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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 <>
    > ---

    Looks good to me now :-)

    Acked-by: Srivatsa S. Bhat <>

    Srivatsa S. Bhat

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