* 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>
The nr_cpu_ids value is currently only calculated in smp_init. However, it
may be needed before (SLUB needs it on kmem_cache_init!) and other kernel
components may also want to allocate dynamically sized per cpu array before
smp_init. So move the determination of possible cpus into sched_init()
where we already loop over all possible cpus early in boot.
Also initialize both nr_node_ids and nr_cpu_ids with the highest value they
could take. If we have accidental users before these values are determined
then the current valud of 0 may cause too small per cpu and per node arrays
to be allocated. If it is set to the maximum possible then we only waste
some memory for early boot users.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We frequently need the maximum number of possible processors in order to
allocate arrays for all processors. So far this was done using
highest_possible_processor_id(). However, we do need the number of
processors not the highest id. Moreover the number was so far dynamically
calculated on each invokation. The number of possible processors does not
change when the system is running. We can therefore calculate that number
once.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Frederik Deweerdt <frederik.deweerdt@gmail.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Qooting Adrian:
- net/sunrpc/svc.c uses highest_possible_node_id()
- include/linux/nodemask.h says highest_possible_node_id() is
out-of-line #if MAX_NUMNODES > 1
- the out-of-line highest_possible_node_id() is in lib/cpumask.c
- lib/Makefile: lib-$(CONFIG_SMP) += cpumask.o
CONFIG_ARCH_DISCONTIGMEM_ENABLE=y, CONFIG_SMP=n, CONFIG_SUNRPC=y
-> highest_possible_node_id() is used in net/sunrpc/svc.c
CONFIG_NODES_SHIFT defined and > 0
-> include/linux/numa.h: MAX_NUMNODES > 1
-> compile error
The bug is not present on architectures where ARCH_DISCONTIGMEM_ENABLE
depends on NUMA (but m32r isn't the only affected architecture).
So move the function into page_alloc.c
Cc: Adrian Bunk <bunk@stusta.de>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
text data bss dec hex filename
before: 3605597 1363528 363328 5332453 515de5 vmlinux
after: 3605295 1363612 363200 5332107 515c8b vmlinux
218 bytes saved.
Also, optimise any_online_cpu() out of existence on CONFIG_SMP=n.
This function seems inefficient. Can't we simply AND the two masks, then use
find_first_bit()?
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Shrinks the only caller (net/bridge/netfilter/ebtables.c) by 174 bytes.
Also, optimise highest_possible_processor_id() out of existence on
CONFIG_SMP=n.
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
