From:   =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     linux-wireless@vger.kernel.org
Cc:     Ben Greear <greearb@candelatech.com>,
        Grant Grundler <grundler@google.com>,
        Kalle Valo <kvalo@codeaurora.org>, wgong@qti.qualcomm.com,
        ath10k@lists.infradead.org, wgong@codeaurora.org,
        Johannes Berg <johannes@sipsolutions.net>,
        Kan Yan <kyan@google.com>,
        =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
Subject: [PATCH] mac80211: Change default tx_sk_pacing_shift to 7
Date:   Thu, 21 Feb 2019 18:29:36 +0100
Message-Id: <20190221172936.21816-1-toke@redhat.com>
In-Reply-To: <87d0nlhxl9.fsf@toke.dk>
References: <87d0nlhxl9.fsf@toke.dk>
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Sender: linux-wireless-owner@vger.kernel.org
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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.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 net/mac80211/main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 5055aeba5c5a..800e67615e2a 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -617,13 +617,13 @@ 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;
-- 
2.20.1