[PATCH 4/4] x86/resctrl: optimize cpumask_any_housekeeping()

Yury Norov
2025-04-07T15:39:04Z

From: Yury Norov [NVIDIA] <yury.norov@gmail.com>

With the lack of cpumask_andnot_any_but(), users have to abuse
cpumask_nth() functions which are O(N*log(N)), comparing to O(N)
for cpumask_any().

This series adds missing cpumask_andnot_any_but() and makes
cpumask_any_but() understanding the RESCTRL_PICK_ANY_CPU hint.
This simplifies cpumask_any_housekeeping() significantly.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
---
arch/x86/kernel/cpu/resctrl/internal.h | 28 +++++++-------------------
1 file changed, 7 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 20c898f09b7e..1db02bab9743 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -71,30 +71,16 @@
static inline unsigned int
cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
{
- unsigned int cpu, hk_cpu;
-
- if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
- cpu = cpumask_any(mask);
- else
- cpu = cpumask_any_but(mask, exclude_cpu);
-
- /* Only continue if tick_nohz_full_mask has been initialized. */
- if (!tick_nohz_full_enabled())
- return cpu;
-
- /* If the CPU picked isn't marked nohz_full nothing more needs doing. */
- if (cpu < nr_cpu_ids && !tick_nohz_full_cpu(cpu))
- return cpu;
+ unsigned int cpu;

/* Try to find a CPU that isn't nohz_full to use in preference */
- hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
- if (hk_cpu == exclude_cpu)
- hk_cpu = cpumask_nth_andnot(1, mask, tick_nohz_full_mask);
-
- if (hk_cpu < nr_cpu_ids)
- cpu = hk_cpu;
+ if (tick_nohz_full_enabled()) {
+ cpu = cpumask_andnot_any_but(mask, tick_nohz_full_mask, exclude_cpu);
+ if (cpu < nr_cpu_ids)
+ return cpu;
+ }

- return cpu;
+ return cpumask_any_but(mask, exclude_cpu);
}

struct rdt_fs_context {
--
2.43.0