[TCP]: Keep copied_seq, rcv_wup and rcv_next together.

I noticed in oprofile study a cache miss in tcp_rcv_established() to read
copied_seq.

ffffffff80400a80 <tcp_rcv_established>: /* tcp_rcv_established total: 4034293  
2.0400 */

 55493  0.0281 :ffffffff80400bc9:   mov    0x4c8(%r12),%eax copied_seq
543103  0.2746 :ffffffff80400bd1:   cmp    0x3e0(%r12),%eax   rcv_nxt    

if (tp->copied_seq == tp->rcv_nxt &&
        len - tcp_header_len <= tp->ucopy.len) {

In this function, the cache line 0x4c0 -> 0x500 is used only for this
reading 'copied_seq' field.

rcv_wup and copied_seq should be next to rcv_nxt field, to lower number of
active cache lines in hot paths. (tcp_rcv_established(), tcp_poll(), ...)

As you suggested, I changed tcp_create_openreq_child() so that these fields
are changed together, to avoid adding a new store buffer stall.

Patch is 64bit friendly (no new hole because of alignment constraints)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 4 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 6b5c64f3c92..706932726a1 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -387,8 +387,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 /* Now setup tcp_sock */
                 newtp = tcp_sk(newsk);
                 newtp->pred_flags = 0;
-                newtp->rcv_nxt = treq->rcv_isn + 1;
-                newtp->snd_nxt = newtp->snd_una = newtp->snd_sml = treq->snt_isn + 1;
+                newtp->rcv_wup = newtp->copied_seq = newtp->rcv_nxt = treq->rcv_isn + 1;
+                newtp->snd_sml = newtp->snd_una = newtp->snd_nxt = treq->snt_isn + 1;
 
                 tcp_prequeue_init(newtp);
 
@@ -422,10 +422,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 tcp_set_ca_state(newsk, TCP_CA_Open);
                 tcp_init_xmit_timers(newsk);
                 skb_queue_head_init(&newtp->out_of_order_queue);
-                newtp->rcv_wup = treq->rcv_isn + 1;
                 newtp->write_seq = treq->snt_isn + 1;
                 newtp->pushed_seq = newtp->write_seq;
-                newtp->copied_seq = treq->rcv_isn + 1;
 
                 newtp->rx_opt.saw_tstamp = 0;