RDS: make socket bind/release locking scheme simple and more efficient

RDS bind and release locking scheme is very inefficient. It
uses RCU for maintaining the bind hash-table which is great but
it also needs to hold spinlock for [add/remove]_bound(). So
overall usecase, the hash-table concurrent speedup doesn't pay off.
In fact blocking nature of synchronize_rcu() makes the RDS
socket shutdown too slow which hurts RDS performance since
connection shutdown and re-connect happens quite often to
maintain the RC part of the protocol.

So we make the locking scheme simpler and more efficient by
replacing spin_locks with reader/writer locks and getting rid
off rcu for bind hash-table.

In subsequent patch, we also covert the global lock with per-bucket
lock to reduce the global lock contention.

Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
index a2f28a6..dc08766 100644 (file)
--- a/net/rds/af_rds.c
+++ b/net/rds/af_rds.c
@@ -72,13 +72,7 @@ static int rds_release(struct socket *sock)
        rds_clear_recv_queue(rs);
        rds_cong_remove_socket(rs);
 
-       /*
-        * the binding lookup hash uses rcu, we need to
-        * make sure we synchronize_rcu before we free our
-        * entry
-        */
        rds_remove_bound(rs);
-       synchronize_rcu();
 
        rds_send_drop_to(rs, NULL);
        rds_rdma_drop_keys(rs);

diff --git a/net/rds/bind.c b/net/rds/bind.c
index dd666fb..01989e2 100644 (file)
--- a/net/rds/bind.c
+++ b/net/rds/bind.c
@@ -40,7 +40,7 @@
 
 #define BIND_HASH_SIZE 1024
 static struct hlist_head bind_hash_table[BIND_HASH_SIZE];
-static DEFINE_SPINLOCK(rds_bind_lock);
+static DEFINE_RWLOCK(rds_bind_lock);
 
 static struct hlist_head *hash_to_bucket(__be32 addr, __be16 port)
 {
@@ -48,6 +48,7 @@ static struct hlist_head *hash_to_bucket(__be32 addr, __be16 port)
                                  (BIND_HASH_SIZE - 1));
 }
 
+/* must hold either read or write lock (write lock for insert != NULL) */
 static struct rds_sock *rds_bind_lookup(__be32 addr, __be16 port,
                                        struct rds_sock *insert)
 {
@@ -56,30 +57,24 @@ static struct rds_sock *rds_bind_lookup(__be32 addr, __be16 port,
        u64 cmp;
        u64 needle = ((u64)be32_to_cpu(addr) << 32) | be16_to_cpu(port);
 
-       rcu_read_lock();
-       hlist_for_each_entry_rcu(rs, head, rs_bound_node) {
+       hlist_for_each_entry(rs, head, rs_bound_node) {
                cmp = ((u64)be32_to_cpu(rs->rs_bound_addr) << 32) |
                      be16_to_cpu(rs->rs_bound_port);
 
-               if (cmp == needle) {
-                       rcu_read_unlock();
+               if (cmp == needle)
                        return rs;
-               }
        }
-       rcu_read_unlock();
 
        if (insert) {
                /*
                 * make sure our addr and port are set before
-                * we are added to the list, other people
-                * in rcu will find us as soon as the
-                * hlist_add_head_rcu is done
+                * we are added to the list.
                 */
                insert->rs_bound_addr = addr;
                insert->rs_bound_port = port;
                rds_sock_addref(insert);
 
-               hlist_add_head_rcu(&insert->rs_bound_node, head);
+               hlist_add_head(&insert->rs_bound_node, head);
        }
        return NULL;
 }
@@ -93,8 +88,11 @@ static struct rds_sock *rds_bind_lookup(__be32 addr, __be16 port,
 struct rds_sock *rds_find_bound(__be32 addr, __be16 port)
 {
        struct rds_sock *rs;
+       unsigned long flags;
 
+       read_lock_irqsave(&rds_bind_lock, flags);
        rs = rds_bind_lookup(addr, port, NULL);
+       read_unlock_irqrestore(&rds_bind_lock, flags);
 
        if (rs && !sock_flag(rds_rs_to_sk(rs), SOCK_DEAD))
                rds_sock_addref(rs);
@@ -103,6 +101,7 @@ struct rds_sock *rds_find_bound(__be32 addr, __be16 port)
 
        rdsdebug("returning rs %p for %pI4:%u\n", rs, &addr,
                ntohs(port));
+
        return rs;
 }
 
@@ -121,7 +120,7 @@ static int rds_add_bound(struct rds_sock *rs, __be32 addr, __be16 *port)
                last = rover - 1;
        }
 
-       spin_lock_irqsave(&rds_bind_lock, flags);
+       write_lock_irqsave(&rds_bind_lock, flags);
 
        do {
                if (rover == 0)
@@ -135,7 +134,7 @@ static int rds_add_bound(struct rds_sock *rs, __be32 addr, __be16 *port)
                }
        } while (rover++ != last);
 
-       spin_unlock_irqrestore(&rds_bind_lock, flags);
+       write_unlock_irqrestore(&rds_bind_lock, flags);
 
        return ret;
 }
@@ -144,19 +143,19 @@ void rds_remove_bound(struct rds_sock *rs)
 {
        unsigned long flags;
 
-       spin_lock_irqsave(&rds_bind_lock, flags);
+       write_lock_irqsave(&rds_bind_lock, flags);
 
        if (rs->rs_bound_addr) {
                rdsdebug("rs %p unbinding from %pI4:%d\n",
                  rs, &rs->rs_bound_addr,
                  ntohs(rs->rs_bound_port));
 
-               hlist_del_init_rcu(&rs->rs_bound_node);
+               hlist_del_init(&rs->rs_bound_node);
                rds_sock_put(rs);
                rs->rs_bound_addr = 0;
        }
 
-       spin_unlock_irqrestore(&rds_bind_lock, flags);
+       write_unlock_irqrestore(&rds_bind_lock, flags);
 }
 
 int rds_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
@@ -200,9 +199,5 @@ int rds_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 
 out:
        release_sock(sk);
-
-       /* we might have called rds_remove_bound on error */
-       if (ret)
-               synchronize_rcu();
        return ret;
 }