linux-kernel - Re: [PATCH v5 1/8] smp: Introduce a generic on_each_cpu

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Date:	Tue, 3 Jan 2012 14:26:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
Cc:	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>, Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Sasha Levin <levinsasha928@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v5 1/8] smp: Introduce a generic on_each_cpu_mask
 function

On Mon,  2 Jan 2012 12:24:12 +0200
Gilad Ben-Yossef <gilad@...yossef.com> wrote:

> on_each_cpu_mask calls a function on processors specified my cpumask,
> which may include the local processor.
> 
> All the limitation specified in smp_call_function_many apply.
> 
> ...
>
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -102,6 +102,13 @@ static inline void call_function_init(void) { }
>  int on_each_cpu(smp_call_func_t func, void *info, int wait);
>  
>  /*
> + * Call a function on processors specified by mask, which might include
> + * the local one.
> + */
> +void on_each_cpu_mask(const struct cpumask *mask, void (*func)(void *),
> +		void *info, bool wait);
> +
> +/*
>   * Mark the boot cpu "online" so that it can call console drivers in
>   * printk() and can access its per-cpu storage.
>   */
> @@ -132,6 +139,15 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info)
>  		local_irq_enable();		\
>  		0;				\
>  	})
> +#define on_each_cpu_mask(mask, func, info, wait) \
> +	do {						\
> +		if (cpumask_test_cpu(0, (mask))) {	\
> +			local_irq_disable();		\
> +			(func)(info);			\
> +			local_irq_enable();		\
> +		}					\
> +	} while (0)

Why is the cpumask_test_cpu() call there?  It's hard to think of a
reason why "mask" would specify any CPU other than "0" in a
uniprocessor kernel.

If this code remains as-is, please add a comment here explaining this,
so others don't wonder the same thing.


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