inetpeer: various changes

Try to reduce cache line contentions in peer management, to reduce IP
defragmentation overhead.

- peer_fake_node is marked 'const' to make sure its not modified.
  (tested with CONFIG_DEBUG_RODATA=y)

- Group variables in two structures to reduce number of dirtied cache
lines. One named "peers" for avl tree root, its number of entries, and
associated lock. (candidate for RCU conversion)

- A second one named "unused_peers" for unused list and its lock

- Add a !list_empty() test in unlink_from_unused() to avoid taking lock
when entry is not unused.

- Use atomic_dec_and_lock() in inet_putpeer() to avoid taking lock in
some cases.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 56 insertions, 38 deletions

diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index 6bcfe52a9c87..035673fd42d4 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -70,17 +70,25 @@
 static struct kmem_cache *peer_cachep __read_mostly;
 
 #define node_height(x) x->avl_height
-static struct inet_peer peer_fake_node = {
-        .avl_left       = &peer_fake_node,
-        .avl_right      = &peer_fake_node,
+
+#define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
+static const struct inet_peer peer_fake_node = {
+        .avl_left       = peer_avl_empty,
+        .avl_right      = peer_avl_empty,
         .avl_height     = 0
 };
-#define peer_avl_empty (&peer_fake_node)
-static struct inet_peer *peer_root = peer_avl_empty;
-static DEFINE_RWLOCK(peer_pool_lock);
+
+static struct {
+        struct inet_peer *root;
+        rwlock_t        lock;
+        int             total;
+} peers = {
+        .root           = peer_avl_empty,
+        .lock           = __RW_LOCK_UNLOCKED(peers.lock),
+        .total          = 0,
+};
 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
 
-static int peer_total;
 /* Exported for sysctl_net_ipv4.  */
 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
                                          * aggressively at this stage */
@@ -89,8 +97,13 @@ int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;	/* usual time to live: 10 min
 int inet_peer_gc_mintime __read_mostly = 10 * HZ;
 int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
 
-static LIST_HEAD(unused_peers);
-static DEFINE_SPINLOCK(inet_peer_unused_lock);
+static struct {
+        struct list_head        list;
+        spinlock_t              lock;
+} unused_peers = {
+        .list                   = LIST_HEAD_INIT(unused_peers.list),
+        .lock                   = __SPIN_LOCK_UNLOCKED(unused_peers.lock),
+};
 
 static void peer_check_expire(unsigned long dummy);
 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
@@ -131,9 +144,11 @@ void __init inet_initpeers(void)
 /* Called with or without local BH being disabled. */
 static void unlink_from_unused(struct inet_peer *p)
 {
-        spin_lock_bh(&inet_peer_unused_lock);
-        list_del_init(&p->unused);
-        spin_unlock_bh(&inet_peer_unused_lock);
+        if (!list_empty(&p->unused)) {
+                spin_lock_bh(&unused_peers.lock);
+                list_del_init(&p->unused);
+                spin_unlock_bh(&unused_peers.lock);
+        }
 }
 
 /*
@@ -146,9 +161,9 @@ static void unlink_from_unused(struct inet_peer *p)
         struct inet_peer *u, **v;                               \
         if (_stack != NULL) {                                   \
                 stackptr = _stack;                              \
-                *stackptr++ = &peer_root;                       \
+                *stackptr++ = &peers.root;                      \
         }                                                       \
-        for (u = peer_root; u != peer_avl_empty; ) {            \
+        for (u = peers.root; u != peer_avl_empty; ) {           \
                 if (_daddr == u->v4daddr)                       \
                         break;                                  \
                 if ((__force __u32)_daddr < (__force __u32)u->v4daddr)  \
@@ -262,7 +277,7 @@ do {								\
         n->avl_right = peer_avl_empty;                          \
         **--stackptr = n;                                       \
         peer_avl_rebalance(stack, stackptr);                    \
-} while(0)
+} while (0)
 
 /* May be called with local BH enabled. */
 static void unlink_from_pool(struct inet_peer *p)
@@ -271,7 +286,7 @@ static void unlink_from_pool(struct inet_peer *p)
 
         do_free = 0;
 
-        write_lock_bh(&peer_pool_lock);
+        write_lock_bh(&peers.lock);
         /* Check the reference counter.  It was artificially incremented by 1
          * in cleanup() function to prevent sudden disappearing.  If the
          * reference count is still 1 then the node is referenced only as `p'
@@ -303,10 +318,10 @@ static void unlink_from_pool(struct inet_peer *p)
                         delp[1] = &t->avl_left; /* was &p->avl_left */
                 }
                 peer_avl_rebalance(stack, stackptr);
-                peer_total--;
+                peers.total--;
                 do_free = 1;
         }
-        write_unlock_bh(&peer_pool_lock);
+        write_unlock_bh(&peers.lock);
 
         if (do_free)
                 kmem_cache_free(peer_cachep, p);
@@ -326,16 +341,16 @@ static int cleanup_once(unsigned long ttl)
         struct inet_peer *p = NULL;
 
         /* Remove the first entry from the list of unused nodes. */
-        spin_lock_bh(&inet_peer_unused_lock);
-        if (!list_empty(&unused_peers)) {
+        spin_lock_bh(&unused_peers.lock);
+        if (!list_empty(&unused_peers.list)) {
                 __u32 delta;
 
-                p = list_first_entry(&unused_peers, struct inet_peer, unused);
+                p = list_first_entry(&unused_peers.list, struct inet_peer, unused);
                 delta = (__u32)jiffies - p->dtime;
 
                 if (delta < ttl) {
                         /* Do not prune fresh entries. */
-                        spin_unlock_bh(&inet_peer_unused_lock);
+                        spin_unlock_bh(&unused_peers.lock);
                         return -1;
                 }
 
@@ -345,7 +360,7 @@ static int cleanup_once(unsigned long ttl)
                  * before unlink_from_pool() call. */
                 atomic_inc(&p->refcnt);
         }
-        spin_unlock_bh(&inet_peer_unused_lock);
+        spin_unlock_bh(&unused_peers.lock);
 
         if (p == NULL)
                 /* It means that the total number of USED entries has
@@ -364,11 +379,11 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
         struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
 
         /* Look up for the address quickly. */
-        read_lock_bh(&peer_pool_lock);
+        read_lock_bh(&peers.lock);
         p = lookup(daddr, NULL);
         if (p != peer_avl_empty)
                 atomic_inc(&p->refcnt);
-        read_unlock_bh(&peer_pool_lock);
+        read_unlock_bh(&peers.lock);
 
         if (p != peer_avl_empty) {
                 /* The existing node has been found. */
@@ -390,7 +405,7 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
         atomic_set(&n->ip_id_count, secure_ip_id(daddr));
         n->tcp_ts_stamp = 0;
 
-        write_lock_bh(&peer_pool_lock);
+        write_lock_bh(&peers.lock);
         /* Check if an entry has suddenly appeared. */
         p = lookup(daddr, stack);
         if (p != peer_avl_empty)
@@ -399,10 +414,10 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
         /* Link the node. */
         link_to_pool(n);
         INIT_LIST_HEAD(&n->unused);
-        peer_total++;
-        write_unlock_bh(&peer_pool_lock);
+        peers.total++;
+        write_unlock_bh(&peers.lock);
 
-        if (peer_total >= inet_peer_threshold)
+        if (peers.total >= inet_peer_threshold)
                 /* Remove one less-recently-used entry. */
                 cleanup_once(0);
 
@@ -411,7 +426,7 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
 out_free:
         /* The appropriate node is already in the pool. */
         atomic_inc(&p->refcnt);
-        write_unlock_bh(&peer_pool_lock);
+        write_unlock_bh(&peers.lock);
         /* Remove the entry from unused list if it was there. */
         unlink_from_unused(p);
         /* Free preallocated the preallocated node. */
@@ -425,12 +440,12 @@ static void peer_check_expire(unsigned long dummy)
         unsigned long now = jiffies;
         int ttl;
 
-        if (peer_total >= inet_peer_threshold)
+        if (peers.total >= inet_peer_threshold)
                 ttl = inet_peer_minttl;
         else
                 ttl = inet_peer_maxttl
                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
-                                        peer_total / inet_peer_threshold * HZ;
+                                        peers.total / inet_peer_threshold * HZ;
         while (!cleanup_once(ttl)) {
                 if (jiffies != now)
                         break;
@@ -439,22 +454,25 @@ static void peer_check_expire(unsigned long dummy)
         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
          * interval depending on the total number of entries (more entries,
          * less interval). */
-        if (peer_total >= inet_peer_threshold)
+        if (peers.total >= inet_peer_threshold)
                 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
         else
                 peer_periodic_timer.expires = jiffies
                         + inet_peer_gc_maxtime
                         - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
-                                peer_total / inet_peer_threshold * HZ;
+                                peers.total / inet_peer_threshold * HZ;
         add_timer(&peer_periodic_timer);
 }
 
 void inet_putpeer(struct inet_peer *p)
 {
-        spin_lock_bh(&inet_peer_unused_lock);
-        if (atomic_dec_and_test(&p->refcnt)) {
-                list_add_tail(&p->unused, &unused_peers);
+        local_bh_disable();
+
+        if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
+                list_add_tail(&p->unused, &unused_peers.list);
                 p->dtime = (__u32)jiffies;
+                spin_unlock(&unused_peers.lock);
         }
-        spin_unlock_bh(&inet_peer_unused_lock);
+
+        local_bh_enable();
 }