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Date:   Fri, 21 Apr 2023 13:51:06 +0200
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Subject: Re: [PATCH v1] wifi: mac80211: Initialize EWMA fail avg to 1
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To:     Johannes Berg <johannes@sipsolutions.net>,
        Felix Fietkau <nbd@nbd.name>
CC:     Karthik M <quic_karm@quicinc.com>,
        <linux-wireless@vger.kernel.org>,
        Tamizh Chelvam Raja <quic_tamizhr@quicinc.com>
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From:   Benjamin Beichler <Benjamin.Beichler@uni-rostock.de>
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Am 21.04.2023 um 13:13 schrieb Johannes Berg:
> =5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=
=5F=5F=5F=5F=5F=5F=5F
>   Achtung! Externe E-Mail: Klicken Sie erst dann auf Links und Anh=C3=A4nge,=
 nachdem Sie die Vertrauensw=C3=BCrdigkeit der Absenderadresse gepr=C3=BCft ha=
ben.
> =5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=
=5F=5F=5F=5F=5F=5F=5F
>
> On Fri, 2023-04-21 at 12:34 +0200, Benjamin Beichler wrote:
>>>> So then let's say we want to fix the existing code. I can think of these
>>>> possible ways:
>>>>
>>>>    * splitting off a bit for initialized from the unsigned long
>>>>      (which at least for 64-bit should be OK since presumably most code
>>>>       using this will run on 32-bit systems too)
>>>>    * adding another value for it, e.g. making it u32 and adding a bool
>>>> for
>>>>      "first value"
>>>>    * biasing the value, like Felix proposes, could be by 1 or -1 for
>>>>      example
>> You forgot the possibility to introduce a separate init function, which
>> boils down to a shift with an assignment statement for code, and no
>> further data memory cost. Even simply extending the current init
>> function (which simply always set 0) would be enough.
> Sort of. Yeah I should've mentioned it, but that means you actually have
> to know the first value, and track "first time usage" separately in the
> user code.
>
> Or you init to something useful at the first value, e.g. saying for
> signal strength "let's assume -45dBm average if we don't know". That
> doesn't seem very practical=3F
I think (at least for the usages I dig into), either those values are 
already defined and applied with a bogus *=5Fadd.
>
> The behaviour of "first value inserted will init" seems sensible.

Okay, my suggestion, as this is a c-macro version, which is generated 
for each user: why not offer both=3F If it is unused, the compiler will 
sort that out. Then we simply keep the zero as special value for init 
(and document it) and otherwise for the more mathematically defined 
usage. But my feeling is, that most users do not care about the first 
values that much and wait to let the ewma settle to some value.

I try to do a RFC patch, with what I mean.


Benjamin