Return-path: Received: from mail-ey0-f174.google.com ([209.85.215.174]:45528 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753679Ab0GZRK5 convert rfc822-to-8bit (ORCPT ); Mon, 26 Jul 2010 13:10:57 -0400 Received: by eya25 with SMTP id 25so520898eya.19 for ; Mon, 26 Jul 2010 10:10:56 -0700 (PDT) MIME-Version: 1.0 Date: Mon, 26 Jul 2010 19:10:55 +0200 Message-ID: Subject: [RFC] ath9k: improve aggregation throughput by using only first rate From: =?ISO-8859-1?Q?Bj=F6rn_Smedman?= To: ath9k-devel@lists.ath9k.org, linux-wireless Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi all, I've been running a lot of iperf on AR913x / compat-wireless-2010-07-16 (w/ openwrt/trunk@22388). I think there are some (in theory) simple improvements that can be done to the tx aggregation / rate control logic. A proof of concept of one such improvement is provided below. Basically, it's a hack that makes ath9k output aggregates with only the first rate in the rate series. The reasoning is that a failure is not a problem for aggregates because there is software retry. Retrying in hardware at a slower rate is counter productive. So, better to fail and do a software retry at possibly another rate. Also, since the aggregate size is often limited by the slowest rate in the MRR series (4 ms txop limit) having a slow rate in the series may affect performance even if it is never used by the hardware. In my (not so scientific) tests max AP downstream throughput increases about 30-40% with the patch below (from 33.9 to 55.7 Mbit/s with HT20 in noisy environment with 20 meters and a few walls between AP and client). Of course, if all rates in the series are high then this patch has no effect. /Bj?rn --- diff -urpN a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c --- a/drivers/net/wireless/ath/ath9k/xmit.c 2010-07-26 15:35:17.000000000 +0200 +++ b/drivers/net/wireless/ath/ath9k/xmit.c 2010-07-26 17:11:33.000000000 +0200 @@ -565,7 +565,7 @@ static u32 ath_lookup_rate(struct ath_so */ max_4ms_framelen = ATH_AMPDU_LIMIT_MAX; - for (i = 0; i < 4; i++) { + for (i = 0; i < 1; i++) { if (rates[i].count) { int modeidx; if (!(rates[i].flags & IEEE80211_TX_RC_MCS)) { @@ -1553,6 +1553,9 @@ static void ath_buf_set_rate(struct ath_ if (sc->sc_flags & SC_OP_PREAMBLE_SHORT) ctsrate |= rate->hw_value_short; + if (bf_isaggr(bf)) + rates[1].count = rates[2].count = rates[3].count = 0; + for (i = 0; i < 4; i++) { bool is_40, is_sgi, is_sp; int phy;