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Commit 8b0a6b46 authored by Santosh Shilimkar's avatar Santosh Shilimkar Committed by Santosh Shilimkar
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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: default avatarSantosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: default avatarSantosh Shilimkar <santosh.shilimkar@oracle.com>
parent 59fe4606

net/rds/af_rds.c

+0 −6
Original line number Diff line number Diff line
@@ -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);

net/rds/bind.c

+15 −20
Original line number Diff line number Diff line
@@ -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;

}