* Increase performance for systems with large count NR_CPUS by limiting
the range of the cpumask operators that loop over the bits in a cpumask_t
variable. This removes a large amount of wasted cpu cycles.
* Add performance variants of the cpumask operators:
int cpus_weight_nr(mask) Same using nr_cpu_ids instead of NR_CPUS
int first_cpu_nr(mask) Number lowest set bit, or nr_cpu_ids
int next_cpu_nr(cpu, mask) Next cpu past 'cpu', or nr_cpu_ids
for_each_cpu_mask_nr(cpu, mask) for-loop cpu over mask using nr_cpu_ids
* Modify following to use performance variants:
#define num_online_cpus() cpus_weight_nr(cpu_online_map)
#define num_possible_cpus() cpus_weight_nr(cpu_possible_map)
#define num_present_cpus() cpus_weight_nr(cpu_present_map)
#define for_each_possible_cpu(cpu) for_each_cpu_mask_nr((cpu), ...)
#define for_each_online_cpu(cpu) for_each_cpu_mask_nr((cpu), ...)
#define for_each_present_cpu(cpu) for_each_cpu_mask_nr((cpu), ...)
* Comment added to include/linux/cpumask.h:
Note: The alternate operations with the suffix "_nr" are used
to limit the range of the loop to nr_cpu_ids instead of
NR_CPUS when NR_CPUS > 64 for performance reasons.
If NR_CPUS is <= 64 then most assembler bitmask
operators execute faster with a constant range, so
the operator will continue to use NR_CPUS.
Another consideration is that nr_cpu_ids is initialized
to NR_CPUS and isn't lowered until the possible cpus are
discovered (including any disabled cpus). So early uses
will span the entire range of NR_CPUS.
(The net effect is that for systems with 64 or less CPU's there are no
functional changes.)
For inclusion into sched-devel/latest tree.
Based on:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
+ sched-devel/latest .../mingo/linux-2.6-sched-devel.git
Cc: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Reviewed-by: Paul Jackson <pj@sgi.com>
Reviewed-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
---
include/linux/cpumask.h | 92 ++++++++++++++++++++++++++++++++----------------
lib/cpumask.c | 9 ++++
2 files changed, 71 insertions(+), 30 deletions(-)
--- linux-2.6.sched.orig/include/linux/cpumask.h
+++ linux-2.6.sched/include/linux/cpumask.h
@@ -15,6 +15,20 @@
* For details of cpu_remap(), see bitmap_bitremap in lib/bitmap.c
* For details of cpus_remap(), see bitmap_remap in lib/bitmap.c.
*
+ * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+ * Note: The alternate operations with the suffix "_nr" are used
+ * to limit the range of the loop to nr_cpu_ids instead of
+ * NR_CPUS when NR_CPUS > 64 for performance reasons.
+ * If NR_CPUS is <= 64 then most assembler bitmask
+ * operators execute faster with a constant range, so
+ * the operator will continue to use NR_CPUS.
+ *
+ * Another consideration is that nr_cpu_ids is initialized
+ * to NR_CPUS and isn't lowered until the possible cpus are
+ * discovered (including any disabled cpus). So early uses
+ * will span the entire range of NR_CPUS.
+ * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+ *
* The available cpumask operations are:
*
* void cpu_set(cpu, mask) turn on bit 'cpu' in mask
@@ -36,12 +50,14 @@
* int cpus_empty(mask) Is mask empty (no bits sets)?
* int cpus_full(mask) Is mask full (all bits sets)?
* int cpus_weight(mask) Hamming weigh - number of set bits
+ * int cpus_weight_nr(mask) Same using nr_cpu_ids instead of NR_CPUS
*
* void cpus_shift_right(dst, src, n) Shift right
* void cpus_shift_left(dst, src, n) Shift left
*
* int first_cpu(mask) Number lowest set bit, or NR_CPUS
* int next_cpu(cpu, mask) Next cpu past 'cpu', or NR_CPUS
+ * int next_cpu_nr(cpu, mask) Next cpu past 'cpu', or nr_cpu_ids
*
* cpumask_t cpumask_of_cpu(cpu) Return cpumask with bit 'cpu' set
* CPU_MASK_ALL Initializer - all bits set
@@ -55,7 +71,8 @@
* int cpu_remap(oldbit, old, new) newbit = map(old, new)(oldbit)
* int cpus_remap(dst, src, old, new) *dst = map(old, new)(src)
*
- * for_each_cpu_mask(cpu, mask) for-loop cpu over mask
+ * for_each_cpu_mask(cpu, mask) for-loop cpu over mask using NR_CPUS
+ * for_each_cpu_mask_nr(cpu, mask) for-loop cpu over mask using nr_cpu_ids
*
* int num_online_cpus() Number of online CPUs
* int num_possible_cpus() Number of all possible CPUs
@@ -212,15 +229,6 @@ static inline void __cpus_shift_left(cpu
bitmap_shift_left(dstp->bits, srcp->bits, n, nbits);
}
-#ifdef CONFIG_SMP
-int __first_cpu(const cpumask_t *srcp);
-#define first_cpu(src) __first_cpu(&(src))
-int __next_cpu(int n, const cpumask_t *srcp);
-#define next_cpu(n, src) __next_cpu((n), &(src))
-#else
-#define first_cpu(src) ({ (void)(src); 0; })
-#define next_cpu(n, src) ({ (void)(src); 1; })
-#endif
#ifdef CONFIG_HAVE_CPUMASK_OF_CPU_MAP
extern cpumask_t *cpumask_of_cpu_map;
@@ -330,15 +338,48 @@ static inline void __cpus_remap(cpumask_
bitmap_remap(dstp->bits, srcp->bits, oldp->bits, newp->bits, nbits);
}
-#if NR_CPUS > 1
+#if NR_CPUS == 1
+
+#define nr_cpu_ids 1
+#define first_cpu(src) ({ (void)(src); 0; })
+#define next_cpu(n, src) ({ (void)(src); 1; })
+#define any_online_cpu(mask) 0
+#define for_each_cpu_mask(cpu, mask) \
+ for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)
+
+#else /* NR_CPUS > 1 */
+
+extern int nr_cpu_ids;
+int __first_cpu(const cpumask_t *srcp);
+int __next_cpu(int n, const cpumask_t *srcp);
+int __any_online_cpu(const cpumask_t *mask);
+
+#define first_cpu(src) __first_cpu(&(src))
+#define next_cpu(n, src) __next_cpu((n), &(src))
+#define any_online_cpu(mask) __any_online_cpu(&(mask))
#define for_each_cpu_mask(cpu, mask) \
for ((cpu) = first_cpu(mask); \
(cpu) < NR_CPUS; \
(cpu) = next_cpu((cpu), (mask)))
-#else /* NR_CPUS == 1 */
-#define for_each_cpu_mask(cpu, mask) \
- for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)
-#endif /* NR_CPUS */
+#endif
+
+#if NR_CPUS <= 64
+
+#define next_cpu_nr(n, src) next_cpu(n, src)
+#define cpus_weight_nr(cpumask) cpus_weight(cpumask)
+#define for_each_cpu_mask_nr(cpu, mask) for_each_cpu_mask(cpu, mask)
+
+#else /* NR_CPUS > 64 */
+
+int __next_cpu_nr(int n, const cpumask_t *srcp);
+#define next_cpu_nr(n, src) __next_cpu_nr((n), &(src))
+#define cpus_weight_nr(cpumask) __cpus_weight(&(cpumask), nr_cpu_ids)
+#define for_each_cpu_mask_nr(cpu, mask) \
+ for ((cpu) = first_cpu(mask); \
+ (cpu) < nr_cpu_ids; \
+ (cpu) = next_cpu_nr((cpu), (mask)))
+
+#endif /* NR_CPUS > 64 */
/*
* The following particular system cpumasks and operations manage
@@ -402,9 +443,9 @@ extern cpumask_t cpu_present_map;
extern cpumask_t cpu_system_map;
#if NR_CPUS > 1
-#define num_online_cpus() cpus_weight(cpu_online_map)
-#define num_possible_cpus() cpus_weight(cpu_possible_map)
-#define num_present_cpus() cpus_weight(cpu_present_map)
+#define num_online_cpus() cpus_weight_nr(cpu_online_map)
+#define num_possible_cpus() cpus_weight_nr(cpu_possible_map)
+#define num_present_cpus() cpus_weight_nr(cpu_present_map)
#define cpu_online(cpu) cpu_isset((cpu), cpu_online_map)
#define cpu_possible(cpu) cpu_isset((cpu), cpu_possible_map)
#define cpu_present(cpu) cpu_isset((cpu), cpu_present_map)
@@ -423,17 +464,8 @@ extern int cpus_match_system(cpumask_t m
#define cpu_is_offline(cpu) unlikely(!cpu_online(cpu))
-#ifdef CONFIG_SMP
-extern int nr_cpu_ids;
-#define any_online_cpu(mask) __any_online_cpu(&(mask))
-int __any_online_cpu(const cpumask_t *mask);
-#else
-#define nr_cpu_ids 1
-#define any_online_cpu(mask) 0
-#endif
-
-#define for_each_possible_cpu(cpu) for_each_cpu_mask((cpu), cpu_possible_map)
-#define for_each_online_cpu(cpu) for_each_cpu_mask((cpu), cpu_online_map)
-#define for_each_present_cpu(cpu) for_each_cpu_mask((cpu), cpu_present_map)
+#define for_each_possible_cpu(cpu) for_each_cpu_mask_nr((cpu), cpu_possible_map)
+#define for_each_online_cpu(cpu) for_each_cpu_mask_nr((cpu), cpu_online_map)
+#define for_each_present_cpu(cpu) for_each_cpu_mask_nr((cpu), cpu_present_map)
#endif /* __LINUX_CPUMASK_H */
--- linux-2.6.sched.orig/lib/cpumask.c
+++ linux-2.6.sched/lib/cpumask.c
@@ -15,6 +15,15 @@ int __next_cpu(int n, const cpumask_t *s
}
EXPORT_SYMBOL(__next_cpu);
+#if NR_CPUS > 64
+int __next_cpu_nr(int n, const cpumask_t *srcp)
+{
+ return min_t(int, nr_cpu_ids,
+ find_next_bit(srcp->bits, nr_cpu_ids, n+1));
+}
+EXPORT_SYMBOL(__next_cpu_nr);
+#endif
+
int __any_online_cpu(const cpumask_t *mask)
{
int cpu;
--
--
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