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[TCP]: Perform setting of common control fields in one place
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In case of segments which are purely for control without any
data (SYN/ACK/FIN/RST), many fields are set to common values
in multiple places.

i386 results:

$ gcc --version
gcc (GCC) 4.1.2 20070626 (Red Hat 4.1.2-13)

$ codiff tcp_output.o.old tcp_output.o.new
net/ipv4/tcp_output.c:
  tcp_xmit_probe_skb    |  -48
  tcp_send_ack          |  -56
  tcp_retransmit_skb    |  -79
  tcp_connect           |  -43
  tcp_send_active_reset |  -35
  tcp_make_synack       |  -42
  tcp_send_fin          |  -48
 7 functions changed, 351 bytes removed

net/ipv4/tcp_output.c:
  tcp_init_nondata_skb |  +90
 1 function changed, 90 bytes added

tcp_output.o.mid:
 8 functions changed, 90 bytes added, 351 bytes removed, diff: -261

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Ilpo Järvinen authored and David S. Miller committed Jan 28, 2008
1 parent 19773b4 commit e870a8e
Showing 1 changed file with 36 additions and 55 deletions.
91 changes: 36 additions & 55 deletions net/ipv4/tcp_output.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -327,6 +327,26 @@ static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
}
}

/* Constructs common control bits of non-data skb. If SYN/FIN is present,
* auto increment end seqno.
*/
static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
{
skb->csum = 0;

TCP_SKB_CB(skb)->flags = flags;
TCP_SKB_CB(skb)->sacked = 0;

skb_shinfo(skb)->gso_segs = 1;
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_type = 0;

TCP_SKB_CB(skb)->seq = seq;
if (flags & (TCPCB_FLAG_SYN | TCPCB_FLAG_FIN))
seq++;
TCP_SKB_CB(skb)->end_seq = seq;
}

static void tcp_build_and_update_options(__be32 *ptr, struct tcp_sock *tp,
__u32 tstamp, __u8 **md5_hash)
{
Expand Down Expand Up @@ -1864,12 +1884,10 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
if (!pskb_trim(skb, 0)) {
TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1;
skb_shinfo(skb)->gso_segs = 1;
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_type = 0;
/* Reuse, even though it does some unnecessary work */
tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
TCP_SKB_CB(skb)->flags);
skb->ip_summed = CHECKSUM_NONE;
skb->csum = 0;
}
}

Expand Down Expand Up @@ -2068,16 +2086,9 @@ void tcp_send_fin(struct sock *sk)

/* Reserve space for headers and prepare control bits. */
skb_reserve(skb, MAX_TCP_HEADER);
skb->csum = 0;
TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
TCP_SKB_CB(skb)->sacked = 0;
skb_shinfo(skb)->gso_segs = 1;
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_type = 0;

/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
TCP_SKB_CB(skb)->seq = tp->write_seq;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
tcp_init_nondata_skb(skb, tp->write_seq,
TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
tcp_queue_skb(sk, skb);
}
__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
Expand All @@ -2101,16 +2112,9 @@ void tcp_send_active_reset(struct sock *sk, gfp_t priority)

/* Reserve space for headers and prepare control bits. */
skb_reserve(skb, MAX_TCP_HEADER);
skb->csum = 0;
TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
TCP_SKB_CB(skb)->sacked = 0;
skb_shinfo(skb)->gso_segs = 1;
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_type = 0;

tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
/* Send it off. */
TCP_SKB_CB(skb)->seq = tcp_acceptable_seq(sk);
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
TCP_SKB_CB(skb)->when = tcp_time_stamp;
if (tcp_transmit_skb(sk, skb, 0, priority))
NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
Expand Down Expand Up @@ -2198,12 +2202,11 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
TCP_ECN_make_synack(req, th);
th->source = inet_sk(sk)->sport;
th->dest = ireq->rmt_port;
TCP_SKB_CB(skb)->seq = tcp_rsk(req)->snt_isn;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
TCP_SKB_CB(skb)->sacked = 0;
skb_shinfo(skb)->gso_segs = 1;
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_type = 0;
/* Setting of flags are superfluous here for callers (and ECE is
* not even correctly set)
*/
tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
TCPCB_FLAG_SYN | TCPCB_FLAG_ACK);
th->seq = htonl(TCP_SKB_CB(skb)->seq);
th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
Expand Down Expand Up @@ -2235,7 +2238,6 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
NULL)
);

skb->csum = 0;
th->doff = (tcp_header_size >> 2);
TCP_INC_STATS(TCP_MIB_OUTSEGS);

Expand Down Expand Up @@ -2327,16 +2329,9 @@ int tcp_connect(struct sock *sk)
/* Reserve space for headers. */
skb_reserve(buff, MAX_TCP_HEADER);

TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN;
TCP_ECN_send_syn(sk, buff);
TCP_SKB_CB(buff)->sacked = 0;
skb_shinfo(buff)->gso_segs = 1;
skb_shinfo(buff)->gso_size = 0;
skb_shinfo(buff)->gso_type = 0;
buff->csum = 0;
tp->snd_nxt = tp->write_seq;
TCP_SKB_CB(buff)->seq = tp->write_seq++;
TCP_SKB_CB(buff)->end_seq = tp->write_seq;
tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
TCP_ECN_send_syn(sk, buff);

/* Send it off. */
TCP_SKB_CB(buff)->when = tcp_time_stamp;
Expand Down Expand Up @@ -2441,15 +2436,9 @@ void tcp_send_ack(struct sock *sk)

/* Reserve space for headers and prepare control bits. */
skb_reserve(buff, MAX_TCP_HEADER);
buff->csum = 0;
TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK;
TCP_SKB_CB(buff)->sacked = 0;
skb_shinfo(buff)->gso_segs = 1;
skb_shinfo(buff)->gso_size = 0;
skb_shinfo(buff)->gso_type = 0;
tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPCB_FLAG_ACK);

/* Send it off, this clears delayed acks for us. */
TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tcp_acceptable_seq(sk);
TCP_SKB_CB(buff)->when = tcp_time_stamp;
tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
}
Expand Down Expand Up @@ -2477,19 +2466,11 @@ static int tcp_xmit_probe_skb(struct sock *sk, int urgent)

/* Reserve space for headers and set control bits. */
skb_reserve(skb, MAX_TCP_HEADER);
skb->csum = 0;
TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
TCP_SKB_CB(skb)->sacked = 0;
skb_shinfo(skb)->gso_segs = 1;
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_type = 0;

/* Use a previous sequence. This should cause the other
* end to send an ack. Don't queue or clone SKB, just
* send it.
*/
TCP_SKB_CB(skb)->seq = tp->snd_una - !urgent;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPCB_FLAG_ACK);
TCP_SKB_CB(skb)->when = tcp_time_stamp;
return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
}
Expand Down

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