linux-kernel - [tip: core/rseq] sched/mmcid: Use cpumask_weighted

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Message-ID: <176363760125.498.15227477726391042766.tip-bot2@tip-bot2>
Date: Thu, 20 Nov 2025 11:20:01 -0000
From: "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 "Yury Norov (NVIDIA)" <yury.norov@...il.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: core/rseq] sched/mmcid: Use cpumask_weighted_or()

The following commit has been merged into the core/rseq branch of tip:

Commit-ID:     79c11fb3da8581a2f222b290ce62a153ab1108fc
Gitweb:        https://git.kernel.org/tip/79c11fb3da8581a2f222b290ce62a153ab1108fc
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 19 Nov 2025 18:26:59 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 20 Nov 2025 12:14:54 +01:00

sched/mmcid: Use cpumask_weighted_or()

Use cpumask_weighted_or() instead of cpumask_or() and cpumask_weight() on
the result, which walks the same bitmap twice. Results in 10-20% less
cycles, which reduces the runqueue lock hold time.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Acked-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
Link: https://patch.msgid.link/20251119172549.511736272@linutronix.de
---
 kernel/sched/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2ea77e7..f6bbfa1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10377,6 +10377,7 @@ void call_trace_sched_update_nr_running(struct rq *rq, int count)
 static inline void mm_update_cpus_allowed(struct mm_struct *mm, const struct cpumask *affmsk)
 {
 	struct cpumask *mm_allowed;
+	unsigned int weight;
 
 	if (!mm)
 		return;
@@ -10387,8 +10388,8 @@ static inline void mm_update_cpus_allowed(struct mm_struct *mm, const struct cpu
 	 */
 	guard(raw_spinlock)(&mm->mm_cid.lock);
 	mm_allowed = mm_cpus_allowed(mm);
-	cpumask_or(mm_allowed, mm_allowed, affmsk);
-	WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, cpumask_weight(mm_allowed));
+	weight = cpumask_weighted_or(mm_allowed, mm_allowed, affmsk);
+	WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, weight);
 }
 
 void sched_mm_cid_exit_signals(struct task_struct *t)