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RDS: Change send lock from a mutex to a spinlock

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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>
This commit is contained in:
Andy Grover
2010-03-23 17:39:07 -07:00
parent f17a1a55fb
commit 049ee3f500
4 changed files with 18 additions and 29 deletions
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15
net/rds/send.c
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@@ -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);