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Message-ID: <f40bd542d0d13f5be701de41b8870b0bd1f34230.camel@sipsolutions.net>
Subject: Re: [PATCH 2/2] mac80211: minstrel_ht: replace rate stats ewma with
 a better moving average
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Felix Fietkau <nbd@nbd.name>, linux-wireless@vger.kernel.org
Date:   Tue, 01 Oct 2019 12:17:36 +0200
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> This change replaces the EWMA implementation with a moving average that's
> designed to significantly reduce lag while keeping a bigger window size
> by being better at filtering out noise.
> 
> It is only slightly more expensive than the simple EWMA and still avoids
> divisions in its calculation.
> 
> The algorithm is adapted from an implementation intended for a completely
> different field (stock market trading), where the tradeoff of lag vs
> noise filtering is equally important. It is based on the "smoothing filter"
> from http://www.stockspotter.com/files/PredictiveIndicators.pdf.
> 
> I have adapted it to fixed-point math with some constants so that it uses
> only addition, bit shifts and multiplication
> 

Would it be worth pulling that out into similar helpers to EWMA in
average.h, perhaps even in the same file?

You need to keep a bit more state, but essentially the same API should
work since EWMA already declares the "struct ewma_something" once you
use the DECLARE_EWMA().

johannes