linux-kernel - Re: [PATCH] x86: Issue a warning if number of present CPUs > maxcpus and CONFIG

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Message-ID: <20140217203102.7af3fd28@hananiah.suse.cz>
Date:	Mon, 17 Feb 2014 20:31:02 +0100
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Jan Beulich <JBeulich@...e.com>, Borislav Petkov <bp@...en8.de>,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: Issue a warning if number of present CPUs >
 maxcpus and CONFIG_HOTPLUG=n

On Mon, 17 Feb 2014 16:07:04 -0300
Henrique de Moraes Holschuh <hmh@....eng.br> wrote:

> On Mon, 17 Feb 2014, Petr Tesarik wrote:
> > This results in:
> > 
> >   total_cpus = 1008   /* this is purely informative, it is *NOT* used
> >                          to size anything */
> >   possible = 48       /* clamped to nr_cpu_ids */
> > 
> > A warning message (with or without my patch):
> >   1024 Processors exceeds NR_CPUS limit of 48
> > 
> > Informative message:
> >   Allowing 16 CPUs, 32 hotplug CPUs
> > 
> > No other warning (with or without my patch).
> 
> I'd rather no warnings were printed at all (user asked for that nr_cpus,
> there is no reason to warn him about it),
>[...]

Agreed. This needs some cleanup.

This code used to check against NR_CPUS, which is a compile-time
constant, so the warning was printed when the user booted a kernel
incapable of using all available CPUs in the system. And this was a
good thing, because there was no (easy) way to find out this constant
from a given kernel binary.

I can post a clean-up patch that doesn't issue any warnings for user
overrides (but does issue warnings for exceeding hard-coded kernel
limits).

But I'll do it separately and only after I know if the current patch
gets accepted or not. ;-)

Petr Tesarik
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