The patch titled
Subject: cpumask: avoid mask based num_possible_cpus() and num_online_cpus()
has been added to the -mm tree. Its filename is
cpumask-avoid-mask-based-num_possible_cpus-and-num_online_cpus.patch
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From: Venkatesh Pallipadi <venki@xxxxxxxxxx>
Subject: cpumask: avoid mask based num_possible_cpus() and num_online_cpus()
The kernel's notion of possible cpus (from include/linux/cpumask.h) is
* 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 a 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 at init time (with
only a few runtime calls), it is cleaner to use variables and not go
through this repeated mask based calculation.
Signed-off-by: Venkatesh Pallipadi <venki@xxxxxxxxxx>
Acked-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cpumask.h | 9 +++++++--
kernel/cpu.c | 13 +++++++++++++
2 files changed, 20 insertions(+), 2 deletions(-)
diff -puN include/linux/cpumask.h~cpumask-avoid-mask-based-num_possible_cpus-and-num_online_cpus include/linux/cpumask.h
--- a/include/linux/cpumask.h~cpumask-avoid-mask-based-num_possible_cpus-and-num_online_cpus
+++ a/include/linux/cpumask.h
@@ -27,6 +27,9 @@ typedef struct cpumask { DECLARE_BITMAP(
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_p
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 -puN kernel/cpu.c~cpumask-avoid-mask-based-num_possible_cpus-and-num_online_cpus kernel/cpu.c
--- a/kernel/cpu.c~cpumask-avoid-mask-based-num_possible_cpus-and-num_online_cpus
+++ a/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, C
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,
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, bo
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 cpuma
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);
}
_
Subject: Subject: cpumask: avoid mask based num_possible_cpus() and num_online_cpus()
Patches currently in -mm which might be from venki@xxxxxxxxxx are
cpumask-avoid-mask-based-num_possible_cpus-and-num_online_cpus.patch
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