[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>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 29d3089..415193e 100644 (file)
--- 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 */

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 6b5c64f..7069327 100644 (file)
--- 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;