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 <[email protected]>
Cc: Soheil Hassas Yeganeh <[email protected]>
Acked-by: Soheil Hassas Yeganeh <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: edumazet

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)