linux-kernel - Re: [PATCH 1/3] [ARM] Translate delay.S into (mostly) C

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Date:	Wed, 06 Oct 2010 16:05:25 -0400 (EDT)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Daniel Walker <dwalker@...eaurora.org>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Kevin Hilman <khilman@...prootsystems.com>,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Saravana Kannan <skannan@...eaurora.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Colin Cross <ccross@...roid.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] [ARM] Translate delay.S into (mostly) C

On Wed, 6 Oct 2010, Daniel Walker wrote:

> On Wed, 2010-10-06 at 11:30 -0700, Stephen Boyd wrote:
> > Is there some way to force GCC to do what I want (interleave the
> > functions)? It seems happy to inline them and then optimize the
> > register
> > usage and instruction ordering. Perhaps that is OK though and we're
> > wasting our time trying to be conservative in code size. 

You could use the noinline qualifier from <linux/compiler.h> with those 
functions you don't want inlined.

> Is it possible to do all this in assembly ? Can't you have the default
> implementation using this assembly with different function names, then
> just set the assembly function names in C code someplace?

That weould be my preference too.  Being in assembly means that this 
code is unlikely to change with different optimization levels and/or gcc 
versions which would otherwise require different calibration values. 
Relying on stable calibration is necessary for the lpj kernel cmdline 
parameter to have some meaning.


Nicolas
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