diff options
| author | Yury Norov <yury.norov@gmail.com> | 2022-09-05 16:08:19 -0700 |
|---|---|---|
| committer | Yury Norov <yury.norov@gmail.com> | 2022-09-19 17:51:53 -0700 |
| commit | aa47a7c215e79a2ade6916f163c5a17b561bce4f (patch) | |
| tree | 08452dbd0624a5e05e17e50bc76da782251fd469 /include/linux/cpumask.h | |
| parent | 7102b3bb070fdf4580a05cbfc5ad3c0691dc4bf9 (diff) | |
lib/cpumask: deprecate nr_cpumask_bits
Cpumask code is written in assumption that when CONFIG_CPUMASK_OFFSTACK
is enabled, all cpumasks have boot-time defined size, otherwise the size
is always NR_CPUS.
The latter is wrong because the number of possible cpus is always
calculated on boot, and it may be less than NR_CPUS.
On my 4-cpu arm64 VM the nr_cpu_ids is 4, as expected, and nr_cpumask_bits
is 256, which corresponds to NR_CPUS. This not only leads to useless
traversing of cpumask bits greater than 4, this also makes some cpumask
routines fail.
For example, cpumask_full(0b1111000..000) would erroneously return false
in the example above because tail bits in the mask are all unset.
This patch deprecates nr_cpumask_bits and wires it to nr_cpu_ids
unconditionally, so that cpumask routines will not waste time traversing
unused part of cpu masks. It also fixes cpumask_full() and similar
routines.
As a side effect, because now a length of cpumasks is defined at run-time
even if CPUMASK_OFFSTACK is disabled, compiler can't optimize corresponding
functions.
It increases kernel size by ~2.5KB if OFFSTACK is off. This is addressed in
the following patch.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Diffstat (limited to 'include/linux/cpumask.h')
| -rw-r--r-- | include/linux/cpumask.h | 7 |
1 files changed, 1 insertions, 6 deletions
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index 9d2f0e3e927e..2f6622cead1f 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -46,13 +46,8 @@ static inline void set_nr_cpu_ids(unsigned int nr) } #endif -#ifdef CONFIG_CPUMASK_OFFSTACK -/* Assuming NR_CPUS is huge, a runtime limit is more efficient. Also, - * not all bits may be allocated. */ +/* Deprecated. Always use nr_cpu_ids. */ #define nr_cpumask_bits nr_cpu_ids -#else -#define nr_cpumask_bits ((unsigned int)NR_CPUS) -#endif /* * The following particular system cpumasks and operations manage |