mac80211: Change default tx_sk_pacing_shift to 7

tohojo · jmberg-intel · commit 5c14a4d05f68 · 2019-02-22T13:32:55.000+01:00
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 &lt;toke@redhat.com&gt;
Signed-off-by: Johannes Berg &lt;johannes.berg@intel.com&gt;
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
@@ -615,13 +615,13 @@ struct ieee80211_hw *ieee80211_alloc_hw_nm(size_t priv_data_len,
 	 * 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.
 	 * This is the default, anyhow - drivers may need to override it
 	 * for local reasons (longer buffers, longer completion time, or
 	 * similar).
 	 */
-	local->hw.tx_sk_pacing_shift = 8;
+	local->hw.tx_sk_pacing_shift = 7;
 
 	/* set up some defaults */
 	local->hw.queues = 1;
