mac80211: Change default tx_sk_pacing_shift to 7

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>

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 87a7299267340675be3bd910183bdd84471deeaf..977dea436ee89dda59c4ba8e3e03114759dca323 100644 (file)
--- 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;