linux-kernel - Re: [PATCH v7 3/3] nl80211/mac80211: Report signal average

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Date:	Fri, 19 Nov 2010 18:07:05 +0900
From:	Bruno Randolf <br1@...fach.org>
To:	Bob Copeland <me@...copeland.com>
Cc:	Johannes Berg <johannes@...solutions.net>, Jouni Malinen <j@...fi>,
	linville@...driver.com, randy.dunlap@...cle.com,
	peterz@...radead.org, blp@...stanford.edu,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lars_Ericsson@...ia.com, stefanr@...6.in-berlin.de,
	kosaki.motohiro@...fujitsu.com, akpm@...ux-foundation.org,
	kevin.granade@...il.com
Subject: Re: [PATCH v7 3/3] nl80211/mac80211: Report signal average

On Thu November 18 2010 08:11:18 Bob Copeland wrote:
> On Wed, Nov 17, 2010 at 11:16 AM, Johannes Berg
> 
> <johannes@...solutions.net> wrote:
> > On Wed, 2010-11-17 at 17:28 +0900, Bruno Randolf wrote:
> >> I understand that this could be more efficient, but if it matters or not
> >> - honestly, I don't know. Can a more knowledgeable person than me
> >> comment on this?
> > 
> > Yes, it does matter -- think of an embedded MIPS board running at 500MHz
> > and trying to push 11n speeds.
> 
> I assume the number of samples (weight) is the more
> important tunable.  One option is you can require factor
> to be a power of two that is much larger than weight,
> then at least you can store factor/weight precomputed
> and multiply by it instead of doing a divide in ewma_add.
> Then ewma_get can also just be a shift as well.

Hmm, maybe I suck in mathemathics, but I don't see a way to do that given the 
formula:

(((internal * (weight - 1)) + (val * factor)) / weight

bruno
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