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 <andy.grover@oracle.com>
diff --git a/net/rds/connection.c b/net/rds/connection.c
index 88bcaf3..56aebe4 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -62,18 +62,6 @@
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 @@
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 @@
}
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 @@
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 e81d7e4..c3a668b 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -91,7 +91,7 @@
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 @@
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 8a0647a..d4feec6 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -116,19 +116,18 @@
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 @@
* 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 @@
* 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 c66d95d..b77be8b 100644
--- a/net/rds/stats.c
+++ b/net/rds/stats.c
@@ -57,8 +57,8 @@
"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",