linux-kernel - Re: [PATCH] x86, apic: Do not increment disabled_cpus from generic_processor

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Date:	Sun, 09 Jan 2011 21:38:58 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org
Subject: Re: [PATCH] x86, apic: Do not increment disabled_cpus from generic_processor_info.

On 01/09/2011 07:57 PM, Rakib Mullick wrote:
> On Sun, Jan 9, 2011 at 3:39 PM, Ingo Molnar <mingo@...e.hu> wrote:
>>
>> Hm, what effects does this have in practice? smpboot.c uses disabled_cpus as a value
>> to calculate limits - why has this bug not caused some misbehavior somewhere? (or if
>> it has caused misbehavior, what is that?)
> 
> If I'm not wrong, smpboot.c tries to get the possible cpu map by
> calculating disabled_cpus and num_processors. When we pass nr_cpus=n,
> which is less than no. of CPUs available, we can't put more CPUs
> online. So, no of cpu we detect at startup is okay. Or am I missing
> anything?
> 
> thanks,
> rakib
> 

 When nr_cpus=n passed from command line and there is N > n physical cpu
present we *still* have to increment disabled_cpus in generic_processor_info
because:

1) We're priting out the number of cpu which is disabled
2) total_cpus become inconsistent

and while (1) is not that important, total_cpus _is_ important (it
is used to print out offlined cpus).

 So I still fail to see why we need to drop the former increment in
first place.
-- 
    Cyrill
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