tuntap: choose the txq based on rxq

This patch implements a simple multiqueue flow steering policy - tx follows rx
for tun/tap. The idea is simple, it just choose the txq based on which rxq it
comes. The flow were identified through the rxhash of a skb, and the hash to
queue mapping were recorded in a hlist with an ageing timer to retire the
mapping. The mapping were created when tun receives packet from userspace, and
was quired in .ndo_select_queue().

I run co-current TCP_CRR test and didn't see any mapping manipulation helpers in
perf top, so the overhead could be negelected.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 224 insertions, 3 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 79b6f9ecc12c..9e287680cd2e 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -115,6 +115,8 @@ struct tap_filter {
  */
 #define MAX_TAP_QUEUES 1024
 
+#define TUN_FLOW_EXPIRE (3 * HZ)
+
 /* A tun_file connects an open character device to a tuntap netdevice. It
  * also contains all socket related strctures (except sock_fprog and tap_filter)
  * to serve as one transmit queue for tuntap device. The sock_fprog and
@@ -138,6 +140,18 @@ struct tun_file {
         u16 queue_index;
 };
 
+struct tun_flow_entry {
+        struct hlist_node hash_link;
+        struct rcu_head rcu;
+        struct tun_struct *tun;
+
+        u32 rxhash;
+        int queue_index;
+        unsigned long updated;
+};
+
+#define TUN_NUM_FLOW_ENTRIES 1024
+
 /* Since the socket were moved to tun_file, to preserve the behavior of persist
  * device, socket fileter, sndbuf and vnet header size were restore when the
  * file were attached to a persist device.
@@ -163,8 +177,164 @@ struct tun_struct {
 #ifdef TUN_DEBUG
         int debug;
 #endif
+        spinlock_t lock;
+        struct kmem_cache *flow_cache;
+        struct hlist_head flows[TUN_NUM_FLOW_ENTRIES];
+        struct timer_list flow_gc_timer;
+        unsigned long ageing_time;
 };
 
+static inline u32 tun_hashfn(u32 rxhash)
+{
+        return rxhash & 0x3ff;
+}
+
+static struct tun_flow_entry *tun_flow_find(struct hlist_head *head, u32 rxhash)
+{
+        struct tun_flow_entry *e;
+        struct hlist_node *n;
+
+        hlist_for_each_entry_rcu(e, n, head, hash_link) {
+                if (e->rxhash == rxhash)
+                        return e;
+        }
+        return NULL;
+}
+
+static struct tun_flow_entry *tun_flow_create(struct tun_struct *tun,
+                                              struct hlist_head *head,
+                                              u32 rxhash, u16 queue_index)
+{
+        struct tun_flow_entry *e = kmem_cache_alloc(tun->flow_cache,
+                                                    GFP_ATOMIC);
+        if (e) {
+                tun_debug(KERN_INFO, tun, "create flow: hash %u index %u\n",
+                          rxhash, queue_index);
+                e->updated = jiffies;
+                e->rxhash = rxhash;
+                e->queue_index = queue_index;
+                e->tun = tun;
+                hlist_add_head_rcu(&e->hash_link, head);
+        }
+        return e;
+}
+
+static void tun_flow_free(struct rcu_head *head)
+{
+        struct tun_flow_entry *e
+                = container_of(head, struct tun_flow_entry, rcu);
+        kmem_cache_free(e->tun->flow_cache, e);
+}
+
+static void tun_flow_delete(struct tun_struct *tun, struct tun_flow_entry *e)
+{
+        tun_debug(KERN_INFO, tun, "delete flow: hash %u index %u\n",
+                  e->rxhash, e->queue_index);
+        hlist_del_rcu(&e->hash_link);
+        call_rcu(&e->rcu, tun_flow_free);
+}
+
+static void tun_flow_flush(struct tun_struct *tun)
+{
+        int i;
+
+        spin_lock_bh(&tun->lock);
+        for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
+                struct tun_flow_entry *e;
+                struct hlist_node *h, *n;
+
+                hlist_for_each_entry_safe(e, h, n, &tun->flows[i], hash_link)
+                        tun_flow_delete(tun, e);
+        }
+        spin_unlock_bh(&tun->lock);
+}
+
+static void tun_flow_delete_by_queue(struct tun_struct *tun, u16 queue_index)
+{
+        int i;
+
+        spin_lock_bh(&tun->lock);
+        for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
+                struct tun_flow_entry *e;
+                struct hlist_node *h, *n;
+
+                hlist_for_each_entry_safe(e, h, n, &tun->flows[i], hash_link) {
+                        if (e->queue_index == queue_index)
+                                tun_flow_delete(tun, e);
+                }
+        }
+        spin_unlock_bh(&tun->lock);
+}
+
+static void tun_flow_cleanup(unsigned long data)
+{
+        struct tun_struct *tun = (struct tun_struct *)data;
+        unsigned long delay = tun->ageing_time;
+        unsigned long next_timer = jiffies + delay;
+        unsigned long count = 0;
+        int i;
+
+        tun_debug(KERN_INFO, tun, "tun_flow_cleanup\n");
+
+        spin_lock_bh(&tun->lock);
+        for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
+                struct tun_flow_entry *e;
+                struct hlist_node *h, *n;
+
+                hlist_for_each_entry_safe(e, h, n, &tun->flows[i], hash_link) {
+                        unsigned long this_timer;
+                        count++;
+                        this_timer = e->updated + delay;
+                        if (time_before_eq(this_timer, jiffies))
+                                tun_flow_delete(tun, e);
+                        else if (time_before(this_timer, next_timer))
+                                next_timer = this_timer;
+                }
+        }
+
+        if (count)
+                mod_timer(&tun->flow_gc_timer, round_jiffies_up(next_timer));
+        spin_unlock_bh(&tun->lock);
+}
+
+static void tun_flow_update(struct tun_struct *tun, struct sk_buff *skb,
+                            u16 queue_index)
+{
+        struct hlist_head *head;
+        struct tun_flow_entry *e;
+        unsigned long delay = tun->ageing_time;
+        u32 rxhash = skb_get_rxhash(skb);
+
+        if (!rxhash)
+                return;
+        else
+                head = &tun->flows[tun_hashfn(rxhash)];
+
+        rcu_read_lock();
+
+        if (tun->numqueues == 1)
+                goto unlock;
+
+        e = tun_flow_find(head, rxhash);
+        if (likely(e)) {
+                /* TODO: keep queueing to old queue until it's empty? */
+                e->queue_index = queue_index;
+                e->updated = jiffies;
+        } else {
+                spin_lock_bh(&tun->lock);
+                if (!tun_flow_find(head, rxhash))
+                        tun_flow_create(tun, head, rxhash, queue_index);
+
+                if (!timer_pending(&tun->flow_gc_timer))
+                        mod_timer(&tun->flow_gc_timer,
+                                  round_jiffies_up(jiffies + delay));
+                spin_unlock_bh(&tun->lock);
+        }
+
+unlock:
+        rcu_read_unlock();
+}
+
 /* We try to identify a flow through its rxhash first. The reason that
  * we do not check rxq no. is becuase some cards(e.g 82599), chooses
  * the rxq based on the txq where the last packet of the flow comes. As
@@ -175,6 +345,7 @@ struct tun_struct {
 static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb)
 {
         struct tun_struct *tun = netdev_priv(dev);
+        struct tun_flow_entry *e;
         u32 txq = 0;
         u32 numqueues = 0;
 
@@ -183,8 +354,12 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb)
 
         txq = skb_get_rxhash(skb);
         if (txq) {
-                /* use multiply and shift instead of expensive divide */
-                txq = ((u64)txq * numqueues) >> 32;
+                e = tun_flow_find(&tun->flows[tun_hashfn(txq)], txq);
+                if (e)
+                        txq = e->queue_index;
+                else
+                        /* use multiply and shift instead of expensive divide */
+                        txq = ((u64)txq * numqueues) >> 32;
         } else if (likely(skb_rx_queue_recorded(skb))) {
                 txq = skb_get_rx_queue(skb);
                 while (unlikely(txq >= numqueues))
@@ -234,6 +409,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
                 sock_put(&tfile->sk);
 
                 synchronize_net();
+                tun_flow_delete_by_queue(tun, tun->numqueues + 1);
                 /* Drop read queue */
                 skb_queue_purge(&tfile->sk.sk_receive_queue);
                 tun_set_real_num_queues(tun);
@@ -631,6 +807,37 @@ static const struct net_device_ops tap_netdev_ops = {
 #endif
 };
 
+static int tun_flow_init(struct tun_struct *tun)
+{
+        int i;
+
+        tun->flow_cache = kmem_cache_create("tun_flow_cache",
+                                            sizeof(struct tun_flow_entry), 0, 0,
+                                            NULL);
+        if (!tun->flow_cache)
+                return -ENOMEM;
+
+        for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++)
+                INIT_HLIST_HEAD(&tun->flows[i]);
+
+        tun->ageing_time = TUN_FLOW_EXPIRE;
+        setup_timer(&tun->flow_gc_timer, tun_flow_cleanup, (unsigned long)tun);
+        mod_timer(&tun->flow_gc_timer,
+                  round_jiffies_up(jiffies + tun->ageing_time));
+
+        return 0;
+}
+
+static void tun_flow_uninit(struct tun_struct *tun)
+{
+        del_timer_sync(&tun->flow_gc_timer);
+        tun_flow_flush(tun);
+
+        /* Wait for completion of call_rcu()'s */
+        rcu_barrier();
+        kmem_cache_destroy(tun->flow_cache);
+}
+
 /* Initialize net device. */
 static void tun_net_init(struct net_device *dev)
 {
@@ -973,6 +1180,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
         tun->dev->stats.rx_packets++;
         tun->dev->stats.rx_bytes += len;
 
+        tun_flow_update(tun, skb, tfile->queue_index);
         return total_len;
 }
 
@@ -1150,6 +1358,14 @@ out:
         return ret;
 }
 
+static void tun_free_netdev(struct net_device *dev)
+{
+        struct tun_struct *tun = netdev_priv(dev);
+
+        tun_flow_uninit(tun);
+        free_netdev(dev);
+}
+
 static void tun_setup(struct net_device *dev)
 {
         struct tun_struct *tun = netdev_priv(dev);
@@ -1158,7 +1374,7 @@ static void tun_setup(struct net_device *dev)
         tun->group = INVALID_GID;
 
         dev->ethtool_ops = &tun_ethtool_ops;
-        dev->destructor = free_netdev;
+        dev->destructor = tun_free_netdev;
 }
 
 /* Trivial set of netlink ops to allow deleting tun or tap
@@ -1381,10 +1597,15 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                 tun->filter_attached = false;
                 tun->sndbuf = tfile->socket.sk->sk_sndbuf;
 
+                spin_lock_init(&tun->lock);
+
                 security_tun_dev_post_create(&tfile->sk);
 
                 tun_net_init(dev);
 
+                if (tun_flow_init(tun))
+                        goto err_free_dev;
+
                 dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
                         TUN_USER_FEATURES;
                 dev->features = dev->hw_features;