Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v4

[KOSAKI Motohiro]

2012/1/26 Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>:
> On 01/25/2012 04:55 AM, Venkatesh Pallipadi wrote:
>
>> Kernel's notion of possible cpus (from include/linux/cpumask.h)
>>  *     cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
>>
>>  *  The cpu_possible_mask is fixed at boot time, as the set of CPU id's
>>  *  that it is possible might ever be plugged in at anytime during the
>>  *  life of that system boot.
>>
>>  #define num_possible_cpus()     cpumask_weight(cpu_possible_mask)
>>
>> and on x86 cpumask_weight() calls hweight64 and hweight64 (on older kernels
>> and systems with !X86_FEATURE_POPCNT) or a popcnt based alternative.
>>
>> i.e, We needlessly go through this mask based calculation everytime
>> num_possible_cpus() is called.
>>
>> The problem is there with cpu_online_mask() as well, which is fixed value at
>> boot time in !CONFIG_HOTPLUG_CPU case and should not change that often even
>> in HOTPLUG case.
>>
>> Though most of the callers of these two routines are init time (with few
>> exceptions of runtime calls), it is cleaner to use variables
>> and not go through this repeated mask based calculation.
>>
>> Signed-off-by: Venkatesh Pallipadi <venki@xxxxxxxxxx>
>> ---
>
>
> Looks good to me now :-)
>
> Acked-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>

I'm ok too.

Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
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