Re: [PATCH v5 1/8] smp: Introduce a generic on_each_cpu_mask function

[Michal Nazarewicz]

On Tue, 03 Jan 2012 23:26:24 +0100, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon,  2 Jan 2012 12:24:12 +0200
> Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx> 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,  MichaÅ âmina86â Nazarewicz    (o o)
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