linux-kernel - [PATCH 2/3] sched/fair: Ignore isolated cpus in update_numa

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Message-Id: <20241216122357.1276382-3-zhouchuyi@bytedance.com>
Date: Mon, 16 Dec 2024 20:23:56 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com
Cc: chengming.zhou@...ux.dev,
	linux-kernel@...r.kernel.org,
	Chuyi Zhou <zhouchuyi@...edance.com>
Subject: [PATCH 2/3] sched/fair: Ignore isolated cpus in update_numa_stat

Now update_numa_stats() iterates each cpu in a node to gather load
information for the node and attempts to find the idle cpu as a candidate
best_cpu within the node.

In update_numa_stats() we should take into account the scheduling domain.
This is because the "isolcpus" kernel command line option and cpuset iso-
late partitions can remove CPUs from load balance. Similar to task wakeup
and periodic load balancing, we should not involve isolated CPUs in NUMA
balancing. When gathering load information for nodes, we need to ignore the
load of isolated CPUs. This change also avoids selecting an isolated CPU
as the idle_cpu.

Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
---
 kernel/sched/fair.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f544012b9320..a0139659fe7a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2125,6 +2125,11 @@ static void update_numa_stats(struct task_numa_env *env,
 	for_each_cpu(cpu, cpumask_of_node(nid)) {
 		struct rq *rq = cpu_rq(cpu);

+		/* skip isolated cpus' load */
+		if (!rcu_dereference(rq->sd))
+			continue;
+
+		ns->weight++;
 		ns->load += cpu_load(rq);
 		ns->runnable += cpu_runnable(rq);
 		ns->util += cpu_util_cfs(cpu);
@@ -2144,8 +2149,6 @@ static void update_numa_stats(struct task_numa_env *env,
 	}
 	rcu_read_unlock();

-	ns->weight = cpumask_weight(cpumask_of_node(nid));
-
 	ns->node_type = numa_classify(env->imbalance_pct, ns);

 	if (idle_core >= 0)
-- 
2.20.1