The patch titled
Subject: lib/group_cpus: optimize outer loop in grp_spread_init_one()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
lib-group_cpus-optimize-outer-loop-in-grp_spread_init_one.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-group_cpus-optimize-outer-loop-in-grp_spread_init_one.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yury Norov <yury.norov@xxxxxxxxx>
Subject: lib/group_cpus: optimize outer loop in grp_spread_init_one()
Date: Thu, 28 Dec 2023 12:09:31 -0800
Similarly to the inner loop, in the outer loop we can use for_each_cpu()
macro, and skip CPUs that have been copied.
With this patch, the function becomes O(1), despite that it's a
double-loop.
While here, add a comment why we can't merge the inner and outer logic.
Link: https://lkml.kernel.org/r/20231228200936.2475595-5-yury.norov@xxxxxxxxx
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/group_cpus.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
--- a/lib/group_cpus.c~lib-group_cpus-optimize-outer-loop-in-grp_spread_init_one
+++ a/lib/group_cpus.c
@@ -17,16 +17,17 @@ static void grp_spread_init_one(struct c
const struct cpumask *siblmsk;
int cpu, sibl;
- for ( ; cpus_per_grp > 0; ) {
- cpu = cpumask_first(nmsk);
-
- /* Should not happen, but I'm too lazy to think about it */
- if (cpu >= nr_cpu_ids)
+ for_each_cpu(cpu, nmsk) {
+ if (cpus_per_grp-- == 0)
return;
+ /*
+ * If a caller wants to spread IRQa on offline CPUs, we need to
+ * take care of it explicitly because those offline CPUS are not
+ * included in siblings cpumask.
+ */
__cpumask_clear_cpu(cpu, nmsk);
__cpumask_set_cpu(cpu, irqmsk);
- cpus_per_grp--;
/* If the cpu has siblings, use them first */
siblmsk = topology_sibling_cpumask(cpu);
@@ -38,6 +39,7 @@ static void grp_spread_init_one(struct c
__cpumask_clear_cpu(sibl, nmsk);
__cpumask_set_cpu(sibl, irqmsk);
+ cpu = sibl + 1;
}
}
}
_
Patches currently in -mm which might be from yury.norov@xxxxxxxxx are
cpumask-introduce-for_each_cpu_and_from.patch
lib-group_cpus-optimize-inner-loop-in-grp_spread_init_one.patch
lib-group_cpus-relax-atomicity-requirement-in-grp_spread_init_one.patch
lib-group_cpus-optimize-outer-loop-in-grp_spread_init_one.patch
lib-group_cpus-dont-zero-cpumasks-in-group_cpus_evenly-on-allocation.patch
lib-group_cpus-drop-unneeded-cpumask_empty-call-in-__group_cpus_evenly.patch
cpumask-define-cleanup-function-for-cpumasks.patch
lib-group_cpus-rework-group_cpus_evenly.patch
lib-group_cpus-simplify-group_cpus_evenly-for-more.patch
