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Commit 54287cc1 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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[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: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cf4c6bf8

include/linux/tcp.h

+2 −2
Original line number Diff line number Diff line
@@ -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 */

net/ipv4/tcp_minisocks.c

+2 −4
Original line number Diff line number Diff line
@@ -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;