netdev - [PATCH, take 2] TCP : keep copied_seq, rcv_wup and rcv

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Date:	Thu, 22 Feb 2007 12:11:50 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: [PATCH, take 2] TCP : keep copied_seq, rcv_wup and rcv_next together

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@...mosbay.com>

View attachment "tcp_sock_reorder1.patch" of type "text/plain" (1950 bytes)