linux-kernel - Re: [PATCH v6] Add generic exponentially weighted moving average (EWMA) function

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Message-Id: <201011151110.46007.br1@einfach.org>
Date:	Mon, 15 Nov 2010 11:10:45 +0900
From:	Bruno Randolf <br1@...fach.org>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	randy.dunlap@...cle.com, peterz@...radead.org, blp@...stanford.edu,
	linux-kernel@...r.kernel.org, Lars_Ericsson@...ia.com,
	kevin.granade@...il.com,
	"John W. Linville" <linville@...driver.com>
Subject: Re: [PATCH v6] Add generic exponentially weighted moving average (EWMA) function

On Sun November 14 2010 17:51:08 Stefan Richter wrote:
> >>> Why do ewma_init() and ewma_add() return their first argument?  They
> >>> look to me like they can be straight-forward void functions.
> >> 
> >> You are right, for ewma_init() it does not make sense.
> >> 
> >> For ewma_add() I think it does. This has been discussed before (e.g.
> >> http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-10/msg09124.html).
> >> Some people might want to get the value when they add a sample by using
> >> ewma_get(ewma_add(&ewma, val));
> >> 
> > 	ewma_add(&ewma, val);
> > 	ewma_get(&ewma);
> > 
> > is enough simpler and cleaner. I don't oppse this :)
> 
> There are more candidate colors for the bike shed: :-)
>   - an ewma_add_return could do what ewma_get(ewma_add(...)) is meant for,

I think this would be overkill. We're just talking about a return pointer...

>   - or ewma_add itself could return the result.

The way I intend to use it, I will add samples much more often than I get a 
value, so IMHO it makes sense to split it.

> BTW, isn't "get" more usually used as a prefix for these kinds of functions
> in kernel APIs?  "get" as a suffix more often means "get a reference"
> alias increase reference count rather than "get the value".

Umm. I don't know and honstly I don't care. I think the API ewma_* is 
consistent. If you have a good reason to change it please let me know, 
otherwise i'd just leave it like it is now.

bruno
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