diff options
authorEric Dumazet <dada1@cosmosbay.com>2009-04-28 02:24:21 -0700
committerDavid S. Miller <davem@davemloft.net>2009-04-28 02:24:21 -0700
commitbf368e4e70cd4e0f880923c44e95a4273d725ab4 (patch)
parent37b607c5ac3b7c92a6a3624bb29f1cdcdcf7044a (diff)
net: Avoid extra wakeups of threads blocked in wait_for_packet()
In 2.6.25 we added UDP mem accounting. This unfortunatly added a penalty when a frame is transmitted, since we have at TX completion time to call sock_wfree() to perform necessary memory accounting. This calls sock_def_write_space() and utimately scheduler if any thread is waiting on the socket. Thread(s) waiting for an incoming frame was scheduled, then had to sleep again as event was meaningless. (All threads waiting on a socket are using same sk_sleep anchor) This adds lot of extra wakeups and increases latencies, as noted by Christoph Lameter, and slows down softirq handler. Reference : http://marc.info/?l=linux-netdev&m=124060437012283&w=2 Fortunatly, Davide Libenzi recently added concept of keyed wakeups into kernel, and particularly for sockets (see commit 37e5540b3c9d838eb20f2ca8ea2eb8072271e403 epoll keyed wakeups: make sockets use keyed wakeups) Davide goal was to optimize epoll, but this new wakeup infrastructure can help non epoll users as well, if they care to setup an appropriate handler. This patch introduces new DEFINE_WAIT_FUNC() helper and uses it in wait_for_packet(), so that only relevant event can wakeup a thread blocked in this function. Trace of function calls from bnx2 TX completion bnx2_poll_work() is : __kfree_skb() skb_release_head_state() sock_wfree() sock_def_write_space() __wake_up_sync_key() __wake_up_common() receiver_wake_function() : Stops here since thread is waiting for an INPUT Reported-by: Christoph Lameter <cl@linux.com> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2 files changed, 17 insertions, 3 deletions
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 5d631c17eaee..bc024632f365 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -440,13 +440,15 @@ void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key);
int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *key);
-#define DEFINE_WAIT(name) \
+#define DEFINE_WAIT_FUNC(name, function) \
wait_queue_t name = { \
.private = current, \
- .func = autoremove_wake_function, \
+ .func = function, \
.task_list = LIST_HEAD_INIT((name).task_list), \
+#define DEFINE_WAIT(name) DEFINE_WAIT_FUNC(name, autoremove_wake_function)
#define DEFINE_WAIT_BIT(name, word, bit) \
struct wait_bit_queue name = { \
.key = __WAIT_BIT_KEY_INITIALIZER(word, bit), \
diff --git a/net/core/datagram.c b/net/core/datagram.c
index d0de644b378d..b01a76abe1d2 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -64,13 +64,25 @@ static inline int connection_based(struct sock *sk)
return sk->sk_type == SOCK_SEQPACKET || sk->sk_type == SOCK_STREAM;
+static int receiver_wake_function(wait_queue_t *wait, unsigned mode, int sync,
+ void *key)
+ unsigned long bits = (unsigned long)key;
+ /*
+ * Avoid a wakeup if event not interesting for us
+ */
+ if (bits && !(bits & (POLLIN | POLLERR)))
+ return 0;
+ return autoremove_wake_function(wait, mode, sync, key);
* Wait for a packet..
static int wait_for_packet(struct sock *sk, int *err, long *timeo_p)
int error;
- DEFINE_WAIT(wait);
+ DEFINE_WAIT_FUNC(wait, receiver_wake_function);
prepare_to_wait_exclusive(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);