On Mon, Jan 17, 2011 at 04:11:17PM +0800, Jason Wang wrote:

quoted

We can use lock_sock_fast() instead of lock_sock() in order to get
speedup in peek_head_len().

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/net.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index c32a2e4..50b622a 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c

@@ -211,12 +211,12 @@ static int peek_head_len(struct sock *sk)
 {
 	struct sk_buff *head;
 	int len = 0;
+	bool slow = lock_sock_fast(sk);
 
-	lock_sock(sk);
 	head = skb_peek(&sk->sk_receive_queue);
 	if (head)
 		len = head->len;
-	release_sock(sk);
+	unlock_sock_fast(sk, slow);
 	return len;
 }
 

Wanted to apply this, but looking at the code I think the lock_sock here
is wrong. What we really need is to handle the case where the skb is
pulled from the receive queue after skb_peek.  However this is not the
right lock to use for that, sk_receive_queue.lock is.
So I expect the following is the right way to handle this.
Comments?

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 0329c41..5720301 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c

@@ -213,12 +213,13 @@ static int peek_head_len(struct sock *sk)
 {
 	struct sk_buff *head;
 	int len = 0;
+	unsigned long flags;
 
-	lock_sock(sk);
+	spin_lock_irqsave(&sk->sk_receive_queue.lock, flags);
 	head = skb_peek(&sk->sk_receive_queue);
-	if (head)
+	if (likely(head))
 		len = head->len;
-	release_sock(sk);
+	spin_unlock_irqrestore(&sk->sk_receive_queue.lock, flags);
 	return len;
 }