mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-24 19:45:06 +08:00
41df0d61c2
* 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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
38 lines
752 B
C
38 lines
752 B
C
#include <linux/kernel.h>
|
|
#include <linux/bitops.h>
|
|
#include <linux/cpumask.h>
|
|
#include <linux/module.h>
|
|
|
|
int __first_cpu(const cpumask_t *srcp)
|
|
{
|
|
return min_t(int, NR_CPUS, find_first_bit(srcp->bits, NR_CPUS));
|
|
}
|
|
EXPORT_SYMBOL(__first_cpu);
|
|
|
|
int __next_cpu(int n, const cpumask_t *srcp)
|
|
{
|
|
return min_t(int, NR_CPUS, find_next_bit(srcp->bits, NR_CPUS, n+1));
|
|
}
|
|
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;
|
|
|
|
for_each_cpu_mask(cpu, *mask) {
|
|
if (cpu_online(cpu))
|
|
break;
|
|
}
|
|
return cpu;
|
|
}
|
|
EXPORT_SYMBOL(__any_online_cpu);
|