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

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Message-ID: <CAOtvUMcx0etVbYWz_z66ns9NbU=rvRChQqc1YYYYNJjYmOUsoQ@mail.gmail.com>
Date:	Sun, 8 Jan 2012 18:04:19 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 Wed, Jan 4, 2012 at 12:26 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> 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.

As Michal already answered, because the current CPU might be not
specified in the mask, even on UP.

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

Comment added and will be included in V6.

Thanks for the review.

Gilad



-- 
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@...yossef.com
Israel Cell: +972-52-8260388
US Cell: +1-973-8260388
http://benyossef.com

"Unfortunately, cache misses are an equal opportunity pain provider."
-- Mike Galbraith, LKML
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