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author | Mike Travis <travis@sgi.com> | 2008-05-12 21:21:13 +0200 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2008-05-23 18:23:38 +0200 |
commit | 41df0d61c266998b8049df7fec119cd518a43aa1 (patch) | |
tree | 6791fa6e3fdaee51ae348f9fe63972d648beaf5a /drivers/acpi/processor_throttling.c | |
parent | 143aa5c53bd3895d42d7c08753fe58293988a69d (diff) | |
download | linux-41df0d61c266998b8049df7fec119cd518a43aa1.tar.gz linux-41df0d61c266998b8049df7fec119cd518a43aa1.tar.bz2 linux-41df0d61c266998b8049df7fec119cd518a43aa1.zip |
x86: Add performance variants of cpumask operators
* 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>
Diffstat (limited to 'drivers/acpi/processor_throttling.c')
0 files changed, 0 insertions, 0 deletions