linux-kernel - Re: [RFC PATCH 1/2] ARM: delay: print dummy values for bogomips

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Message-ID: <20130506231554.GB16801@amd.pavel.ucw.cz>
Date:	Tue, 7 May 2013 01:16:14 +0200
From:	Pavel Machek <pavel@....cz>
To:	Will Deacon <will.deacon@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] ARM: delay: print dummy values for bogomips

Hi!

> Now that we support a timer-backed delay loop, I'm quickly getting sick
> and tired of people complaining that their beloved bogomips value has
> decreased. You know who you are!

> Unfortunately, we can't just remove the entry from /proc/cpuinfo, as it
> will likely break fragile userspace code which is parsing that stuff, so
> instead replace it with a dummy value that can be chosen in the
> Kconfig.

So, instead of removing it you silently report invalid value? Note
that there's no cpumhz display in procinfo... at least on OLPC I
looked.

And whether it is 30MHz or 3GHz cpu might be relevant information for
userspace, and yes, bogomips used to be good enough for that.

Actually it was mhz, mhz/2 or mhz*2 on pretty much all reasonable systems.

> +choice
> +	prompt "BogoMIPs setting"
> +	default BOGOMIPS_MEDIUM
> +	help
> +	  The BogoMIPs value reported by Linux is exactly what it sounds
> +	  like: totally bogus. It is used to calibrate the delay loop,
> +	  which may be backed by a timer clocked completely independently
> +	  of the CPU.

This is too ugly to live, sorry.

> +	config BOGOMIPS_SLOW
> +		bool "Slow (older machines)"
> +		help
> +		  If you're comparing a faster machine with a slower machine,
> +		  then you might want this option selected on one of them.
> +
> +	config BOGOMIPS_MEDIUM
> +		bool "Medium (default)"
> +		help
> +		  A BogoMIPS value for the masses.
> +
> +	config BOGOMIPS_FAST
> +		bool "Fast (marketing)"
> +		help
> +		  Some people believe that software runs faster with this
> +		  setting so, if you're one of them, say Y here.

April 1st came late this year?

									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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