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authorEric Dumazet <edumazet@google.com>2016-12-05 20:57:19 +0300
committerDavid S. Miller <davem@davemloft.net>2016-12-06 18:41:49 +0300
commita297569fe00a8fae18547061d355c45ef191b483 (patch)
tree6da37334eacf68c6d214d41e810eaa251a7708be /net/core
parente466af66c768a2a89f5359fdb330b93da799cc55 (diff)
downloadlinux-a297569fe00a8fae18547061d355c45ef191b483.tar.xz
net/udp: do not touch skb->peeked unless really needed
In UDP recvmsg() path we currently access 3 cache lines from an skb while holding receive queue lock, plus another one if packet is dequeued, since we need to change skb->next->prev 1st cache line (contains ->next/prev pointers, offsets 0x00 and 0x08) 2nd cache line (skb->len & skb->peeked, offsets 0x80 and 0x8e) 3rd cache line (skb->truesize/users, offsets 0xe0 and 0xe4) skb->peeked is only needed to make sure 0-length packets are properly handled while MSG_PEEK is operated. I had first the intent to remove skb->peeked but the "MSG_PEEK at non-zero offset" support added by Sam Kumar makes this not possible. This patch avoids one cache line miss during the locked section, when skb->len and skb->peeked do not have to be read. It also avoids the skb_set_peeked() cost for non empty UDP datagrams. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/datagram.c19
1 files changed, 10 insertions, 9 deletions
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 49816af8586b..9482037a5c8c 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -214,6 +214,7 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
if (error)
goto no_packet;
+ *peeked = 0;
do {
/* Again only user level code calls this function, so nothing
* interrupt level will suddenly eat the receive_queue.
@@ -227,22 +228,22 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
spin_lock_irqsave(&queue->lock, cpu_flags);
skb_queue_walk(queue, skb) {
*last = skb;
- *peeked = skb->peeked;
if (flags & MSG_PEEK) {
if (_off >= skb->len && (skb->len || _off ||
skb->peeked)) {
_off -= skb->len;
continue;
}
-
- skb = skb_set_peeked(skb);
- error = PTR_ERR(skb);
- if (IS_ERR(skb)) {
- spin_unlock_irqrestore(&queue->lock,
- cpu_flags);
- goto no_packet;
+ if (!skb->len) {
+ skb = skb_set_peeked(skb);
+ if (IS_ERR(skb)) {
+ error = PTR_ERR(skb);
+ spin_unlock_irqrestore(&queue->lock,
+ cpu_flags);
+ goto no_packet;
+ }
}
-
+ *peeked = 1;
atomic_inc(&skb->users);
} else {
__skb_unlink(skb, queue);