[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, 2 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 29d3089038ab..415193e171e4 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -242,6 +242,8 @@ struct tcp_sock {
  *      See RFC793 and RFC1122. The RFC writes these in capitals.
  */
         u32     rcv_nxt;        /* What we want to receive next         */
+        u32     copied_seq;     /* Head of yet unread data              */
+        u32     rcv_wup;        /* rcv_nxt on last window update sent   */
         u32     snd_nxt;        /* Next sequence we send                */
 
         u32     snd_una;        /* First byte we want an ack for        */
@@ -307,10 +309,8 @@ struct tcp_sock {
         struct sk_buff_head     out_of_order_queue; /* Out of order segments go here */
 
         u32     rcv_wnd;        /* Current receiver window              */
-        u32     rcv_wup;        /* rcv_nxt on last window update sent   */
         u32     write_seq;      /* Tail(+1) of data held in tcp send buffer */
         u32     pushed_seq;     /* Last pushed seq, required to talk to windows */
-        u32     copied_seq;     /* Head of yet unread data              */
 
 /*      SACKs data      */
         struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */