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SubjectRe: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v4
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@google.com>
> ---


Looks good to me now :-)

Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Regards,
Srivatsa S. Bhat



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