[INET]: Remove per bucket rwlock in tcp/dccp ehash table.

As done two years ago on IP route cache table (commit
22c047ccbc68fa8f3fa57f0e8f906479a062c426) , we can avoid using one
lock per hash bucket for the huge TCP/DCCP hash tables.

On a typical x86_64 platform, this saves about 2MB or 4MB of ram, for
litle performance differences. (we hit a different cache line for the
rwlock, but then the bucket cache line have a better sharing factor
among cpus, since we dirty it less often). For netstat or ss commands
that want a full scan of hash table, we perform fewer memory accesses.

Using a 'small' table of hashed rwlocks should be more than enough to
provide correct SMP concurrency between different buckets, without
using too much memory. Sizing of this table depends on
num_possible_cpus() and various CONFIG settings.

This patch provides some locking abstraction that may ease a future
work using a different model for TCP/DCCP table.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 5 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index e9127cdced20..e566f3c67677 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2049,8 +2049,9 @@ static void *established_get_first(struct seq_file *seq)
                 struct sock *sk;
                 struct hlist_node *node;
                 struct inet_timewait_sock *tw;
+                rwlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
 
-                read_lock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+                read_lock_bh(lock);
                 sk_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
                         if (sk->sk_family != st->family) {
                                 continue;
@@ -2067,7 +2068,7 @@ static void *established_get_first(struct seq_file *seq)
                         rc = tw;
                         goto out;
                 }
-                read_unlock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+                read_unlock_bh(lock);
                 st->state = TCP_SEQ_STATE_ESTABLISHED;
         }
 out:
@@ -2094,11 +2095,11 @@ get_tw:
                         cur = tw;
                         goto out;
                 }
-                read_unlock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+                read_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
                 st->state = TCP_SEQ_STATE_ESTABLISHED;
 
                 if (++st->bucket < tcp_hashinfo.ehash_size) {
-                        read_lock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+                        read_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
                         sk = sk_head(&tcp_hashinfo.ehash[st->bucket].chain);
                 } else {
                         cur = NULL;
@@ -2206,7 +2207,7 @@ static void tcp_seq_stop(struct seq_file *seq, void *v)
         case TCP_SEQ_STATE_TIME_WAIT:
         case TCP_SEQ_STATE_ESTABLISHED:
                 if (v)
-                        read_unlock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+                        read_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
                 break;
         }
 }