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

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Message-Id: <201011121044.40274.br1@einfach.org>
Date:	Fri, 12 Nov 2010 10:44:40 +0900
From:	Bruno Randolf <br1@...fach.org>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	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,
	kosaki.motohiro@...fujitsu.com, kevin.granade@...il.com,
	"John W. Linville" <linville@...driver.com>
Subject: Re: [PATCH v6] Add generic exponentially weighted moving average (EWMA) function

On Fri November 12 2010 03:17:34 Stefan Richter wrote:
> It seems totally clear-cut to me that code like this is submitted together
> with at least one call site, and it is submitted through the tree in which
> that call site is maintained.

Ok. So I'll re-send the patch thru John's wireless tree after I fixed up your 
comments.

> >> (And it's a bit sad that the function will exist in the base vmlinux
> >> even for people who don't ever use it, but that's a problem which we
> >> don't really have a good solution for).
> > 
> > Hmm, should I switch it back to all inlines?
> 
> Add a hidden Kconfig variable for it which is SELECTed by those Kconfig
> prompts that require it?  That's the good solution that we use for a number
> of similar library functions.
> $ cat lib/Makefile

Ok.

> You use WARN_ON in lib/average.c.  You should include <linux/bug.h>.

Thanks.

> 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));

Bruno
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