
+	if (!new_dev_maps)
+		return -ENOMEM;
+
+	mutex_lock(&xps_map_mutex);
+
+	dev_maps = xmap_dereference(dev->xps_maps);
+
+	for_each_possible_cpu(cpu) {
+		map = dev_maps ?
+			xmap_dereference(dev_maps->cpu_map[cpu]) : NULL;
+		new_map = map;
+		if (map) {
+			for (pos = 0; pos < map->len; pos++)
+				if (map->queues[pos] == index)
+					break;
+			map_len = map->len;
+			alloc_len = map->alloc_len;
+		} else
+			pos = map_len = alloc_len = 0;
+
+		need_set = cpumask_test_cpu(cpu, mask) && cpu_online(cpu);
+#ifdef CONFIG_NUMA
+		if (need_set) {
+			if (numa_node_id == -2)
+				numa_node_id = cpu_to_node(cpu);
+			else if (numa_node_id != cpu_to_node(cpu))
+				numa_node_id = -1;
+		}
+#endif
+		if (need_set && pos >= map_len) {
+			/* Need to add queue to this CPU's map */
+			if (map_len >= alloc_len) {
+				alloc_len = alloc_len ?
+				    2 * alloc_len : XPS_MIN_MAP_ALLOC;
+				new_map = kzalloc_node(XPS_MAP_SIZE(alloc_len),
+						       GFP_KERNEL,
+						       cpu_to_node(cpu));
+				if (!new_map)
+					goto error;
+				new_map->alloc_len = alloc_len;
+				for (i = 0; i < map_len; i++)
+					new_map->queues[i] = map->queues[i];
+				new_map->len = map_len;
+			}
+			new_map->queues[new_map->len++] = index;
+		} else if (!need_set && pos < map_len) {
+			/* Need to remove queue from this CPU's map */
+			if (map_len > 1)
+				new_map->queues[pos] =
+				    new_map->queues[--new_map->len];
+			else
+				new_map = NULL;
+		}
+		RCU_INIT_POINTER(new_dev_maps->cpu_map[cpu], new_map);
+	}
+
+	/* Cleanup old maps */
+	for_each_possible_cpu(cpu) {
+		map = dev_maps ?
+			xmap_dereference(dev_maps->cpu_map[cpu]) : NULL;
+		if (map && xmap_dereference(new_dev_maps->cpu_map[cpu]) != map)
+			kfree_rcu(map, rcu);
+		if (new_dev_maps->cpu_map[cpu])
+			nonempty = 1;
+	}
+
+	if (nonempty) {
+		rcu_assign_pointer(dev->xps_maps, new_dev_maps);
+	} else {
+		kfree(new_dev_maps);
+		RCU_INIT_POINTER(dev->xps_maps, NULL);
+	}
+
+	if (dev_maps)
+		kfree_rcu(dev_maps, rcu);
+
+	netdev_queue_numa_node_write(netdev_get_tx_queue(dev, index),
+				     (numa_node_id >= 0) ? numa_node_id :
+				     NUMA_NO_NODE);
+
+	mutex_unlock(&xps_map_mutex);
+
+	return 0;
+error:
+	mutex_unlock(&xps_map_mutex);
+
+	if (new_dev_maps)
+		for_each_possible_cpu(i)
+			kfree(rcu_dereference_protected(
+				new_dev_maps->cpu_map[i],
+				1));
+	kfree(new_dev_maps);
+	return -ENOMEM;
+}
+EXPORT_SYMBOL(netif_set_xps_queue);
+
+#endif
 /*
  * Routine to help set real_num_tx_queues. To avoid skbs mapped to queues
  * greater then real_num_tx_queues stale skbs on the qdisc must be flushed.