linux-kernel - Re: [RFC] exponential update_wall

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Message-Id: <1159399221.7297.16.camel@localhost>
Date:	Wed, 27 Sep 2006 16:20:21 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Roman Zippel <zippel@...ux-m68k.org>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] exponential update_wall_time

On Wed, 2006-09-27 at 15:05 -0700, Andrew Morton wrote:
> On Wed, 27 Sep 2006 12:35:33 -0700
> john stultz <johnstul@...ibm.com> wrote:
> 
> > +	while (offset > clock->cycle_interval << (shift + 1))
> > +		shift++;
> 
> hurts my brain.

Yea. Its not the most obvious patch, but the complexity is pretty
isolated.

> I have a vague feeling that this can be done with
> something like ffz(~(offset/clock->cycle_interval))+epsilon, but that hurts
> my brain too.

Agreed. I don't want to obfuscate this code much more. In my opinion,
the loop is tightly bounded and not expensive enough to try to optimize.

thanks
-john


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