Date:	Sun, 22 Aug 2010 22:39:57 -0700 (PDT)
From:	Tom Herbert <therbert@...gle.com>
To:	davem@...emloft.net, netdev@...r.kernel.org
cc:	eric.dumazet@...il.com
Subject: [PATCH] xps-mq: Transmit Packet Steering for multiqueue

This patch implements transmit packet steering (XPS) for multiqueue
devices.  XPS selects a transmit queue during packet transmission based
on configuration.  This is done by mapping the CPU transmitting the
packet to a queue.  This is the transmit side analogue to RPS-- where
RPS is selecting a CPU based on receive queue, XPS selects a queue
based on the CPU (previously there was an XPS patch from Eric
Dumazet, but that might more appropriately be called transmit completion
steering).

Each transmit queue can be associated with a number of CPUs which will
used the queue to send packets.  This is configured as a CPU mask on a
per queue basis in:

/sys/class/net/eth<n>/queues/tx-<n>/xps_cpus

The mappings are stored per device in an inverted data structure that
maps CPUs to queues.  In the netdevice structure this is an array of
num_possible_cpu structures where each array entry contains a bit map
of queues which that CPU can use.

We also allow the mapping of a socket to queue to be modified, for
instance if a thread is scheduled on a different CPU the desired queue
for transmitting packets would likely change.  To maintain in order
packet transmission a flag (ooo_okay) has been added to the sk_buf
structure.  If a transport layer sets this flag on a packet, the
transmit queue can be changed for this socket.  Presumably, the
transport would set this is there was no possbility of creating ooo
packets (for instance there are no packets in flight for the socket).
This patch includes the modification in TCP output for setting this
flag.

The benefits of XPS are improved locality in the per queue data
strutures.  Also, transmit completions are more likely to be done
nearer to the sending thread so this should promote locality back 
to the socket (e.g. UDP).  The benefits of XPS are dependent on
cache hierarchy, application load, and other factors.  XPS would
nominally be configured so that a queue would only be shared by CPUs
which are sharing a cache, the degenerative configuration woud be that
each CPU has it's own queue.

Below are some benchmark results which show the potential benfit of
this patch.  The netperf test has 500 instances of netperf TCP_RR test
with 1 byte req. and resp.

bnx2x on 16 core AMD
   XPS (16 queues, 1 TX queue per CPU)	1015K at 99% CPU
   No XPS (16 queues)			1127K at 98% CPU

Signed-off-by: Tom Herbert <therbert@...gle.com>
---
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 46c36ff..0ff6c9f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -497,6 +497,12 @@ struct netdev_queue {
 	struct Qdisc		*qdisc;
 	unsigned long		state;
 	struct Qdisc		*qdisc_sleeping;
+#ifdef CONFIG_RPS
+	struct kobject		kobj;
+	struct netdev_queue	*first;
+	atomic_t		count;
+#endif
+
 /*
  * write mostly part
  */
@@ -524,6 +530,22 @@ struct rps_map {
 #define RPS_MAP_SIZE(_num) (sizeof(struct rps_map) + (_num * sizeof(u16)))
 
 /*
+ * This structure holds an XPS map which can be of variable length.  queues
+ * is an array of num_possible_cpus entries, where each entry is a mask of
+ * queues for that CPU (up to num_tx_queues bits for device).
+ */
+struct xps_map {
+	struct rcu_head rcu;
+	unsigned long queues[0];
+};
+
+#define QUEUE_MASK_SIZE(dev) (BITS_TO_LONGS(dev->num_tx_queues))
+#define XPS_MAP_SIZE(dev) (sizeof(struct xps_map) + (num_possible_cpus() * \
+    QUEUE_MASK_SIZE(dev) * sizeof(unsigned long)))
+#define XPS_ENTRY(map, offset, dev) \
+    (&map->queues[offset * QUEUE_MASK_SIZE(dev)])
+
+/*
  * The rps_dev_flow structure contains the mapping of a flow to a CPU and the
  * tail pointer for that CPU's input queue at the time of last enqueue.
  */
@@ -978,6 +1000,9 @@ struct net_device {
 	void			*rx_handler_data;
 
 	struct netdev_queue	*_tx ____cacheline_aligned_in_smp;
+#ifdef CONFIG_RPS
+	struct xps_map		*xps_maps;
+#endif
 
 	/* Number of TX queues allocated at alloc_netdev_mq() time  */
 	unsigned int		num_tx_queues;
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f067c95..146df6f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -381,6 +381,7 @@ struct sk_buff {
 #else
 	__u8			deliver_no_wcard:1;
 #endif
+	__u8			ooo_okay:1;
 	kmemcheck_bitfield_end(flags2);
 
 	/* 0/14 bit hole */
diff --git a/net/core/dev.c b/net/core/dev.c
index da584f5..d23f9c4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2054,6 +2054,60 @@ static inline u16 dev_cap_txqueue(struct net_device *dev, u16 queue_index)
 	return queue_index;
 }
 
+static inline int get_xps_queue(struct net_device *dev, struct sk_buff *skb,
+				int queue_index)
+{
+	struct xps_map *maps;
+	int cpu = smp_processor_id();
+	u32 hash;
+	unsigned long *queues;
+	int weight, select;
+
+	rcu_read_lock();
+	maps = rcu_dereference(dev->xps_maps);
+
+	if (!maps) {
+		rcu_read_unlock();
+		return queue_index;
+	}
+
+	queues = XPS_ENTRY(maps, cpu, dev);
+
+	if (queue_index >= 0) {
+		if (test_bit(queue_index, queues)) {
+			rcu_read_unlock();
+			return queue_index;
+		}
+	}
+
+	weight = bitmap_weight(queues, dev->real_num_tx_queues);
+	switch (weight) {
+	case 0:
+		break;
+	case 1:
+		queue_index =
+		    find_first_bit(queues, dev->real_num_tx_queues);
+		break;
+	default:
+		if (skb->sk && skb->sk->sk_hash)
+			hash = skb->sk->sk_hash;
+		else
+			hash = (__force u16) skb->protocol ^ skb->rxhash;
+		hash = jhash_1word(hash, hashrnd);
+
+		select = ((u64) hash * weight) >> 32;
+		queue_index =
+		    find_first_bit(queues, dev->real_num_tx_queues);
+		while (select--)
+			queue_index = find_next_bit(queues,
+			    dev->real_num_tx_queues, queue_index);
+		break;
+	}
+
+	rcu_read_unlock();
+	return queue_index;
+}
+
 static struct netdev_queue *dev_pick_tx(struct net_device *dev,
 					struct sk_buff *skb)
 {
@@ -2061,23 +2115,30 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
 	struct sock *sk = skb->sk;
 
 	queue_index = sk_tx_queue_get(sk);
-	if (queue_index < 0) {
+
+	if (queue_index < 0 || (skb->ooo_okay && dev->real_num_tx_queues > 1)) {
 		const struct net_device_ops *ops = dev->netdev_ops;
+		int old_index = queue_index;
 
 		if (ops->ndo_select_queue) {
 			queue_index = ops->ndo_select_queue(dev, skb);
 			queue_index = dev_cap_txqueue(dev, queue_index);
 		} else {
-			queue_index = 0;
-			if (dev->real_num_tx_queues > 1)
-				queue_index = skb_tx_hash(dev, skb);
+			if (dev->real_num_tx_queues > 1) {
+				queue_index = get_xps_queue(dev,
+				    skb, queue_index);
+				if (queue_index < 0)
+					queue_index = skb_tx_hash(dev, skb);
+			} else
+				queue_index = 0;
+		}
 
-			if (sk) {
-				struct dst_entry *dst = rcu_dereference_check(sk->sk_dst_cache, 1);
+		if ((queue_index != old_index) && sk) {
+			struct dst_entry *dst =
+			    rcu_dereference_check(sk->sk_dst_cache, 1);
 
-				if (dst && skb_dst(skb) == dst)
-					sk_tx_queue_set(sk, queue_index);
-			}
+			if (dst && skb_dst(skb) == dst)
+				sk_tx_queue_set(sk, queue_index);
 		}
 	}
 
@@ -5429,6 +5490,15 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 	}
 
 #ifdef CONFIG_RPS
+	atomic_set(&tx->count, queue_count);
+
+	/*
+	 * Set a pointer to first element in the array which holds the
+	 * reference count.
+	 */
+	for (i = 0; i < queue_count; i++)
+		tx[i].first = tx;
+
 	rx = kcalloc(queue_count, sizeof(struct netdev_rx_queue), GFP_KERNEL);
 	if (!rx) {
 		printk(KERN_ERR "alloc_netdev: Unable to allocate "
@@ -5506,7 +5576,9 @@ void free_netdev(struct net_device *dev)
 
 	release_net(dev_net(dev));
 
+#ifndef CONFIG_RPS
 	kfree(dev->_tx);
+#endif
 
 	/* Flush device addresses */
 	dev_addr_flush(dev);
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index af4dfba..661c481 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -742,34 +742,295 @@ static int rx_queue_add_kobject(struct net_device *net, int index)
 	return error;
 }
 
-static int rx_queue_register_kobjects(struct net_device *net)
+/*
+ * netdev_queue sysfs structures and functions.
+ */
+struct netdev_queue_attribute {
+	struct attribute attr;
+	ssize_t (*show)(struct netdev_queue *queue,
+	    struct netdev_queue_attribute *attr, char *buf);
+	ssize_t (*store)(struct netdev_queue *queue,
+	    struct netdev_queue_attribute *attr, const char *buf, size_t len);
+};
+#define to_netdev_queue_attr(_attr) container_of(_attr,		\
+    struct netdev_queue_attribute, attr)
+
+#define to_netdev_queue(obj) container_of(obj, struct netdev_queue, kobj)
+
+static ssize_t netdev_queue_attr_show(struct kobject *kobj,
+				      struct attribute *attr, char *buf)
+{
+	struct netdev_queue_attribute *attribute = to_netdev_queue_attr(attr);
+	struct netdev_queue *queue = to_netdev_queue(kobj);
+
+	if (!attribute->show)
+		return -EIO;
+
+	return attribute->show(queue, attribute, buf);
+}
+
+static ssize_t netdev_queue_attr_store(struct kobject *kobj,
+				       struct attribute *attr,
+				       const char *buf, size_t count)
+{
+	struct netdev_queue_attribute *attribute = to_netdev_queue_attr(attr);
+	struct netdev_queue *queue = to_netdev_queue(kobj);
+
+	if (!attribute->store)
+		return -EIO;
+
+	return attribute->store(queue, attribute, buf, count);
+}
+
+static struct sysfs_ops netdev_queue_sysfs_ops = {
+	.show = netdev_queue_attr_show,
+	.store = netdev_queue_attr_store,
+};
+
+static inline unsigned int get_netdev_queue_index(struct netdev_queue *queue)
 {
+	struct net_device *dev = queue->dev;
+	int i;
+
+	for (i = 0; i < dev->num_tx_queues; i++)
+		if (queue == &dev->_tx[i])
+			break;
+
+	BUG_ON(i >= dev->num_tx_queues);
+
+	return i;
+}
+
+static ssize_t show_xps_map(struct netdev_queue *queue,
+			    struct netdev_queue_attribute *attribute, char *buf)
+{
+	struct net_device *dev = queue->dev;
+	struct xps_map *maps;
+	cpumask_var_t mask;
+	unsigned long *qmask, index;
+	size_t len = 0;
 	int i;
+	unsigned int qmask_size = QUEUE_MASK_SIZE(dev);
+
+	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
+		return -ENOMEM;
+
+	index = get_netdev_queue_index(queue);
+
+	rcu_read_lock();
+	maps = rcu_dereference(dev->xps_maps);
+	if (maps) {
+		qmask = maps->queues;
+		for (i = 0; i < num_possible_cpus(); i++) {
+			if (test_bit(index, qmask))
+				cpumask_set_cpu(i, mask);
+			qmask += qmask_size;
+		}
+	}
+	len += cpumask_scnprintf(buf + len, PAGE_SIZE, mask);
+	if (PAGE_SIZE - len < 3) {
+		rcu_read_unlock();
+		free_cpumask_var(mask);
+		return -EINVAL;
+	}
+	rcu_read_unlock();
+
+	free_cpumask_var(mask);
+	len += sprintf(buf + len, "\n");
+	return len;
+}
+
+static void xps_map_release(struct rcu_head *rcu)
+{
+	struct xps_map *map = container_of(rcu, struct xps_map, rcu);
+
+	kfree(map);
+}
+
+static DEFINE_MUTEX(xps_map_lock);
+
+static ssize_t store_xps_map(struct netdev_queue *queue,
+		      struct netdev_queue_attribute *attribute,
+		      const char *buf, size_t len)
+{
+	struct net_device *dev = queue->dev;
+	struct xps_map *maps;
+	cpumask_var_t mask;
+	int err, i, nonempty = 0;
+	unsigned long *qmask, index;
+	unsigned int qmask_size = QUEUE_MASK_SIZE(dev);
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+		return -ENOMEM;
+
+	err = bitmap_parse(buf, len, cpumask_bits(mask), nr_cpumask_bits);
+	if (err) {
+		free_cpumask_var(mask);
+		return err;
+	}
+
+	mutex_lock(&xps_map_lock);
+
+	maps = dev->xps_maps;
+	if (!maps) {
+		if (!cpumask_weight(mask)) {
+			mutex_unlock(&xps_map_lock);
+			free_cpumask_var(mask);
+			return 0;
+		}
+		maps = kzalloc(XPS_MAP_SIZE(dev), GFP_KERNEL);
+		if (!maps) {
+			mutex_unlock(&xps_map_lock);
+			free_cpumask_var(mask);
+			return -ENOMEM;
+		}
+		rcu_assign_pointer(dev->xps_maps, maps);
+	}
+
+	index = get_netdev_queue_index(queue);
+
+	qmask = maps->queues;
+	for (i = 0; i < num_possible_cpus(); i++) {
+		if (cpu_isset(i, *mask) && cpu_online(i)) {
+			set_bit(index, qmask);
+			nonempty = 1;
+		} else
+			clear_bit(index, qmask);
+		if (!nonempty &&
+		    bitmap_weight(qmask, dev->real_num_tx_queues))
+			nonempty = 1;
+		qmask += qmask_size;
+	}
+
+	if (!nonempty) {
+		rcu_assign_pointer(dev->xps_maps, NULL);
+		call_rcu(&maps->rcu, xps_map_release);
+	}
+
+	mutex_unlock(&xps_map_lock);
+
+	free_cpumask_var(mask);
+	return len;
+}
+
+static struct netdev_queue_attribute xps_cpus_attribute =
+    __ATTR(xps_cpus, S_IRUGO | S_IWUSR, show_xps_map, store_xps_map);
+
+static struct attribute *netdev_queue_default_attrs[] = {
+	&xps_cpus_attribute.attr,
+	NULL
+};
+
+static void netdev_queue_release(struct kobject *kobj)
+{
+	struct netdev_queue *queue = to_netdev_queue(kobj);
+	struct net_device *dev = queue->dev;
+	struct netdev_queue *first = queue->first;
+	struct xps_map *maps;
+	unsigned long *qmask, index;
+	int i, nonempty = 0;
+	unsigned int qmask_size = QUEUE_MASK_SIZE(dev);
+
+	index = get_netdev_queue_index(queue);
+
+	mutex_lock(&xps_map_lock);
+
+	maps = dev->xps_maps;
+
+	if (maps) {
+		qmask = maps->queues;
+		for (i = 0; i < num_possible_cpus(); i++) {
+			clear_bit(index, qmask);
+			if (!nonempty &&
+			    bitmap_weight(qmask, dev->real_num_tx_queues))
+				nonempty = 1;
+			qmask += qmask_size;
+		}
+
+		if (!nonempty) {
+			rcu_assign_pointer(dev->xps_maps, NULL);
+			call_rcu(&maps->rcu, xps_map_release);
+		}
+	}
+	mutex_unlock(&xps_map_lock);
+
+	if (atomic_dec_and_test(&first->count)) {
+		kfree(first);
+		dev_put(dev);
+	}
+}
+
+static struct kobj_type netdev_queue_ktype = {
+	.sysfs_ops = &netdev_queue_sysfs_ops,
+	.release = netdev_queue_release,
+	.default_attrs = netdev_queue_default_attrs,
+};
+
+static int netdev_queue_add_kobject(struct net_device *net, int index)
+{
+	struct netdev_queue *queue = net->_tx + index;
+	struct kobject *kobj = &queue->kobj;
+	int error = 0;
+
+	kobj->kset = net->queues_kset;
+	error = kobject_init_and_add(kobj, &netdev_queue_ktype, NULL,
+	    "tx-%u", index);
+	if (error) {
+		kobject_put(kobj);
+		return error;
+	}
+
+	kobject_uevent(kobj, KOBJ_ADD);
+
+	return error;
+}
+
+static int register_queue_kobjects(struct net_device *net)
+{
+	int rx = 0, tx = 0;
 	int error = 0;
 
 	net->queues_kset = kset_create_and_add("queues",
 	    NULL, &net->dev.kobj);
 	if (!net->queues_kset)
 		return -ENOMEM;
-	for (i = 0; i < net->num_rx_queues; i++) {
-		error = rx_queue_add_kobject(net, i);
+
+	for (rx = 0; rx < net->num_rx_queues; rx++) {
+		error = rx_queue_add_kobject(net, rx);
 		if (error)
-			break;
+			goto error;
 	}
 
-	if (error)
-		while (--i >= 0)
-			kobject_put(&net->_rx[i].kobj);
+	for (tx = 0; tx < net->num_tx_queues; tx++) {
+		error = netdev_queue_add_kobject(net, tx);
+		if (error)
+			goto error;
+	}
+	dev_hold(net);
+
+	return error;
+
+error:
+	while (--rx >= 0)
+		kobject_put(&net->_rx[rx].kobj);
+
+	while (--tx >= 0)
+		kobject_put(&net->_tx[tx].kobj);
 
 	return error;
 }
 
-static void rx_queue_remove_kobjects(struct net_device *net)
+static void remove_queue_kobjects(struct net_device *net)
 {
 	int i;
 
 	for (i = 0; i < net->num_rx_queues; i++)
 		kobject_put(&net->_rx[i].kobj);
+	for (i = 0; i < net->num_tx_queues; i++)
+		kobject_put(&net->_tx[i].kobj);
 	kset_unregister(net->queues_kset);
 }
 #endif /* CONFIG_RPS */
@@ -871,7 +1132,7 @@ void netdev_unregister_kobject(struct net_device * net)
 	kobject_get(&dev->kobj);
 
 #ifdef CONFIG_RPS
-	rx_queue_remove_kobjects(net);
+	remove_queue_kobjects(net);
 #endif
 
 	device_del(dev);
@@ -912,7 +1173,7 @@ int netdev_register_kobject(struct net_device *net)
 		return error;
 
 #ifdef CONFIG_RPS
-	error = rx_queue_register_kobjects(net);
+	error = register_queue_kobjects(net);
 	if (error) {
 		device_del(dev);
 		return error;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index de3bd84..80c1928 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -828,8 +828,10 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 							   &md5);
 	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
 
-	if (tcp_packets_in_flight(tp) == 0)
+	if (tcp_packets_in_flight(tp) == 0) {
 		tcp_ca_event(sk, CA_EVENT_TX_START);
+		skb->ooo_okay = 1;
+	}
 
 	skb_push(skb, tcp_header_size);
 	skb_reset_transport_header(skb);

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