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

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Date:	Thu, 05 Jan 2012 14:17:54 +0100
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	"Gilad Ben-Yossef" <gilad@...yossef.com>,
	"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 Tue, 03 Jan 2012 23:26:24 +0100, 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.

>> @@ -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.

It may specify none.  For instance, in drain_all_pages() case, if the
CPU has no pages on PCP lists, the mask will be empty and so the
cpumask_test_cpu() will return zero.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--
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