mac80211: Change default tx_sk_pacing_shift to 7

commit 5c14a4d0 upstream.

When we did the original tests for the optimal value of sk_pacing_shift, we
came up with 6 ms of buffering as the default. Sadly, 6 is not a power of
two, so when picking the shift value I erred on the size of less buffering
and picked 4 ms instead of 8. This was probably wrong; those 2 ms of extra
buffering makes a larger difference than I thought.

So, change the default pacing shift to 7, which corresponds to 8 ms of
buffering. The point of diminishing returns really kicks in after 8 ms, and
so having this as a default should cut down on the need for extensive
per-device testing and overrides needed in the drivers.

Cc: stable@vger.kernel.org
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/mac80211/tx.c

@@ -3614,10 +3614,10 @@ void __ieee80211_subif_start_xmit(struct sk_buff *skb,
 		/* We need a bit of data queued to build aggregates properly, so
 		 * instruct the TCP stack to allow more than a single ms of data
 		 * to be queued in the stack. The value is a bit-shift of 1
-		 * second, so 8 is ~4ms of queued data. Only affects local TCP
+		 * second, so 7 is ~8ms of queued data. Only affects local TCP
 		 * sockets.
 		 */
-		sk_pacing_shift_update(skb->sk, 8);
+		sk_pacing_shift_update(skb->sk, 7);
 
 		fast_tx = rcu_dereference(sta->fast_tx);