[PATCH] TCP : keep copied_seq, rcv_wup and rcv_next together

[Eric Dumazet <dada1@cosmosbay.com>]

[-- Attachment #1: Type: text/plain, Size: 790 bytes --]

Hi David

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(), ...)

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

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

[-- Attachment #2: tcp_sock_reorder1.patch --]
[-- Type: text/plain, Size: 982 bytes --]

--- linux/include/linux/tcp.h	2007-02-22 11:53:22.000000000 +0100
+++ linux-ed/include/linux/tcp.h	2007-02-22 12:03:19.000000000 +0100
@@ -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 */