[PATCH 4.19 04/78] mac80211: Change default tx_sk_pacing_shift to 7

From: Greg Kroah-Hartman
Date: Mon Mar 04 2019 - 03:28:27 EST

4.19-stable review patch. If anyone has any objections, please let me know.


From: Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx>

commit 5c14a4d05f68415af9e41a4e667d1748d41d1baf 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@xxxxxxxxxxxxxxx
Signed-off-by: Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/mac80211/tx.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3614,10 +3614,10 @@ void __ieee80211_subif_start_xmit(struct
/* 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);