Re: [Xen-devel] [PATCH v5 1/6] xen: Add convenient macro boot_cpu

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 05/05/2014 08:59 AM, Jan Beulich wrote:
>>>> On 02.05.14 at 17:52, <julien.grall@xxxxxxxxxx> wrote:
>> --- a/xen/include/xen/percpu.h
>> +++ b/xen/include/xen/percpu.h
>> @@ -16,6 +16,9 @@
>>  /* Preferred on Xen. Also see arch-defined per_cpu(). */
>>  #define this_cpu(var)    __get_cpu_var(var)
>>  
>> +/* Access variable on boot CPU */
>> +#define boot_cpu(var)   per_cpu(var, 0)
>> +
>>  /* Linux compatibility. */
>>  #define get_cpu_var(var) this_cpu(var)
>>  #define put_cpu_var(var)
> 
> I can only second Andrew's comment - without it becoming clear when
> and why this would be used, this isn't going to be acceptable (and if
> it really was correct and worthwhile, this small a change wouldn't need
> separating out from the code that's intended to actually make use of it).

It's used in the next patch (ie #2). I thought it was better to move out
this small change rather than introducing it in the patch.

This macro is here for a shortcut of per_cpu(myvar, 0). We have few
usage on ARM, most of them are during boot.

There is another when a secondary CPUs is booting. We need to retrieve
the PPIs type (level/edge...) from the boot CPU.

As said in the answer to Andrew, I can either move this macro in an ARM
specific header or open code per_cpu(...,0).

Regards,

-- 
Julien Grall

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