[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/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 6b5c64f..7069327 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -387,8 +387,8 @@
/* 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 @@
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;