[PATCH, take 2] TCP : keep copied_seq, rcv_wup and rcv_next together

[Eric Dumazet <dada1@cosmosbay.com>]

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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(), ...)

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>

[-- Attachment #2: tcp_sock_reorder1.patch --]
[-- Type: text/plain, Size: 1949 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 */
--- linux/net/ipv4/tcp_minisocks.c	2007-02-22 12:41:26.000000000 +0100
+++ linux-ed/net/ipv4/tcp_minisocks.c	2007-02-22 12:49:49.000000000 +0100
@@ -387,8 +387,8 @@ struct sock *tcp_create_openreq_child(st
 		/* 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(st
 		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;