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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.05.14 at 17:58, <julien.grall@xxxxxxxxxx> wrote:
> 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).

Either is fine with me, but putting this in common code isn't.

Jan


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