linux-kernel - Re: [PATCH 3/3] delay: add generic udelay(), mdelay() and ssleep()

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Message-ID: <20060922093659.GA8609@flint.arm.linux.org.uk>
Date:	Fri, 22 Sep 2006 10:36:59 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Denis Vlasenko <vda.linux@...glemail.com>
Cc:	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH 3/3] delay: add generic udelay(), mdelay() and ssleep()

On Fri, Sep 22, 2006 at 10:00:33AM +0200, Denis Vlasenko wrote:
> * __const_udelay for all arches is removed or renamed to
> ? __const_delay (it did not do microsecond delays anyway)

You never explained this properly - in fact I think your logic is
reversed.  Let me remind you of my reply (which afaics never got
a response):

On Wed, Aug 23, 2006 a 09:14:52AM +0100, Russell King wrote:
> On Wed, Aug 23, 2006 at 07:50:24AM +0200, Denis Vlasenko wrote:
> > On Tuesday 22 August 2006 18:55, Russell King wrote:
> > > Please keep a "const" version in ARM.  Thanks.
> >
> > Are you talking about this hunk? Why do you want to keep it?
> >
> > I mean, without it udelay(n) will become slower by the time
> > needed for one extra multiply. So we will have maybe
> > udelay(n) ==> udelay(n+0.1).
> 
> Why do you think that?  With the constant version, the additional
> unnecessary multiply is optimised away by the compiler (since
> constant * constant = constant), so it's actually slightly faster,
> not sligntly slower as you seem to think.
> 
> Since the multiply is pure overhead, it's better to get rid of it.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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