Re: [PATCH] percpu data: only iterate over possible CPUs

[Eric Dumazet <dada1@cosmosbay.com>]

Heiko Carstens a écrit :
>>>>>  > Actually, x86 appears to be the only arch which suffers this braindamage. 
>>>>>  > The rest use CPU_MASK_NONE (or just forget to initialise it and hope that
>>>>>  > CPU_MASK_NONE equals all-zeroes).
>>>>>
>>>>>  s390 will join, as soon as the cpu_possible_map fix is merged...
>>>> What cpu_possible_map fix?
>>> This one:
>>>
>>> http://lkml.org/lkml/2006/2/8/162
>>>
>> Oh, OK.  Ow, I don't think you want to do that.  It means that all those
>> for_each_cpu() loops will now be iterating over all NR_CPUS cpus, whether
>> or not they're even possible.
> 
> That's ok. We're mainly running under z/VM where you can attach new virtual
> cpus on the fly to the virtual machine (up to 64 cpus).
> The only difference to before is that it was possible to limit the waste of
> resources by passing a number with 'maxcpus'. This value was used to generate
> the cpu_possible_map.
> But since the map needs to be ready when we return from setup_arch, we don't
> have access to max_cpus, unless we parse commandline on our own...
> 

Then it's OK to clear bits from cpu_possible_map once you have max_cpus value

for (cpu = max_cpus ; cpu < NR_CPUS ; cpu++)
	cpu_clear(cpu, cpu_possible_map);