[net-next PATCH 0/3] Add support for XPS when using DCB

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Revision v1 of 2 in this series.

9 messages, 4 authors, 2016-10-28 · open the first message on its own page

[net-next PATCH 0/3] Add support for XPS when using DCB

From: Alexander Duyck <hidden>
Date: 2016-10-27 21:40:48 

This patch series enables proper isolation between traffic classes when
using XPS while DCB is enabled.  Previously enabling XPS would cause the
traffic to be potentially pulled from one traffic class into another on
egress.  This change essentially multiplies the XPS map by the number of
traffic classes and allows us to do a lookup per traffic class for a given
CPU.

To guarantee the isolation I invalidate the XPS map for any queues that are
moved from one traffic class to another, or if we change the number of
traffic classes.

---

Alexander Duyck (3):
      net: Move functions for configuring traffic classes out of inline headers
      net: Refactor removal of queues from XPS map and apply on num_tc changes
      net: Add support for XPS with QoS via traffic classes


 include/linux/netdevice.h |   36 +------
 net/core/dev.c            |  228 +++++++++++++++++++++++++++++++++++----------
 net/core/net-sysfs.c      |   31 ++++--
 3 files changed, 202 insertions(+), 93 deletions(-)

[net-next PATCH 1/3] net: Move functions for configuring traffic classes out of inline headers

From: Alexander Duyck <hidden>
Date: 2016-10-27 21:40:49 

The functions for configuring the traffic class to queue mappings have
other effects that need to be addressed.  Instead of trying to export a
bunch of new functions just relocate the functions so that we can
instrument them directly with the functionality they will need.

Signed-off-by: Alexander Duyck <redacted>
---
 include/linux/netdevice.h |   31 +++----------------------------
 net/core/dev.c            |   29 +++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 28 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 458c876..d045432 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1920,34 +1920,9 @@ int netdev_set_prio_tc_map(struct net_device *dev, u8 prio, u8 tc)
 	return 0;
 }
 
-static inline
-void netdev_reset_tc(struct net_device *dev)
-{
-	dev->num_tc = 0;
-	memset(dev->tc_to_txq, 0, sizeof(dev->tc_to_txq));
-	memset(dev->prio_tc_map, 0, sizeof(dev->prio_tc_map));
-}
-
-static inline
-int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset)
-{
-	if (tc >= dev->num_tc)
-		return -EINVAL;
-
-	dev->tc_to_txq[tc].count = count;
-	dev->tc_to_txq[tc].offset = offset;
-	return 0;
-}
-
-static inline
-int netdev_set_num_tc(struct net_device *dev, u8 num_tc)
-{
-	if (num_tc > TC_MAX_QUEUE)
-		return -EINVAL;
-
-	dev->num_tc = num_tc;
-	return 0;
-}
+void netdev_reset_tc(struct net_device *dev);
+int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset);
+int netdev_set_num_tc(struct net_device *dev, u8 num_tc);
 
 static inline
 int netdev_get_num_tc(struct net_device *dev)
diff --git a/net/core/dev.c b/net/core/dev.c
index f55fb45..d4d45bf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2173,6 +2173,35 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 EXPORT_SYMBOL(netif_set_xps_queue);
 
 #endif
+void netdev_reset_tc(struct net_device *dev)
+{
+	dev->num_tc = 0;
+	memset(dev->tc_to_txq, 0, sizeof(dev->tc_to_txq));
+	memset(dev->prio_tc_map, 0, sizeof(dev->prio_tc_map));
+}
+EXPORT_SYMBOL(netdev_reset_tc);
+
+int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset)
+{
+	if (tc >= dev->num_tc)
+		return -EINVAL;
+
+	dev->tc_to_txq[tc].count = count;
+	dev->tc_to_txq[tc].offset = offset;
+	return 0;
+}
+EXPORT_SYMBOL(netdev_set_tc_queue);
+
+int netdev_set_num_tc(struct net_device *dev, u8 num_tc)
+{
+	if (num_tc > TC_MAX_QUEUE)
+		return -EINVAL;
+
+	dev->num_tc = num_tc;
+	return 0;
+}
+EXPORT_SYMBOL(netdev_set_num_tc);
+
 /*
  * 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.

[net-next PATCH 2/3] net: Refactor removal of queues from XPS map and apply on num_tc changes

From: Alexander Duyck <hidden>
Date: 2016-10-27 21:40:51 

This patch updates the code for removing queues from the XPS map and makes
it so that we can apply the code any time we change either the number of
traffic classes or the mapping of a given block of queues.  This way we
avoid having queues pulling traffic from a foreign traffic class.

Signed-off-by: Alexander Duyck <redacted>
---
 net/core/dev.c |   79 ++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 56 insertions(+), 23 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index d4d45bf..d124081 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1953,32 +1953,56 @@ static void netif_setup_tc(struct net_device *dev, unsigned int txq)
 #define xmap_dereference(P)		\
 	rcu_dereference_protected((P), lockdep_is_held(&xps_map_mutex))
 
-static struct xps_map *remove_xps_queue(struct xps_dev_maps *dev_maps,
-					int cpu, u16 index)
+static bool remove_xps_queue(struct xps_dev_maps *dev_maps,
+			     int tci, u16 index)
 {
 	struct xps_map *map = NULL;
 	int pos;
 
 	if (dev_maps)
-		map = xmap_dereference(dev_maps->cpu_map[cpu]);
+		map = xmap_dereference(dev_maps->cpu_map[tci]);
+	if (!map)
+		return false;
 
-	for (pos = 0; map && pos < map->len; pos++) {
-		if (map->queues[pos] == index) {
-			if (map->len > 1) {
-				map->queues[pos] = map->queues[--map->len];
-			} else {
-				RCU_INIT_POINTER(dev_maps->cpu_map[cpu], NULL);
-				kfree_rcu(map, rcu);
-				map = NULL;
-			}
+	for (pos = map->len; pos--;) {
+		if (map->queues[pos] != index)
+			continue;
+
+		if (map->len > 1) {
+			map->queues[pos] = map->queues[--map->len];
 			break;
 		}
+
+		RCU_INIT_POINTER(dev_maps->cpu_map[tci], NULL);
+		kfree_rcu(map, rcu);
+		return false;
 	}
 
-	return map;
+	return true;
 }
 
-static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
+static bool remove_xps_queue_cpu(struct net_device *dev,
+				 struct xps_dev_maps *dev_maps,
+				 int cpu, u16 offset, u16 count)
+{
+	bool active = false;
+	int i;
+
+	count += offset;
+	i = count;
+
+	do {
+		if (i-- == offset) {
+			active = true;
+			break;
+		}
+	} while (remove_xps_queue(dev_maps, cpu, i));
+
+	return active;
+}
+
+static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
+				   u16 count)
 {
 	struct xps_dev_maps *dev_maps;
 	int cpu, i;
@@ -1990,21 +2014,16 @@ static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
 	if (!dev_maps)
 		goto out_no_maps;
 
-	for_each_possible_cpu(cpu) {
-		for (i = index; i < dev->num_tx_queues; i++) {
-			if (!remove_xps_queue(dev_maps, cpu, i))
-				break;
-		}
-		if (i == dev->num_tx_queues)
-			active = true;
-	}
+	for_each_possible_cpu(cpu)
+		active |= remove_xps_queue_cpu(dev, dev_maps, cpu, offset,
+					       count);
 
 	if (!active) {
 		RCU_INIT_POINTER(dev->xps_maps, NULL);
 		kfree_rcu(dev_maps, rcu);
 	}
 
-	for (i = index; i < dev->num_tx_queues; i++)
+	for (i = offset + (count - 1); count--; i--)
 		netdev_queue_numa_node_write(netdev_get_tx_queue(dev, i),
 					     NUMA_NO_NODE);
 
@@ -2012,6 +2031,11 @@ static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
 	mutex_unlock(&xps_map_mutex);
 }
 
+static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
+{
+	netif_reset_xps_queues(dev, index, dev->num_tx_queues - index);
+}
+
 static struct xps_map *expand_xps_map(struct xps_map *map,
 				      int cpu, u16 index)
 {
@@ -2175,6 +2199,9 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 #endif
 void netdev_reset_tc(struct net_device *dev)
 {
+#ifdef CONFIG_XPS
+	netif_reset_xps_queues_gt(dev, 0);
+#endif
 	dev->num_tc = 0;
 	memset(dev->tc_to_txq, 0, sizeof(dev->tc_to_txq));
 	memset(dev->prio_tc_map, 0, sizeof(dev->prio_tc_map));
@@ -2186,6 +2213,9 @@ int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset)
 	if (tc >= dev->num_tc)
 		return -EINVAL;
 
+#ifdef CONFIG_XPS
+	netif_reset_xps_queues(dev, offset, count);
+#endif
 	dev->tc_to_txq[tc].count = count;
 	dev->tc_to_txq[tc].offset = offset;
 	return 0;
@@ -2197,6 +2227,9 @@ int netdev_set_num_tc(struct net_device *dev, u8 num_tc)
 	if (num_tc > TC_MAX_QUEUE)
 		return -EINVAL;
 
+#ifdef CONFIG_XPS
+	netif_reset_xps_queues_gt(dev, 0);
+#endif
 	dev->num_tc = num_tc;
 	return 0;
 }

[net-next PATCH 3/3] net: Add support for XPS with QoS via traffic classes

From: Alexander Duyck <hidden>
Date: 2016-10-27 21:41:02 

This patch adds support for setting and using XPS when QoS via traffic
classes is enabled.  With this change we will factor in the priority and
traffic class mapping of the packet and use that information to correctly
select the queue.

This allows us to define a set of queues for a given traffic class via
mqprio and then configure the XPS mapping for those queues so that the
traffic flows can avoid head-of-line blocking between the individual CPUs
if so desired.

Signed-off-by: Alexander Duyck <redacted>
---
 include/linux/netdevice.h |    5 +-
 net/core/dev.c            |  136 +++++++++++++++++++++++++++++++++------------
 net/core/net-sysfs.c      |   31 +++++++---
 3 files changed, 122 insertions(+), 50 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d045432..56f90f7 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -732,8 +732,8 @@ struct xps_dev_maps {
 	struct rcu_head rcu;
 	struct xps_map __rcu *cpu_map[0];
 };
-#define XPS_DEV_MAPS_SIZE (sizeof(struct xps_dev_maps) +		\
-    (nr_cpu_ids * sizeof(struct xps_map *)))
+#define XPS_DEV_MAPS_SIZE(_tcs) (sizeof(struct xps_dev_maps) +		\
+	(nr_cpu_ids * (_tcs) * sizeof(struct xps_map *)))
 #endif /* CONFIG_XPS */
 
 #define TC_MAX_QUEUE	16
@@ -1920,6 +1920,7 @@ int netdev_set_prio_tc_map(struct net_device *dev, u8 prio, u8 tc)
 	return 0;
 }
 
+int netdev_txq_to_tc(struct net_device *dev, unsigned int txq);
 void netdev_reset_tc(struct net_device *dev);
 int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset);
 int netdev_set_num_tc(struct net_device *dev, u8 num_tc);
diff --git a/net/core/dev.c b/net/core/dev.c
index d124081..37c1096 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1948,6 +1948,23 @@ static void netif_setup_tc(struct net_device *dev, unsigned int txq)
 	}
 }
 
+int netdev_txq_to_tc(struct net_device *dev, unsigned int txq)
+{
+	if (dev->num_tc) {
+		struct netdev_tc_txq *tc = &dev->tc_to_txq[0];
+		int i;
+
+		for (i = 0; i < TC_MAX_QUEUE; i++, tc++) {
+			if ((txq - tc->offset) < tc->count)
+				return i;
+		}
+
+		return -1;
+	}
+
+	return 0;
+}
+
 #ifdef CONFIG_XPS
 static DEFINE_MUTEX(xps_map_mutex);
 #define xmap_dereference(P)		\
@@ -1985,18 +2002,22 @@ static bool remove_xps_queue_cpu(struct net_device *dev,
 				 struct xps_dev_maps *dev_maps,
 				 int cpu, u16 offset, u16 count)
 {
+	int tc = dev->num_tc ? : 1;
 	bool active = false;
-	int i;
+	int tci;
 
 	count += offset;
-	i = count;
 
-	do {
-		if (i-- == offset) {
-			active = true;
-			break;
-		}
-	} while (remove_xps_queue(dev_maps, cpu, i));
+	for (tci = cpu * tc; tc--; tci++) {
+		int i = count;
+
+		do {
+			if (i-- == offset) {
+				active = true;
+				break;
+			}
+		} while (remove_xps_queue(dev_maps, tci, i));
+	}
 
 	return active;
 }
@@ -2075,20 +2096,28 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 			u16 index)
 {
 	struct xps_dev_maps *dev_maps, *new_dev_maps = NULL;
+	int i, cpu, tci, numa_node_id = -2;
+	int maps_sz, num_tc = 1, tc = 0;
 	struct xps_map *map, *new_map;
-	int maps_sz = max_t(unsigned int, XPS_DEV_MAPS_SIZE, L1_CACHE_BYTES);
-	int cpu, numa_node_id = -2;
 	bool active = false;
 
+	if (dev->num_tc) {
+		num_tc = dev->num_tc;
+		tc = netdev_txq_to_tc(dev, index);
+		if (tc < 0)
+			return -EINVAL;
+	}
+
+	maps_sz = XPS_DEV_MAPS_SIZE(num_tc);
+	if (maps_sz < L1_CACHE_BYTES)
+		maps_sz = L1_CACHE_BYTES;
+
 	mutex_lock(&xps_map_mutex);
 
 	dev_maps = xmap_dereference(dev->xps_maps);
 
 	/* allocate memory for queue storage */
-	for_each_online_cpu(cpu) {
-		if (!cpumask_test_cpu(cpu, mask))
-			continue;
-
+	for_each_cpu_and(cpu, cpu_online_mask, mask) {
 		if (!new_dev_maps)
 			new_dev_maps = kzalloc(maps_sz, GFP_KERNEL);
 		if (!new_dev_maps) {
@@ -2096,25 +2125,35 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 			return -ENOMEM;
 		}
 
-		map = dev_maps ? xmap_dereference(dev_maps->cpu_map[cpu]) :
+		tci = cpu * num_tc + tc;
+		map = dev_maps ? xmap_dereference(dev_maps->cpu_map[tci]) :
 				 NULL;
 
 		map = expand_xps_map(map, cpu, index);
 		if (!map)
 			goto error;
 
-		RCU_INIT_POINTER(new_dev_maps->cpu_map[cpu], map);
+		RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
 	}
 
 	if (!new_dev_maps)
 		goto out_no_new_maps;
 
 	for_each_possible_cpu(cpu) {
+		/* copy maps belonging to foreign traffic classes */
+		tci = cpu * num_tc;
+		for (i = 0; dev_maps && i < tc; i++, tci++) {
+			/* fill in the new device map from the old device map */
+			map = xmap_dereference(dev_maps->cpu_map[tci]);
+			RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
+		}
+
+		tci = cpu * num_tc + tc;
 		if (cpumask_test_cpu(cpu, mask) && cpu_online(cpu)) {
 			/* add queue to CPU maps */
 			int pos = 0;
 
-			map = xmap_dereference(new_dev_maps->cpu_map[cpu]);
+			map = xmap_dereference(new_dev_maps->cpu_map[tci]);
 			while ((pos < map->len) && (map->queues[pos] != index))
 				pos++;
 
@@ -2128,26 +2167,37 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 #endif
 		} else if (dev_maps) {
 			/* fill in the new device map from the old device map */
-			map = xmap_dereference(dev_maps->cpu_map[cpu]);
-			RCU_INIT_POINTER(new_dev_maps->cpu_map[cpu], map);
+			map = xmap_dereference(dev_maps->cpu_map[tci]);
+			RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
 		}
 
+		/* copy maps belonging to foreign traffic classes */
+		for (i = tc, tci++; dev_maps && (++i < num_tc); tci++) {
+			/* fill in the new device map from the old device map */
+			map = xmap_dereference(dev_maps->cpu_map[tci]);
+			RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
+		}
 	}
 
 	rcu_assign_pointer(dev->xps_maps, new_dev_maps);
 
 	/* Cleanup old maps */
-	if (dev_maps) {
-		for_each_possible_cpu(cpu) {
-			new_map = xmap_dereference(new_dev_maps->cpu_map[cpu]);
-			map = xmap_dereference(dev_maps->cpu_map[cpu]);
+	if (!dev_maps)
+		goto out_no_old_maps;
+
+	for_each_possible_cpu(cpu) {
+		tci = cpu * num_tc;
+		for (i = 0; i < num_tc; i++, tci++) {
+			new_map = xmap_dereference(new_dev_maps->cpu_map[tci]);
+			map = xmap_dereference(dev_maps->cpu_map[tci]);
 			if (map && map != new_map)
 				kfree_rcu(map, rcu);
 		}
-
-		kfree_rcu(dev_maps, rcu);
 	}
 
+	kfree_rcu(dev_maps, rcu);
+
+out_no_old_maps:
 	dev_maps = new_dev_maps;
 	active = true;
 
@@ -2162,11 +2212,13 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 
 	/* removes queue from unused CPUs */
 	for_each_possible_cpu(cpu) {
-		if (cpumask_test_cpu(cpu, mask) && cpu_online(cpu))
-			continue;
-
-		if (remove_xps_queue(dev_maps, cpu, index))
-			active = true;
+		tci = cpu * num_tc;
+		for (i = 0; i < tc; i++, tci++)
+			active |= remove_xps_queue(dev_maps, tci, index);
+		if (!cpumask_test_cpu(cpu, mask) || !cpu_online(cpu))
+			active |= remove_xps_queue(dev_maps, tci, index);
+		for (i = tc, tci++; ++i < num_tc; tci++)
+			active |= remove_xps_queue(dev_maps, tci, index);
 	}
 
 	/* free map if not active */
@@ -2182,11 +2234,15 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 error:
 	/* remove any maps that we added */
 	for_each_possible_cpu(cpu) {
-		new_map = xmap_dereference(new_dev_maps->cpu_map[cpu]);
-		map = dev_maps ? xmap_dereference(dev_maps->cpu_map[cpu]) :
-				 NULL;
-		if (new_map && new_map != map)
-			kfree(new_map);
+		tci = cpu * num_tc;
+		for (i = 0; i < num_tc; i++, tci++) {
+			new_map = xmap_dereference(new_dev_maps->cpu_map[tci]);
+			map = dev_maps ?
+			      xmap_dereference(dev_maps->cpu_map[tci]) :
+			      NULL;
+			if (new_map && new_map != map)
+				kfree(new_map);
+		}
 	}
 
 	mutex_unlock(&xps_map_mutex);
@@ -3146,8 +3202,14 @@ static inline int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
 	rcu_read_lock();
 	dev_maps = rcu_dereference(dev->xps_maps);
 	if (dev_maps) {
-		map = rcu_dereference(
-		    dev_maps->cpu_map[skb->sender_cpu - 1]);
+		unsigned int tci = skb->sender_cpu - 1;
+
+		if (dev->num_tc) {
+			tci *= dev->num_tc;
+			tci += netdev_get_prio_tc_map(dev, skb->priority);
+		}
+
+		map = rcu_dereference(dev_maps->cpu_map[tci]);
 		if (map) {
 			if (map->len == 1)
 				queue_index = map->queues[0];
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 6e4f347..763c1e1 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1190,29 +1190,38 @@ static ssize_t show_xps_map(struct netdev_queue *queue,
 			    struct netdev_queue_attribute *attribute, char *buf)
 {
 	struct net_device *dev = queue->dev;
+	int cpu, len, num_tc = 1, tc = 0;
 	struct xps_dev_maps *dev_maps;
 	cpumask_var_t mask;
 	unsigned long index;
-	int i, len;
 
 	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
 		return -ENOMEM;
 
 	index = get_netdev_queue_index(queue);
 
+	if (dev->num_tc) {
+		num_tc = dev->num_tc;
+		tc = netdev_txq_to_tc(dev, index);
+		if (tc < 0)
+			return -EINVAL;
+	}
+
 	rcu_read_lock();
 	dev_maps = rcu_dereference(dev->xps_maps);
 	if (dev_maps) {
-		for_each_possible_cpu(i) {
-			struct xps_map *map =
-			    rcu_dereference(dev_maps->cpu_map[i]);
-			if (map) {
-				int j;
-				for (j = 0; j < map->len; j++) {
-					if (map->queues[j] == index) {
-						cpumask_set_cpu(i, mask);
-						break;
-					}
+		for_each_possible_cpu(cpu) {
+			int i, tci = cpu * num_tc + tc;
+			struct xps_map *map;
+
+			map = rcu_dereference(dev_maps->cpu_map[tci]);
+			if (!map)
+				continue;
+
+			for (i = map->len; i--;) {
+				if (map->queues[i] == index) {
+					cpumask_set_cpu(cpu, mask);
+					break;
 				}
 			}
 		}

Re: [net-next PATCH 2/3] net: Refactor removal of queues from XPS map and apply on num_tc changes

From: Tom Herbert <hidden>
Date: 2016-10-28 02:35:15 

On Thu, Oct 27, 2016 at 8:40 AM, Alexander Duyck
[off-list ref] wrote:
quoted hunk
This patch updates the code for removing queues from the XPS map and makes
it so that we can apply the code any time we change either the number of
traffic classes or the mapping of a given block of queues.  This way we
avoid having queues pulling traffic from a foreign traffic class.

Signed-off-by: Alexander Duyck <redacted>
---
 net/core/dev.c |   79 ++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 56 insertions(+), 23 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index d4d45bf..d124081 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1953,32 +1953,56 @@ static void netif_setup_tc(struct net_device *dev, unsigned int txq)
 #define xmap_dereference(P)            \
        rcu_dereference_protected((P), lockdep_is_held(&xps_map_mutex))

-static struct xps_map *remove_xps_queue(struct xps_dev_maps *dev_maps,
-                                       int cpu, u16 index)
+static bool remove_xps_queue(struct xps_dev_maps *dev_maps,
+                            int tci, u16 index)
 {
        struct xps_map *map = NULL;
        int pos;

        if (dev_maps)
-               map = xmap_dereference(dev_maps->cpu_map[cpu]);
+               map = xmap_dereference(dev_maps->cpu_map[tci]);
+       if (!map)
+               return false;

-       for (pos = 0; map && pos < map->len; pos++) {
-               if (map->queues[pos] == index) {
-                       if (map->len > 1) {
-                               map->queues[pos] = map->queues[--map->len];
-                       } else {
-                               RCU_INIT_POINTER(dev_maps->cpu_map[cpu], NULL);
-                               kfree_rcu(map, rcu);
-                               map = NULL;
-                       }
+       for (pos = map->len; pos--;) {
+               if (map->queues[pos] != index)
+                       continue;
+
+               if (map->len > 1) {
+                       map->queues[pos] = map->queues[--map->len];
                        break;
                }
+
+               RCU_INIT_POINTER(dev_maps->cpu_map[tci], NULL);
+               kfree_rcu(map, rcu);
+               return false;
        }

-       return map;
+       return true;
 }

-static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
+static bool remove_xps_queue_cpu(struct net_device *dev,
+                                struct xps_dev_maps *dev_maps,
+                                int cpu, u16 offset, u16 count)
+{
+       bool active = false;
+       int i;
+
+       count += offset;
+       i = count;
+
+       do {
+               if (i-- == offset) {
+                       active = true;
+                       break;
+               }
+       } while (remove_xps_queue(dev_maps, cpu, i));
+
IMO do/while's are hard to read. Does something like this work:

static bool remove_xps_queue_cpu(struct net_device *dev,
                                struct xps_dev_maps *dev_maps,
                                int cpu, u16 offset, u16 count)
{
     int i;

     for (i = count + offset; i > offset; i--)
          if (!remove_xps_queue(dev_maps, cpu, i - 1))
              break;

     return (i == offset);
}
quoted hunk
+       return active;
+}
+
+static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
+                                  u16 count)
 {
        struct xps_dev_maps *dev_maps;
        int cpu, i;
@@ -1990,21 +2014,16 @@ static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
        if (!dev_maps)
                goto out_no_maps;

-       for_each_possible_cpu(cpu) {
-               for (i = index; i < dev->num_tx_queues; i++) {
-                       if (!remove_xps_queue(dev_maps, cpu, i))
-                               break;
-               }
-               if (i == dev->num_tx_queues)
-                       active = true;
-       }
+       for_each_possible_cpu(cpu)
+               active |= remove_xps_queue_cpu(dev, dev_maps, cpu, offset,
+                                              count);
Maybe just do dumb "if (remove_xps...) active = true;"
quoted hunk
        if (!active) {
                RCU_INIT_POINTER(dev->xps_maps, NULL);
                kfree_rcu(dev_maps, rcu);
        }

-       for (i = index; i < dev->num_tx_queues; i++)
+       for (i = offset + (count - 1); count--; i--)
                netdev_queue_numa_node_write(netdev_get_tx_queue(dev, i),
                                             NUMA_NO_NODE);

@@ -2012,6 +2031,11 @@ static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
        mutex_unlock(&xps_map_mutex);
 }

+static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
+{
+       netif_reset_xps_queues(dev, index, dev->num_tx_queues - index);
+}
+
 static struct xps_map *expand_xps_map(struct xps_map *map,
                                      int cpu, u16 index)
 {
@@ -2175,6 +2199,9 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 #endif
 void netdev_reset_tc(struct net_device *dev)
 {
+#ifdef CONFIG_XPS
+       netif_reset_xps_queues_gt(dev, 0);
+#endif
        dev->num_tc = 0;
        memset(dev->tc_to_txq, 0, sizeof(dev->tc_to_txq));
        memset(dev->prio_tc_map, 0, sizeof(dev->prio_tc_map));
@@ -2186,6 +2213,9 @@ int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset)
        if (tc >= dev->num_tc)
                return -EINVAL;

+#ifdef CONFIG_XPS
+       netif_reset_xps_queues(dev, offset, count);
+#endif
        dev->tc_to_txq[tc].count = count;
        dev->tc_to_txq[tc].offset = offset;
        return 0;
@@ -2197,6 +2227,9 @@ int netdev_set_num_tc(struct net_device *dev, u8 num_tc)
        if (num_tc > TC_MAX_QUEUE)
                return -EINVAL;

+#ifdef CONFIG_XPS
+       netif_reset_xps_queues_gt(dev, 0);
+#endif
        dev->num_tc = num_tc;
        return 0;
 }

Re: [net-next PATCH 3/3] net: Add support for XPS with QoS via traffic classes

From: Tom Herbert <hidden>
Date: 2016-10-28 02:38:29 

On Thu, Oct 27, 2016 at 8:40 AM, Alexander Duyck
[off-list ref] wrote:
This patch adds support for setting and using XPS when QoS via traffic
classes is enabled.  With this change we will factor in the priority and
traffic class mapping of the packet and use that information to correctly
select the queue.

This allows us to define a set of queues for a given traffic class via
mqprio and then configure the XPS mapping for those queues so that the
traffic flows can avoid head-of-line blocking between the individual CPUs
if so desired.
Does this change the sys API for XPS? Is it up the user to know which
are priority queues in sys?

Thanks,
Tom
quoted hunk
Signed-off-by: Alexander Duyck <redacted>
---
 include/linux/netdevice.h |    5 +-
 net/core/dev.c            |  136 +++++++++++++++++++++++++++++++++------------
 net/core/net-sysfs.c      |   31 +++++++---
 3 files changed, 122 insertions(+), 50 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d045432..56f90f7 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -732,8 +732,8 @@ struct xps_dev_maps {
        struct rcu_head rcu;
        struct xps_map __rcu *cpu_map[0];
 };
-#define XPS_DEV_MAPS_SIZE (sizeof(struct xps_dev_maps) +               \
-    (nr_cpu_ids * sizeof(struct xps_map *)))
+#define XPS_DEV_MAPS_SIZE(_tcs) (sizeof(struct xps_dev_maps) +         \
+       (nr_cpu_ids * (_tcs) * sizeof(struct xps_map *)))
 #endif /* CONFIG_XPS */

 #define TC_MAX_QUEUE   16
@@ -1920,6 +1920,7 @@ int netdev_set_prio_tc_map(struct net_device *dev, u8 prio, u8 tc)
        return 0;
 }

+int netdev_txq_to_tc(struct net_device *dev, unsigned int txq);
 void netdev_reset_tc(struct net_device *dev);
 int netdev_set_tc_queue(struct net_device *dev, u8 tc, u16 count, u16 offset);
 int netdev_set_num_tc(struct net_device *dev, u8 num_tc);
diff --git a/net/core/dev.c b/net/core/dev.c
index d124081..37c1096 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1948,6 +1948,23 @@ static void netif_setup_tc(struct net_device *dev, unsigned int txq)
        }
 }

+int netdev_txq_to_tc(struct net_device *dev, unsigned int txq)
+{
+       if (dev->num_tc) {
+               struct netdev_tc_txq *tc = &dev->tc_to_txq[0];
+               int i;
+
+               for (i = 0; i < TC_MAX_QUEUE; i++, tc++) {
+                       if ((txq - tc->offset) < tc->count)
+                               return i;
+               }
+
+               return -1;
+       }
+
+       return 0;
+}
+
 #ifdef CONFIG_XPS
 static DEFINE_MUTEX(xps_map_mutex);
 #define xmap_dereference(P)            \
@@ -1985,18 +2002,22 @@ static bool remove_xps_queue_cpu(struct net_device *dev,
                                 struct xps_dev_maps *dev_maps,
                                 int cpu, u16 offset, u16 count)
 {
+       int tc = dev->num_tc ? : 1;
        bool active = false;
-       int i;
+       int tci;

        count += offset;
-       i = count;

-       do {
-               if (i-- == offset) {
-                       active = true;
-                       break;
-               }
-       } while (remove_xps_queue(dev_maps, cpu, i));
+       for (tci = cpu * tc; tc--; tci++) {
+               int i = count;
+
+               do {
+                       if (i-- == offset) {
+                               active = true;
+                               break;
+                       }
+               } while (remove_xps_queue(dev_maps, tci, i));
+       }

        return active;
 }
@@ -2075,20 +2096,28 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
                        u16 index)
 {
        struct xps_dev_maps *dev_maps, *new_dev_maps = NULL;
+       int i, cpu, tci, numa_node_id = -2;
+       int maps_sz, num_tc = 1, tc = 0;
        struct xps_map *map, *new_map;
-       int maps_sz = max_t(unsigned int, XPS_DEV_MAPS_SIZE, L1_CACHE_BYTES);
-       int cpu, numa_node_id = -2;
        bool active = false;

+       if (dev->num_tc) {
+               num_tc = dev->num_tc;
+               tc = netdev_txq_to_tc(dev, index);
+               if (tc < 0)
+                       return -EINVAL;
+       }
+
+       maps_sz = XPS_DEV_MAPS_SIZE(num_tc);
+       if (maps_sz < L1_CACHE_BYTES)
+               maps_sz = L1_CACHE_BYTES;
+
        mutex_lock(&xps_map_mutex);

        dev_maps = xmap_dereference(dev->xps_maps);

        /* allocate memory for queue storage */
-       for_each_online_cpu(cpu) {
-               if (!cpumask_test_cpu(cpu, mask))
-                       continue;
-
+       for_each_cpu_and(cpu, cpu_online_mask, mask) {
                if (!new_dev_maps)
                        new_dev_maps = kzalloc(maps_sz, GFP_KERNEL);
                if (!new_dev_maps) {
@@ -2096,25 +2125,35 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
                        return -ENOMEM;
                }

-               map = dev_maps ? xmap_dereference(dev_maps->cpu_map[cpu]) :
+               tci = cpu * num_tc + tc;
+               map = dev_maps ? xmap_dereference(dev_maps->cpu_map[tci]) :
                                 NULL;

                map = expand_xps_map(map, cpu, index);
                if (!map)
                        goto error;

-               RCU_INIT_POINTER(new_dev_maps->cpu_map[cpu], map);
+               RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
        }

        if (!new_dev_maps)
                goto out_no_new_maps;

        for_each_possible_cpu(cpu) {
+               /* copy maps belonging to foreign traffic classes */
+               tci = cpu * num_tc;
+               for (i = 0; dev_maps && i < tc; i++, tci++) {
+                       /* fill in the new device map from the old device map */
+                       map = xmap_dereference(dev_maps->cpu_map[tci]);
+                       RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
+               }
+
+               tci = cpu * num_tc + tc;
                if (cpumask_test_cpu(cpu, mask) && cpu_online(cpu)) {
                        /* add queue to CPU maps */
                        int pos = 0;

-                       map = xmap_dereference(new_dev_maps->cpu_map[cpu]);
+                       map = xmap_dereference(new_dev_maps->cpu_map[tci]);
                        while ((pos < map->len) && (map->queues[pos] != index))
                                pos++;

@@ -2128,26 +2167,37 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 #endif
                } else if (dev_maps) {
                        /* fill in the new device map from the old device map */
-                       map = xmap_dereference(dev_maps->cpu_map[cpu]);
-                       RCU_INIT_POINTER(new_dev_maps->cpu_map[cpu], map);
+                       map = xmap_dereference(dev_maps->cpu_map[tci]);
+                       RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
                }

+               /* copy maps belonging to foreign traffic classes */
+               for (i = tc, tci++; dev_maps && (++i < num_tc); tci++) {
+                       /* fill in the new device map from the old device map */
+                       map = xmap_dereference(dev_maps->cpu_map[tci]);
+                       RCU_INIT_POINTER(new_dev_maps->cpu_map[tci], map);
+               }
        }

        rcu_assign_pointer(dev->xps_maps, new_dev_maps);

        /* Cleanup old maps */
-       if (dev_maps) {
-               for_each_possible_cpu(cpu) {
-                       new_map = xmap_dereference(new_dev_maps->cpu_map[cpu]);
-                       map = xmap_dereference(dev_maps->cpu_map[cpu]);
+       if (!dev_maps)
+               goto out_no_old_maps;
+
+       for_each_possible_cpu(cpu) {
+               tci = cpu * num_tc;
+               for (i = 0; i < num_tc; i++, tci++) {
+                       new_map = xmap_dereference(new_dev_maps->cpu_map[tci]);
+                       map = xmap_dereference(dev_maps->cpu_map[tci]);
                        if (map && map != new_map)
                                kfree_rcu(map, rcu);
                }
-
-               kfree_rcu(dev_maps, rcu);
        }

+       kfree_rcu(dev_maps, rcu);
+
+out_no_old_maps:
        dev_maps = new_dev_maps;
        active = true;

@@ -2162,11 +2212,13 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,

        /* removes queue from unused CPUs */
        for_each_possible_cpu(cpu) {
-               if (cpumask_test_cpu(cpu, mask) && cpu_online(cpu))
-                       continue;
-
-               if (remove_xps_queue(dev_maps, cpu, index))
-                       active = true;
+               tci = cpu * num_tc;
+               for (i = 0; i < tc; i++, tci++)
+                       active |= remove_xps_queue(dev_maps, tci, index);
+               if (!cpumask_test_cpu(cpu, mask) || !cpu_online(cpu))
+                       active |= remove_xps_queue(dev_maps, tci, index);
+               for (i = tc, tci++; ++i < num_tc; tci++)
+                       active |= remove_xps_queue(dev_maps, tci, index);
        }

        /* free map if not active */
@@ -2182,11 +2234,15 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
 error:
        /* remove any maps that we added */
        for_each_possible_cpu(cpu) {
-               new_map = xmap_dereference(new_dev_maps->cpu_map[cpu]);
-               map = dev_maps ? xmap_dereference(dev_maps->cpu_map[cpu]) :
-                                NULL;
-               if (new_map && new_map != map)
-                       kfree(new_map);
+               tci = cpu * num_tc;
+               for (i = 0; i < num_tc; i++, tci++) {
+                       new_map = xmap_dereference(new_dev_maps->cpu_map[tci]);
+                       map = dev_maps ?
+                             xmap_dereference(dev_maps->cpu_map[tci]) :
+                             NULL;
+                       if (new_map && new_map != map)
+                               kfree(new_map);
+               }
        }

        mutex_unlock(&xps_map_mutex);
@@ -3146,8 +3202,14 @@ static inline int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
        rcu_read_lock();
        dev_maps = rcu_dereference(dev->xps_maps);
        if (dev_maps) {
-               map = rcu_dereference(
-                   dev_maps->cpu_map[skb->sender_cpu - 1]);
+               unsigned int tci = skb->sender_cpu - 1;
+
+               if (dev->num_tc) {
+                       tci *= dev->num_tc;
+                       tci += netdev_get_prio_tc_map(dev, skb->priority);
+               }
+
+               map = rcu_dereference(dev_maps->cpu_map[tci]);
                if (map) {
                        if (map->len == 1)
                                queue_index = map->queues[0];
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 6e4f347..763c1e1 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1190,29 +1190,38 @@ static ssize_t show_xps_map(struct netdev_queue *queue,
                            struct netdev_queue_attribute *attribute, char *buf)
 {
        struct net_device *dev = queue->dev;
+       int cpu, len, num_tc = 1, tc = 0;
        struct xps_dev_maps *dev_maps;
        cpumask_var_t mask;
        unsigned long index;
-       int i, len;

        if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
                return -ENOMEM;

        index = get_netdev_queue_index(queue);

+       if (dev->num_tc) {
+               num_tc = dev->num_tc;
+               tc = netdev_txq_to_tc(dev, index);
+               if (tc < 0)
+                       return -EINVAL;
+       }
+
        rcu_read_lock();
        dev_maps = rcu_dereference(dev->xps_maps);
        if (dev_maps) {
-               for_each_possible_cpu(i) {
-                       struct xps_map *map =
-                           rcu_dereference(dev_maps->cpu_map[i]);
-                       if (map) {
-                               int j;
-                               for (j = 0; j < map->len; j++) {
-                                       if (map->queues[j] == index) {
-                                               cpumask_set_cpu(i, mask);
-                                               break;
-                                       }
+               for_each_possible_cpu(cpu) {
+                       int i, tci = cpu * num_tc + tc;
+                       struct xps_map *map;
+
+                       map = rcu_dereference(dev_maps->cpu_map[tci]);
+                       if (!map)
+                               continue;
+
+                       for (i = map->len; i--;) {
+                               if (map->queues[i] == index) {
+                                       cpumask_set_cpu(cpu, mask);
+                                       break;
                                }
                        }
                }

Re: [Intel-wired-lan] [net-next PATCH 2/3] net: Refactor removal of queues from XPS map and apply on num_tc changes

From: Alexander Duyck <hidden>
Date: 2016-10-28 14:54:08 

On Thu, Oct 27, 2016 at 7:35 PM, Tom Herbert [off-list ref] wrote:
On Thu, Oct 27, 2016 at 8:40 AM, Alexander Duyck
[off-list ref] wrote:
quoted
This patch updates the code for removing queues from the XPS map and makes
it so that we can apply the code any time we change either the number of
traffic classes or the mapping of a given block of queues.  This way we
avoid having queues pulling traffic from a foreign traffic class.

Signed-off-by: Alexander Duyck <redacted>
---
 net/core/dev.c |   79 ++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 56 insertions(+), 23 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index d4d45bf..d124081 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1953,32 +1953,56 @@ static void netif_setup_tc(struct net_device *dev, unsigned int txq)
 #define xmap_dereference(P)            \
        rcu_dereference_protected((P), lockdep_is_held(&xps_map_mutex))

-static struct xps_map *remove_xps_queue(struct xps_dev_maps *dev_maps,
-                                       int cpu, u16 index)
+static bool remove_xps_queue(struct xps_dev_maps *dev_maps,
+                            int tci, u16 index)
 {
        struct xps_map *map = NULL;
        int pos;

        if (dev_maps)
-               map = xmap_dereference(dev_maps->cpu_map[cpu]);
+               map = xmap_dereference(dev_maps->cpu_map[tci]);
+       if (!map)
+               return false;

-       for (pos = 0; map && pos < map->len; pos++) {
-               if (map->queues[pos] == index) {
-                       if (map->len > 1) {
-                               map->queues[pos] = map->queues[--map->len];
-                       } else {
-                               RCU_INIT_POINTER(dev_maps->cpu_map[cpu], NULL);
-                               kfree_rcu(map, rcu);
-                               map = NULL;
-                       }
+       for (pos = map->len; pos--;) {
+               if (map->queues[pos] != index)
+                       continue;
+
+               if (map->len > 1) {
+                       map->queues[pos] = map->queues[--map->len];
                        break;
                }
+
+               RCU_INIT_POINTER(dev_maps->cpu_map[tci], NULL);
+               kfree_rcu(map, rcu);
+               return false;
        }

-       return map;
+       return true;
 }

-static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
+static bool remove_xps_queue_cpu(struct net_device *dev,
+                                struct xps_dev_maps *dev_maps,
+                                int cpu, u16 offset, u16 count)
+{
+       bool active = false;
+       int i;
+
+       count += offset;
+       i = count;
+
+       do {
+               if (i-- == offset) {
+                       active = true;
+                       break;
+               }
+       } while (remove_xps_queue(dev_maps, cpu, i));
+
IMO do/while's are hard to read. Does something like this work:

static bool remove_xps_queue_cpu(struct net_device *dev,
                                struct xps_dev_maps *dev_maps,
                                int cpu, u16 offset, u16 count)
{
     int i;

     for (i = count + offset; i > offset; i--)
          if (!remove_xps_queue(dev_maps, cpu, i - 1))
              break;

     return (i == offset);
}
I can flip the do/while back to a for loop.  That shouldn't be too big
of a deal, although I might see if I could convert the loop to do a
pre-decrement instead of a post-decrement.  Then I could just check
for (i - offset) < 0.
quoted
+       return active;
+}
+
+static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
+                                  u16 count)
 {
        struct xps_dev_maps *dev_maps;
        int cpu, i;
@@ -1990,21 +2014,16 @@ static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
        if (!dev_maps)
                goto out_no_maps;

-       for_each_possible_cpu(cpu) {
-               for (i = index; i < dev->num_tx_queues; i++) {
-                       if (!remove_xps_queue(dev_maps, cpu, i))
-                               break;
-               }
-               if (i == dev->num_tx_queues)
-                       active = true;
-       }
+       for_each_possible_cpu(cpu)
+               active |= remove_xps_queue_cpu(dev, dev_maps, cpu, offset,
+                                              count);
Maybe just do dumb "if (remove_xps...) active = true;"
I prefer the |= for a loop where the initial value is false and we are
looping and setting it to true on a given condition, especially when
the given condition is a Boolean value.  It results in faster and
smaller code using the |= since it is literally just an OR operation
instead of having to do a TEST/JMP/MOV combination.

Re: [Intel-wired-lan] [net-next PATCH 3/3] net: Add support for XPS with QoS via traffic classes

From: Alexander Duyck <hidden>
Date: 2016-10-28 14:58:54 

On Thu, Oct 27, 2016 at 7:38 PM, Tom Herbert [off-list ref] wrote:
On Thu, Oct 27, 2016 at 8:40 AM, Alexander Duyck
[off-list ref] wrote:
quoted
This patch adds support for setting and using XPS when QoS via traffic
classes is enabled.  With this change we will factor in the priority and
traffic class mapping of the packet and use that information to correctly
select the queue.

This allows us to define a set of queues for a given traffic class via
mqprio and then configure the XPS mapping for those queues so that the
traffic flows can avoid head-of-line blocking between the individual CPUs
if so desired.
Does this change the sys API for XPS? Is it up the user to know which
are priority queues in sys?
The idea was to keep the change transparent.  So for now the only
change in relation to XPS from the XPS point of view is that the map
for a given queue is invalidated when either the dev->num_tcs changes
or if the queue is moved into a dev->tx_to_txq mapping.  Otherwise the
interface should behave exactly the same as before.

One thing I could look at doing is adding a read-only sysfs value that
the user could use to identify which traffic class a given queue
belongs to.  Then at least that way they would be able to dump both
the XPS map and the tc to determine how the traffic will flow through
the device.

Thanks.

- Alex

Re: [Intel-wired-lan] [net-next PATCH 3/3] net: Add support for XPS with QoS via traffic classes

From: John Fastabend <john.fastabend@gmail.com>
Date: 2016-10-28 15:49:52 

On 16-10-28 07:58 AM, Alexander Duyck wrote:
On Thu, Oct 27, 2016 at 7:38 PM, Tom Herbert [off-list ref] wrote:
quoted
On Thu, Oct 27, 2016 at 8:40 AM, Alexander Duyck
[off-list ref] wrote:
quoted
This patch adds support for setting and using XPS when QoS via traffic
classes is enabled.  With this change we will factor in the priority and
traffic class mapping of the packet and use that information to correctly
select the queue.

This allows us to define a set of queues for a given traffic class via
mqprio and then configure the XPS mapping for those queues so that the
traffic flows can avoid head-of-line blocking between the individual CPUs
if so desired.
Does this change the sys API for XPS? Is it up the user to know which
are priority queues in sys?
The idea was to keep the change transparent.  So for now the only
change in relation to XPS from the XPS point of view is that the map
for a given queue is invalidated when either the dev->num_tcs changes
or if the queue is moved into a dev->tx_to_txq mapping.  Otherwise the
interface should behave exactly the same as before.

One thing I could look at doing is adding a read-only sysfs value that
the user could use to identify which traffic class a given queue
belongs to.  Then at least that way they would be able to dump both
the XPS map and the tc to determine how the traffic will flow through
the device.
I could see some value in a sysfs read-only tc-queue mapping might be
especially for devices that are negotiating these things using firmware.

.John
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