netdev - [PATCH net] tcp: cache line align MAX_TCP

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Date:   Fri, 17 Apr 2020 07:10:23 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: [PATCH net] tcp: cache line align MAX_TCP_HEADER

TCP stack is dumb in how it cooks its output packets.

Depending on MAX_HEADER value, we might chose a bad ending point
for the headers.

If we align the end of TCP headers to cache line boundary, we
make sure to always use the smallest number of cache lines,
which always help.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Soheil Hassas Yeganeh <soheil@...gle.com>
---
 include/net/tcp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5fa9eacd965a4abd6a4dd5262fa0d439aa9fe64e..dcf9a72eeaa6912202e8a1ca6cf800f7401bf517 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -51,7 +51,7 @@ extern struct inet_hashinfo tcp_hashinfo;
 extern struct percpu_counter tcp_orphan_count;
 void tcp_time_wait(struct sock *sk, int state, int timeo);
 
-#define MAX_TCP_HEADER	(128 + MAX_HEADER)
+#define MAX_TCP_HEADER	L1_CACHE_ALIGN(128 + MAX_HEADER)
 #define MAX_TCP_OPTION_SPACE 40
 #define TCP_MIN_SND_MSS		48
 #define TCP_MIN_GSO_SIZE	(TCP_MIN_SND_MSS - MAX_TCP_OPTION_SPACE)
-- 
2.26.1.301.g55bc3eb7cb9-goog