diff options
| author | Yury Norov [NVIDIA] <yury.norov@gmail.com> | 2025-06-19 14:26:25 -0400 |
|---|---|---|
| committer | Yury Norov <yury.norov@gmail.com> | 2025-07-31 11:27:48 -0400 |
| commit | 8557c8628cf3cf8ebd3b32601ccdde550bbf6c54 (patch) | |
| tree | d93dcf9819b8999760aec589411511e82a5732cf /kernel | |
| parent | 012b1043420c0bc62e52902499de40b66f37fd6a (diff) | |
clocksource: Improve randomness in clocksource_verify_choose_cpus()
The current algorithm of picking a random CPU works OK for dense online
cpumask, but if cpumask is non-dense, the distribution of picked CPUs
is skewed.
For example, on 8-CPU board with CPUs 4-7 offlined, the probability of
selecting CPU 0 is 5/8. Accordingly, cpus 1, 2 and 3 are chosen with
probability 1/8 each. The proper algorithm should pick each online CPU
with probability 1/4.
Switch it to cpumask_random(), which has better statistical
characteristics.
CC: Andrew Morton <akpm@linux-foundation.org>
Acked-by: John Stultz <jstultz@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Yury Norov [NVIDIA]" <yury.norov@gmail.com>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/time/clocksource.c | 5 |
1 files changed, 1 insertions, 4 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 6a8bc7da9062..4b005b2f3ef5 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -342,10 +342,7 @@ static void clocksource_verify_choose_cpus(void) * CPUs that are currently online. */ for (i = 1; i < n; i++) { - cpu = get_random_u32_below(nr_cpu_ids); - cpu = cpumask_next(cpu - 1, cpu_online_mask); - if (cpu >= nr_cpu_ids) - cpu = cpumask_first(cpu_online_mask); + cpu = cpumask_random(cpu_online_mask); if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) cpumask_set_cpu(cpu, &cpus_chosen); } |