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

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Date:	Thu, 07 Oct 2010 21:12:03 -0400 (EDT)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Daniel Walker <dwalker@...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, linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/3] [ARM] Translate delay.S into (mostly) C

On Thu, 7 Oct 2010, Stephen Boyd wrote:

> Why doesn't any other architecture use assembly for their lpj code? They
> may use headers with assembly in them or C code with assembly in them,
> but they don't write all of the delay code in assembly and rely on
> function interleaving. This leads me to believe other arches aren't
> concerned about compiler optimizations breaking lpj cmdline parameters,
> so why should ARM be concerned?
> 
> I tested the theory out and scaled down the CPU frequency to 19.2 MHz
> and then called calibrate_delay(). Before and after applying this series
> I got the same results.
> 
> Calibrating delay loop... 12.67 BogoMIPS (lpj=63360)
> 
> Jumping up to 1.2 GHz and calling calibrate_delay() gives me the same
> before and after
> 
> Calibrating delay loop... 792.98 BogoMIPS (lpj=3964928)

OK, fair enough.

> I don't have access to a machine capable of running slower than 19.2
> MHz. Maybe machines running in the KHz range would experience differences?

Don't worry, I doubt any ARM processor capable of running Linux ever was 
that slow.


Nicolas
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