From cd7d8498c9a5d510c64db38d9f4f4fbc41790f09 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 24 Sep 2014 04:11:22 -0700 Subject: [PATCH] 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 --- include/net/tcp.h | 23 +++++++++++++++++++++-- net/ipv4/tcp.c | 4 ++-- net/ipv4/tcp_input.c | 8 ++++---- net/ipv4/tcp_output.c | 9 ++++++--- 4 files changed, 33 insertions(+), 11 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 4dc6641ee990..02a9a2c366bf 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -698,7 +698,16 @@ static inline u32 tcp_skb_timestamp(const struct sk_buff *skb) struct tcp_skb_cb { __u32 seq; /* Starting sequence number */ __u32 end_seq; /* SEQ + FIN + SYN + datalen */ - __u32 tcp_tw_isn; /* isn chosen by tcp_timewait_state_process() */ + union { + /* Note : tcp_tw_isn is used in input path only + * (isn chosen by tcp_timewait_state_process()) + * + * tcp_gso_segs is used in write queue only, + * cf tcp_skb_pcount() + */ + __u32 tcp_tw_isn; + __u32 tcp_gso_segs; + }; __u8 tcp_flags; /* TCP header flags. (tcp[13]) */ __u8 sacked; /* State flags for SACK/FACK. */ @@ -746,7 +755,17 @@ TCP_ECN_create_request(struct request_sock *req, const struct sk_buff *skb, */ static inline int tcp_skb_pcount(const struct sk_buff *skb) { - return skb_shinfo(skb)->gso_segs; + return TCP_SKB_CB(skb)->tcp_gso_segs; +} + +static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs) +{ + TCP_SKB_CB(skb)->tcp_gso_segs = segs; +} + +static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs) +{ + TCP_SKB_CB(skb)->tcp_gso_segs += segs; } /* This is valid iff tcp_skb_pcount() > 1. */ diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 553b01f52f71..87289e51be00 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -963,7 +963,7 @@ new_segment: skb->ip_summed = CHECKSUM_PARTIAL; tp->write_seq += copy; TCP_SKB_CB(skb)->end_seq += copy; - skb_shinfo(skb)->gso_segs = 0; + tcp_skb_pcount_set(skb, 0); if (!copied) TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH; @@ -1261,7 +1261,7 @@ new_segment: tp->write_seq += copy; TCP_SKB_CB(skb)->end_seq += copy; - skb_shinfo(skb)->gso_segs = 0; + tcp_skb_pcount_set(skb, 0); from += copy; copied += copy; 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; } diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index a462fb1db896..4d92703df4c6 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -384,7 +384,7 @@ static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags) TCP_SKB_CB(skb)->tcp_flags = flags; TCP_SKB_CB(skb)->sacked = 0; - shinfo->gso_segs = 1; + tcp_skb_pcount_set(skb, 1); shinfo->gso_size = 0; shinfo->gso_type = 0; @@ -972,6 +972,9 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb)); + /* OK, its time to fill skb_shinfo(skb)->gso_segs */ + skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb); + /* Our usage of tstamp should remain private */ skb->tstamp.tv64 = 0; @@ -1019,11 +1022,11 @@ static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb, /* Avoid the costly divide in the normal * non-TSO case. */ - shinfo->gso_segs = 1; + tcp_skb_pcount_set(skb, 1); shinfo->gso_size = 0; shinfo->gso_type = 0; } else { - shinfo->gso_segs = DIV_ROUND_UP(skb->len, mss_now); + tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now)); shinfo->gso_size = mss_now; shinfo->gso_type = sk->sk_gso_type; } -- 2.39.2