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

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Date:	Tue, 14 May 2013 19:56:51 -0400 (EDT)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Rob Herring <robherring2@...il.com>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Pavel Machek <pavel@....cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] ARM: delay: print dummy values for bogomips

On Tue, 14 May 2013, Rob Herring wrote:

> On Tue, May 14, 2013 at 2:54 PM, Nicolas Pitre <nico@...xnic.net> wrote:
> > [ Yes, I'm late to the party ]
> >
> > On Tue, 7 May 2013, Marc Zyngier wrote:
> >
> >> On 07/05/13 00:16, Pavel Machek wrote:
> >>
> >> Hi Pawel,
> >>
> >> >> 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
> >>
> >> Removing it would be an ABI breakage. Unfortunately.
> >
> > Did you really write this with a straight face?
> >
> >> Name one userspace application that extracts meaningful information out
> >> of the BogoMIPS field. Just one.
> >
> > Waitaminute... Didn't you just claim this would be an ABI break?
> >
> > So if no application can be found, where is the ABI breakage?
> 
> lscpu
> 
> But that is already "broken" on ARM because x86 uses "bogomips" and
> ARM uses "BogoMIPS". 

So basically it won't be any more broken if the field disappears 
entirely, right?

> I agree reporting BogoMIPS is silly, but there
> are more differences between x86 and ARM. Somewhat meaningful fields
> like "cpu MHz" are missing on ARM for example. These are mainly useful
> for h/w inventory use which server folks tend to care about.

So... the tool must be coping well with missing fields already?  If 
/proc/cpuinfo is missing "important" fields on ARM then this is a 
different issue.

> > This thread must be a joke.  Please just kill the damn thing out of
> > /proc/cpuinfo and see if any application notices.  And if some do then
> > they are already broken *today* and should be fixed.
> 
> And please do so for all arches then.

Why?  It happens that the bogomips reporting on ARM is even more 
"broken" than on other architectures and therefore it deserves to be 
removed even more than on other architectures.  Who knows, maybe it 
still has some semblance of a meaning on those other architectures and 
that should be up to their respective maintainers to decide.


Nicolas
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