Messages in this thread | | | Date | Mon, 27 Feb 2012 13:55:55 -0800 | From | David Daney <> | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 |
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On 01/31/2012 04:17 PM, 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> > Acked-by: Srivatsa S. Bhat<srivatsa.bhat@linux.vnet.ibm.com> > Acked-by: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
How is it that this patch got merged to linux-next before all the cleanup patches for nr_online_cpus?
From the looks of your follow-on patches it would seem that all MIPS, hexagon, and um are now broken.
I know for a fact that MIPS doesn't boot because of this.
David Daney
> --- > include/linux/cpumask.h | 9 +++++++-- > kernel/cpu.c | 13 +++++++++++++ > 2 files changed, 20 insertions(+), 2 deletions(-) > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index 4f7a632..930e255 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -27,6 +27,9 @@ typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t; > extern int nr_cpu_ids; > #endif > > +extern unsigned int nr_online_cpus; > +extern unsigned int nr_possible_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 +84,10 @@ 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..d520d34 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -604,9 +604,13 @@ EXPORT_SYMBOL(cpu_all_bits); > #ifdef CONFIG_INIT_ALL_POSSIBLE > static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly > = CPU_BITS_ALL; > +unsigned int nr_possible_cpus __read_mostly = CONFIG_NR_CPUS; > #else > static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly; > +unsigned int nr_possible_cpus __read_mostly; > #endif > +EXPORT_SYMBOL(nr_possible_cpus); > + > const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits); > EXPORT_SYMBOL(cpu_possible_mask); > > @@ -614,6 +618,9 @@ static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly; > const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits); > EXPORT_SYMBOL(cpu_online_mask); > > +unsigned int nr_online_cpus __read_mostly; > +EXPORT_SYMBOL(nr_online_cpus); > + > static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly; > const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits); > EXPORT_SYMBOL(cpu_present_mask); > @@ -628,6 +635,8 @@ void set_cpu_possible(unsigned int cpu, bool possible) > cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits)); > else > cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits)); > + > + nr_possible_cpus = cpumask_weight(cpu_possible_mask); > } > > void set_cpu_present(unsigned int cpu, bool present) > @@ -644,6 +653,8 @@ 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) > @@ -662,9 +673,11 @@ void init_cpu_present(const struct cpumask *src) > void init_cpu_possible(const struct cpumask *src) > { > cpumask_copy(to_cpumask(cpu_possible_bits), src); > + nr_possible_cpus = cpumask_weight(cpu_possible_mask); > } > > void init_cpu_online(const struct cpumask *src) > { > cpumask_copy(to_cpumask(cpu_online_bits), src); > + nr_online_cpus = cpumask_weight(cpu_online_mask); > }
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