Message-ID: <527D14B7.3090204@openwrt.org> (sfid-20131108_174340_484461_36E34F6B)
Date: Fri, 08 Nov 2013 17:43:35 +0100
From: Felix Fietkau <nbd@openwrt.org>
MIME-Version: 1.0
To: Karl Beldan <karl.beldan@gmail.com>,
	Johannes Berg <johannes@sipsolutions.net>
CC: linux-wireless <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH 2/2] mac80211: minstrel_ht: do not sample unsupported
 rates
References: <1383928473-798-1-git-send-email-karl.beldan@gmail.com> <1383928473-798-2-git-send-email-karl.beldan@gmail.com>
In-Reply-To: <1383928473-798-2-git-send-email-karl.beldan@gmail.com>
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On 2013-11-08 17:34, Karl Beldan wrote:
> From: Karl Beldan <karl.beldan@rivierawaves.com>
> 
> ATM minstrel_ht does not check whether the sampling rate is supported.
> Unsupported rates attempts can trigger when there are holes between
> supported MCSes belonging to the same group (e.g many devices are
> capable of MCS32 without being capable of MCS33->MCS39).
> This change replaces an unsupported sample index with the fls of the
> bitfield of supported indexes.
> This is not a problem in minstrel which fills a per STA sample table
> with only supported rates (though only at init).
> 
> Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
> ---
>  net/mac80211/rc80211_minstrel_ht.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
> index aeec401..1b835ad 100644
> --- a/net/mac80211/rc80211_minstrel_ht.c
> +++ b/net/mac80211/rc80211_minstrel_ht.c
> @@ -703,6 +703,8 @@ minstrel_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
>  
>  	mg = &mi->groups[mi->sample_group];
>  	sample_idx = sample_table[mg->column][mg->index];
> +	if (!(mg->supported & BIT(sample_idx)))
> +		sample_idx = fls(sample_idx) - 1;
You probably meant fls(mg->supported) - 1 here, however I think a better
approach would be to just skip the sample attempt. If there are fewer
rates in a group, we can run fewer sample attempts on it.

- Felix