From cd7d8498c9a5d510c64db38d9f4f4fbc41790f09 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 24 Sep 2014 04:11:22 -0700 Subject: tcp: change tcp_skb_pcount() location Our goal is to access no more than one cache line access per skb in a write or receive queue when doing the various walks. After recent TCP_SKB_CB() reorganizations, it is almost done. Last part is tcp_skb_pcount() which currently uses skb_shinfo(skb)->gso_segs, which is a terrible choice, because it needs 3 cache lines in current kernel (skb->head, skb->end, and shinfo->gso_segs are all in 3 different cache lines, far from skb->cb) This very simple patch reuses space currently taken by tcp_tw_isn only in input path, as tcp_skb_pcount is only needed for skb stored in write queue. This considerably speeds up tcp_ack(), granted we avoid shinfo->tx_flags to get SKBTX_ACK_TSTAMP, which seems possible. This also speeds up all sack processing in general. This speeds up tcp_sendmsg() because it no longer has to access/dirty shinfo. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'net/ipv4/tcp_input.c') diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index f3f016a15c5a..2c0af90231cf 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1295,9 +1295,9 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb, TCP_SKB_CB(prev)->end_seq += shifted; TCP_SKB_CB(skb)->seq += shifted; - skb_shinfo(prev)->gso_segs += pcount; - BUG_ON(skb_shinfo(skb)->gso_segs < pcount); - skb_shinfo(skb)->gso_segs -= pcount; + tcp_skb_pcount_add(prev, pcount); + BUG_ON(tcp_skb_pcount(skb) < pcount); + tcp_skb_pcount_add(skb, -pcount); /* When we're adding to gso_segs == 1, gso_size will be zero, * in theory this shouldn't be necessary but as long as DSACK @@ -1310,7 +1310,7 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb, } /* CHECKME: To clear or not to clear? Mimics normal skb currently */ - if (skb_shinfo(skb)->gso_segs <= 1) { + if (tcp_skb_pcount(skb) <= 1) { skb_shinfo(skb)->gso_size = 0; skb_shinfo(skb)->gso_type = 0; } -- cgit v1.2.3