Messages in this thread | | | Date | Thu, 26 Jan 2012 22:57:14 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v4 |
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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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