From 049ee3f500954176a87f22e6ee3e98aecb1b8958 Mon Sep 17 00:00:00 2001 From: Andy Grover Date: Tue, 23 Mar 2010 17:39:07 -0700 Subject: [PATCH] RDS: Change send lock from a mutex to a spinlock This change allows us to call rds_send_xmit() from a tasklet, which is crucial to our new operating model. * Change c_send_lock to a spinlock * Update stats fields "sem_" to "_lock" * Remove unneeded rds_conn_is_sending() About locking between shutdown and send -- send checks if the connection is up. Shutdown puts the connection into DISCONNECTING. After this, all threads entering send will exit immediately. However, a thread could be *in* send_xmit(), so shutdown acquires the c_send_lock to ensure everyone is out before proceeding with connection shutdown. Signed-off-by: Andy Grover --- net/rds/connection.c | 22 ++++++---------------- net/rds/rds.h | 6 +++--- net/rds/send.c | 15 +++++++-------- net/rds/stats.c | 4 ++-- 4 files changed, 18 insertions(+), 29 deletions(-) diff --git a/net/rds/connection.c b/net/rds/connection.c index 88bcaf3f3e1..56aebe444ad 100644 --- a/net/rds/connection.c +++ b/net/rds/connection.c @@ -62,18 +62,6 @@ static struct hlist_head *rds_conn_bucket(__be32 laddr, __be32 faddr) var |= RDS_INFO_CONNECTION_FLAG_##suffix; \ } while (0) -static inline int rds_conn_is_sending(struct rds_connection *conn) -{ - int ret = 0; - - if (!mutex_trylock(&conn->c_send_lock)) - ret = 1; - else - mutex_unlock(&conn->c_send_lock); - - return ret; -} - static struct rds_connection *rds_conn_lookup(struct hlist_head *head, __be32 laddr, __be32 faddr, struct rds_transport *trans) @@ -158,7 +146,7 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr, spin_lock_init(&conn->c_lock); conn->c_next_tx_seq = 1; - mutex_init(&conn->c_send_lock); + spin_lock_init(&conn->c_send_lock); INIT_LIST_HEAD(&conn->c_send_queue); INIT_LIST_HEAD(&conn->c_retrans); @@ -283,10 +271,12 @@ void rds_conn_shutdown(struct rds_connection *conn) } mutex_unlock(&conn->c_cm_lock); - mutex_lock(&conn->c_send_lock); + /* verify everybody's out of rds_send_xmit() */ + spin_lock_irq(&conn->c_send_lock); + spin_unlock_irq(&conn->c_send_lock); + conn->c_trans->conn_shutdown(conn); rds_conn_reset(conn); - mutex_unlock(&conn->c_send_lock); if (!rds_conn_transition(conn, RDS_CONN_DISCONNECTING, RDS_CONN_DOWN)) { /* This can happen - eg when we're in the middle of tearing @@ -476,7 +466,7 @@ static int rds_conn_info_visitor(struct rds_connection *conn, cinfo->flags = 0; rds_conn_info_set(cinfo->flags, - rds_conn_is_sending(conn), SENDING); + spin_is_locked(&conn->c_send_lock), SENDING); /* XXX Future: return the state rather than these funky bits */ rds_conn_info_set(cinfo->flags, atomic_read(&conn->c_state) == RDS_CONN_CONNECTING, diff --git a/net/rds/rds.h b/net/rds/rds.h index e81d7e47847..c3a668b9cc1 100644 --- a/net/rds/rds.h +++ b/net/rds/rds.h @@ -91,7 +91,7 @@ struct rds_connection { struct rds_cong_map *c_lcong; struct rds_cong_map *c_fcong; - struct mutex c_send_lock; /* protect send ring */ + spinlock_t c_send_lock; /* protect send ring */ struct rds_message *c_xmit_rm; unsigned long c_xmit_sg; unsigned int c_xmit_hdr_off; @@ -548,8 +548,8 @@ struct rds_statistics { uint64_t s_recv_ping; uint64_t s_send_queue_empty; uint64_t s_send_queue_full; - uint64_t s_send_sem_contention; - uint64_t s_send_sem_queue_raced; + uint64_t s_send_lock_contention; + uint64_t s_send_lock_queue_raced; uint64_t s_send_immediate_retry; uint64_t s_send_delayed_retry; uint64_t s_send_drop_acked; diff --git a/net/rds/send.c b/net/rds/send.c index 8a0647af5d9..d4feec6ad09 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -116,19 +116,18 @@ int rds_send_xmit(struct rds_connection *conn) int was_empty = 0; LIST_HEAD(to_be_dropped); + if (!rds_conn_up(conn)) + goto out; + /* * sendmsg calls here after having queued its message on the send * queue. We only have one task feeding the connection at a time. If * another thread is already feeding the queue then we back off. This * avoids blocking the caller and trading per-connection data between * caches per message. - * - * The sem holder will issue a retry if they notice that someone queued - * a message after they stopped walking the send queue but before they - * dropped the sem. */ - if (!mutex_trylock(&conn->c_send_lock)) { - rds_stats_inc(s_send_sem_contention); + if (!spin_trylock_irqsave(&conn->c_send_lock, flags)) { + rds_stats_inc(s_send_lock_contention); ret = -ENOMEM; goto out; } @@ -346,7 +345,7 @@ int rds_send_xmit(struct rds_connection *conn) * stop processing the loop when the transport hasn't taken * responsibility for forward progress. */ - mutex_unlock(&conn->c_send_lock); + spin_unlock_irqrestore(&conn->c_send_lock, flags); if (send_quota == 0 && !was_empty) { /* We exhausted the send quota, but there's work left to @@ -360,7 +359,7 @@ int rds_send_xmit(struct rds_connection *conn) * spin lock */ spin_lock_irqsave(&conn->c_lock, flags); if (!list_empty(&conn->c_send_queue)) { - rds_stats_inc(s_send_sem_queue_raced); + rds_stats_inc(s_send_lock_queue_raced); ret = -EAGAIN; } spin_unlock_irqrestore(&conn->c_lock, flags); diff --git a/net/rds/stats.c b/net/rds/stats.c index c66d95d9c26..b77be8be33b 100644 --- a/net/rds/stats.c +++ b/net/rds/stats.c @@ -57,8 +57,8 @@ static const char *const rds_stat_names[] = { "recv_ping", "send_queue_empty", "send_queue_full", - "send_sem_contention", - "send_sem_queue_raced", + "send_lock_contention", + "send_lock_queue_raced", "send_immediate_retry", "send_delayed_retry", "send_drop_acked", -- 2.39.3