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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Andrew,

On 05/02/2014 04:57 PM, Andrew Cooper wrote:
> On 02/05/14 16:52, Julien Grall wrote:
>> The macro boot_cpu will be used to get CPU variable from the boot CPU.
>>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
>> Suggested-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>> Cc: Keir Fraser <keir@xxxxxxx>
>> ---
>>  xen/include/xen/percpu.h |    3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/xen/include/xen/percpu.h b/xen/include/xen/percpu.h
>> index abe0b11..0e848bf 100644
>> --- 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)
>> +
> 
> What is this actually used for?

I use it to retrieve PPIs (per-processor interrupt) type and initialize
PPIs for the new CPUs.

> In x86 with arbitrary cpu hotplug, we are trying to move away from the
> false assumption than cpu0 is the boot cpu.  Actual boot data is stored
> sideways as boot_$FOO variables, and not accessed with the per-cpu
> mechanism.

My solution won't work for hotplug. As it's not supported for ARM right
now, I think we can live with it.

I can either drop the macro or make ARM specific for now.

Regards,

-- 
Julien Grall

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