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authorEric Dumazet <edumazet@google.com>2016-12-08 11:41:55 -0800
committerDavid S. Miller <davem@davemloft.net>2016-12-09 22:12:21 -0500
commitc84d949057cab262b4d3110ead9a42a58c2958f7 (patch)
tree000d71e4f8d508764105d9e4d8b20ff86c5b9eab
parent4b272750dbe6f92a8d39a0ee1c7bd50d6cc1a2c8 (diff)
downloadlinux-c84d949057cab262b4d3110ead9a42a58c2958f7.tar.bz2
udp: copy skb->truesize in the first cache line
In UDP RX handler, we currently clear skb->dev before skb is added to receive queue, because device pointer is no longer available once we exit from RCU section. Since this first cache line is always hot, lets reuse this space to store skb->truesize and thus avoid a cache line miss at udp_recvmsg()/udp_skb_destructor time while receive queue spinlock is held. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/skbuff.h9
-rw-r--r--net/ipv4/udp.c13
2 files changed, 18 insertions, 4 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 0cd92b0f2af5..332e76756f54 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -645,8 +645,15 @@ struct sk_buff {
struct rb_node rbnode; /* used in netem & tcp stack */
};
struct sock *sk;
- struct net_device *dev;
+ union {
+ struct net_device *dev;
+ /* Some protocols might use this space to store information,
+ * while device pointer would be NULL.
+ * UDP receive path is one user.
+ */
+ unsigned long dev_scratch;
+ };
/*
* This is the control buffer. It is free to use for every
* layer. Please put your private variables there. If you
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e6a68d66f3b2..c608334d99aa 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1188,10 +1188,14 @@ static void udp_rmem_release(struct sock *sk, int size, int partial)
__sk_mem_reduce_allocated(sk, amt >> SK_MEM_QUANTUM_SHIFT);
}
-/* Note: called with sk_receive_queue.lock held */
+/* Note: called with sk_receive_queue.lock held.
+ * Instead of using skb->truesize here, find a copy of it in skb->dev_scratch
+ * This avoids a cache line miss while receive_queue lock is held.
+ * Look at __udp_enqueue_schedule_skb() to find where this copy is done.
+ */
void udp_skb_destructor(struct sock *sk, struct sk_buff *skb)
{
- udp_rmem_release(sk, skb->truesize, 1);
+ udp_rmem_release(sk, skb->dev_scratch, 1);
}
EXPORT_SYMBOL(udp_skb_destructor);
@@ -1246,6 +1250,10 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
busy = busylock_acquire(sk);
}
size = skb->truesize;
+ /* Copy skb->truesize into skb->dev_scratch to avoid a cache line miss
+ * in udp_skb_destructor()
+ */
+ skb->dev_scratch = size;
/* we drop only if the receive buf is full and the receive
* queue contains some other skb
@@ -1272,7 +1280,6 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
/* no need to setup a destructor, we will explicitly release the
* forward allocated memory on dequeue
*/
- skb->dev = NULL;
sock_skb_set_dropcount(sk, skb);
__skb_queue_tail(list, skb);