From: Felix Fietkau <nbd@nbd.name>
To: Johannes Berg <johannes@sipsolutions.net>,
linux-wireless@vger.kernel.org
Subject: Re: [PATCH 2/2] mac80211: minstrel_ht: replace rate stats ewma with a better moving average
Date: Tue, 1 Oct 2019 12:52:13 +0200 [thread overview]
Message-ID: <017c1a59-edf2-0a1a-aa8c-3c32e57d6cd0@nbd.name> (raw)
In-Reply-To: <f40bd542d0d13f5be701de41b8870b0bd1f34230.camel@sipsolutions.net>
On 2019-10-01 12:17, Johannes Berg wrote:
>
>> 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().
Might be useful, yes. The main issue here is that the period / window
size has to be hardcoded through the coefficient values, unless we find
a way to do floating point math, including exp() and cos() at compile
time, including conversion to fixed point.
- Felix
next prev parent reply other threads:[~2019-10-01 10:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-29 15:46 [PATCH 1/2] mac80211: minstrel: remove divisions in tx status path Felix Fietkau
2019-09-29 15:46 ` [PATCH 2/2] mac80211: minstrel_ht: replace rate stats ewma with a better moving average Felix Fietkau
2019-09-29 18:42 ` Toke Høiland-Jørgensen
2019-09-29 19:18 ` Felix Fietkau
2019-09-29 19:46 ` Toke Høiland-Jørgensen
2019-10-01 10:17 ` Johannes Berg
2019-10-01 10:52 ` Felix Fietkau [this message]
2019-10-01 11:06 ` Johannes Berg
2019-10-01 11:11 ` Johannes Berg
2019-10-08 9:18 ` Koen Vandeputte
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