netdev - [PATCH] net/core/sock.c remove extra wakeup

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Date:	Thu, 29 May 2008 10:08:43 -0600
From:	"Patrick Mullaney" <pmullaney@...ell.com>
To:	<davem@...emloft.net>
Cc:	"Gregory Haskins" <GHaskins@...ell.com>, <netdev@...r.kernel.org>
Subject: [PATCH] net/core/sock.c remove extra wakeup


From: Patrick Mullaney <pmullaney@...ell.com>

We have noticed an extra wakeup of a task waiting on a udp receive
while testing with CONFIG_PREEMPT_RT. The following patch
eliminates the source of the extra wakeup by only waking a task
if it is waiting on the writable condition(the SOCK_NOSPACE
bit has been set). The patch is against 2.6.25.

Signed-off-by: Patrick Mullaney <pmullaney@...ell.com>
---

 net/core/sock.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 7a0567b..df08fb2 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1628,12 +1628,17 @@ static void sock_def_readable(struct sock *sk, int len)
 
 static void sock_def_write_space(struct sock *sk)
 {
+	/* don't wake unless writer is waiting */
+	if(!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
+		return;
+
 	read_lock(&sk->sk_callback_lock);
 
 	/* Do not wake up a writer until he can make "significant"
 	 * progress.  --DaveM
 	 */
 	if ((atomic_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf) {
+		clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 		if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
 			wake_up_interruptible_sync(sk->sk_sleep);
 



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