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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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22
net/rds/connection.c
View File

@ -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,

6
net/rds/rds.h
View File

@ -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;

15
net/rds/send.c
View File

@ -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);

4
net/rds/stats.c
View File

@ -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",