[IPV4]: Optimize inet_getpeer()

1) Some sysctl vars are declared __read_mostly

2) We can avoid updating stack[] when doing an AVL lookup only.

    lookup() macro is extended to receive a second parameter, that may be NULL
in case of a pure lookup (no need to save the AVL path). This removes
unnecessary instructions, because compiler knows if this _stack parameter is
NULL or not.

    text size of net/ipv4/inetpeer.o is 2063 bytes instead of 2107 on x86_64

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 16 deletions

diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index db3ef96bdfd9..2f44e6128068 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -87,10 +87,12 @@ static DEFINE_RWLOCK(peer_pool_lock);
 
 static int peer_total;
 /* Exported for sysctl_net_ipv4.  */
-int inet_peer_threshold = 65536 + 128;  /* start to throw entries more
+int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
                                          * aggressively at this stage */
-int inet_peer_minttl = 120 * HZ;        /* TTL under high load: 120 sec */
-int inet_peer_maxttl = 10 * 60 * HZ;    /* usual time to live: 10 min */
+int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
+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 struct inet_peer *inet_peer_unused_head;
 static struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head;
@@ -99,9 +101,6 @@ static DEFINE_SPINLOCK(inet_peer_unused_lock);
 static void peer_check_expire(unsigned long dummy);
 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
 
-/* Exported for sysctl_net_ipv4.  */
-int inet_peer_gc_mintime = 10 * HZ,
-    inet_peer_gc_maxtime = 120 * HZ;
 
 /* Called from ip_output.c:ip_init  */
 void __init inet_initpeers(void)
@@ -151,20 +150,27 @@ static void unlink_from_unused(struct inet_peer *p)
         spin_unlock_bh(&inet_peer_unused_lock);
 }
 
-/* Called with local BH disabled and the pool lock held. */
-#define lookup(daddr)                                           \
+/*
+ * Called with local BH disabled and the pool lock held.
+ * _stack is known to be NULL or not at compile time,
+ * so compiler will optimize the if (_stack) tests.
+ */
+#define lookup(_daddr,_stack)                                   \
 ({                                                              \
         struct inet_peer *u, **v;                               \
-        stackptr = stack;                                       \
-        *stackptr++ = &peer_root;                               \
+        if (_stack) {                                           \
+                stackptr = _stack;                              \
+                *stackptr++ = &peer_root;                       \
+        }                                                       \
         for (u = peer_root; u != peer_avl_empty; ) {            \
-                if (daddr == u->v4daddr)                        \
+                if (_daddr == u->v4daddr)                       \
                         break;                                  \
-                if ((__force __u32)daddr < (__force __u32)u->v4daddr)   \
+                if ((__force __u32)_daddr < (__force __u32)u->v4daddr)  \
                         v = &u->avl_left;                       \
                 else                                            \
                         v = &u->avl_right;                      \
-                *stackptr++ = v;                                \
+                if (_stack)                                     \
+                        *stackptr++ = v;                        \
                 u = *v;                                         \
         }                                                       \
         u;                                                      \
@@ -288,7 +294,7 @@ static void unlink_from_pool(struct inet_peer *p)
         if (atomic_read(&p->refcnt) == 1) {
                 struct inet_peer **stack[PEER_MAXDEPTH];
                 struct inet_peer ***stackptr, ***delp;
-                if (lookup(p->v4daddr) != p)
+                if (lookup(p->v4daddr, stack) != p)
                         BUG();
                 delp = stackptr - 1; /* *delp[0] == p */
                 if (p->avl_left == peer_avl_empty) {
@@ -373,7 +379,7 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
 
         /* Look up for the address quickly. */
         read_lock_bh(&peer_pool_lock);
-        p = lookup(daddr);
+        p = lookup(daddr, NULL);
         if (p != peer_avl_empty)
                 atomic_inc(&p->refcnt);
         read_unlock_bh(&peer_pool_lock);
@@ -400,7 +406,7 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
 
         write_lock_bh(&peer_pool_lock);
         /* Check if an entry has suddenly appeared. */
-        p = lookup(daddr);
+        p = lookup(daddr, stack);
         if (p != peer_avl_empty)
                 goto out_free;