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tuntap: choose the txq based on rxq
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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>
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@jasowang @davem330
jasowang authored and davem330 committed Nov 1, 2012
1 parent cde8b15 commit 96442e4
Showing 1 changed file with 224 additions and 3 deletions.
227 changes: 224 additions & 3 deletions drivers/net/tun.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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.
Expand All @@ -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
Expand All @@ -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;

Expand All @@ -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))
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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)
{
Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -1150,6 +1358,14 @@ static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
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);
Expand All @@ -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
Expand Down Expand Up @@ -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;
Expand Down

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