Messages in this thread | | | Date | Fri, 20 Jan 2012 02:13:11 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus |
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Hi,
On 01/20/2012 01:31 AM, Venkatesh Pallipadi wrote:
> Does this look better? Will send separate patch to fix code > using num_possible_cpus() when they actually need nr_cpu_ids. > > > > 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> > --- > include/linux/cpumask.h | 10 ++++++++-- > kernel/cpu.c | 5 +++++ > kernel/smp.c | 4 ++++ > 3 files changed, 17 insertions(+), 2 deletions(-) > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index 4f7a632..ac3113b 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -23,10 +23,14 @@ typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t; > > #if NR_CPUS == 1 > #define nr_cpu_ids 1 > +#define nr_possible_cpus 1 > #else > extern int nr_cpu_ids; > +extern int nr_possible_cpus; > #endif > > +extern int nr_online_cpus; > + > #ifdef CONFIG_CPUMASK_OFFSTACK > /* Assuming NR_CPUS is huge, a runtime limit is more efficient. Also, > * not all bits may be allocated. */ > @@ -81,8 +85,10 @@ extern const struct cpumask *const cpu_present_mask; > extern const struct cpumask *const cpu_active_mask; > > #if NR_CPUS > 1 > -#define num_online_cpus() cpumask_weight(cpu_online_mask) > -#define num_possible_cpus() cpumask_weight(cpu_possible_mask) > + > +#define num_online_cpus() (nr_online_cpus) > +#define num_possible_cpus() (nr_possible_cpus) > + > #define num_present_cpus() cpumask_weight(cpu_present_mask) > #define num_active_cpus() cpumask_weight(cpu_active_mask) > #define cpu_online(cpu) cpumask_test_cpu((cpu), cpu_online_mask) > diff --git a/kernel/cpu.c b/kernel/cpu.c > index 2060c6e..f179baa 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -622,6 +622,9 @@ static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly; > const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits); > EXPORT_SYMBOL(cpu_active_mask); > > +int nr_online_cpus __read_mostly; > +EXPORT_SYMBOL(nr_online_cpus); > + > void set_cpu_possible(unsigned int cpu, bool possible) > { > if (possible)
Did you forget to add:
nr_possible_cpus = cpumask_weight(cpu_possible_mask);
inside set_cpu_possible() ?
> @@ -644,6 +647,8 @@ void set_cpu_online(unsigned int cpu, bool online) > cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits)); > else > cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits)); > + > + nr_online_cpus = cpumask_weight(cpu_online_mask); > } > > void set_cpu_active(unsigned int cpu, bool active) > diff --git a/kernel/smp.c b/kernel/smp.c > index db197d6..106e519 100644 > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -658,10 +658,14 @@ early_param("maxcpus", maxcpus); > int nr_cpu_ids __read_mostly = NR_CPUS; > EXPORT_SYMBOL(nr_cpu_ids); > > +int nr_possible_cpus __read_mostly = NR_CPUS; > +EXPORT_SYMBOL(nr_possible_cpus); > + > /* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */ > void __init setup_nr_cpu_ids(void) > { > nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1; > + nr_possible_cpus = cpumask_weight(cpu_possible_mask); > } > > /* Called by boot processor to activate the rest. */
Regards, Srivatsa S. Bhat
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