linux-kernel - Re: [PATCH 09/10] x86: oprofile: remove NR_CPUS arrays in arch/x86/oprofile/nmi

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Date:	Wed, 26 Mar 2008 07:53:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Philippe Elie <phil.el@...adoo.fr>
Subject: Re: [PATCH 09/10] x86: oprofile: remove NR_CPUS arrays in
	arch/x86/oprofile/nmi_int.c


* Mike Travis <travis@....com> wrote:

> Change the following arrays sized by NR_CPUS to be PERCPU variables:
> 
> 	static struct op_msrs cpu_msrs[NR_CPUS];
> 	static unsigned long saved_lvtpc[NR_CPUS];
> 
> Also some minor complaints from checkpatch.pl fixed.

thanks, applied.

> All changes were transparent except for:
> 
>  static void nmi_shutdown(void)
>  {
> +	struct op_msrs *msrs = &__get_cpu_var(cpu_msrs);
>  	nmi_enabled = 0;
>  	on_each_cpu(nmi_cpu_shutdown, NULL, 0, 1);
>  	unregister_die_notifier(&profile_exceptions_nb);
> -	model->shutdown(cpu_msrs);
> +	model->shutdown(msrs);
>  	free_msrs();
>  }
> 
> The existing code passed a reference to cpu 0's instance of struct 
> op_msrs to model->shutdown, whilst the other functions are passed a 
> reference to <this cpu's> instance of a struct op_msrs.  This seemed 
> to be a bug to me even though as long as cpu 0 and <this cpu> are of 
> the same type it would have the same effect...?

i dont think this has any real effect in practice (the model pointers 
are not expected to change across cpus on the same system) - but in any 
case i've promoted your observation to the main portion of the changelog 
so that we'll have notice of this.

(someone might want to play with simulating a weaker CPU on a secondary 
core, but we've got tons of other assumptions on CPU type symmetry.)

	Ingo
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