From ba190ed3f47f0e177e4be525d4a6330bd2fbd1f1 Mon Sep 17 00:00:00 2001 From: Andrea Righi Date: Mon, 3 Aug 2026 08:08:12 +0200 Subject: [PATCH] sched_ext: Initialize idle masks as busy The built-in idle masks are reset with all online CPUs marked idle before sched_ext is enabled. Busy CPUs can therefore be incorrectly advertised as idle until their next idle transition. Initialize the masks empty so that the initial state is conservative. When bypass is lifted, every CPU is rescheduled and idle-to-idle re-picks populate the masks with CPUs that are actually idle. Later idle transitions keep the masks up to date. Suggested-by: Tejun Heo Signed-off-by: Andrea Righi Reviewed-by: Kuba Piecuch Signed-off-by: Tejun Heo --- kernel/sched/ext/idle.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/kernel/sched/ext/idle.c b/kernel/sched/ext/idle.c index 3e9d6a44bf43..33bd51ab3ced 100644 --- a/kernel/sched/ext/idle.c +++ b/kernel/sched/ext/idle.c @@ -838,20 +838,20 @@ static void reset_idle_masks(struct sched_ext_ops *ops) int node; /* - * Consider all online cpus idle. Should converge to the actual state - * quickly. + * Start with all CPUs marked busy. The idle masks are populated when + * bypass is lifted and each idle CPU is forced through an idle re-pick. + * This may temporarily omit idle CPUs but never advertises a busy CPU as + * idle. */ if (!(ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)) { - cpumask_copy(idle_cpumask(NUMA_NO_NODE)->cpu, cpu_online_mask); - cpumask_copy(idle_cpumask(NUMA_NO_NODE)->smt, cpu_online_mask); + cpumask_clear(idle_cpumask(NUMA_NO_NODE)->cpu); + cpumask_clear(idle_cpumask(NUMA_NO_NODE)->smt); return; } for_each_node(node) { - const struct cpumask *node_mask = cpumask_of_node(node); - - cpumask_and(idle_cpumask(node)->cpu, cpu_online_mask, node_mask); - cpumask_and(idle_cpumask(node)->smt, cpu_online_mask, node_mask); + cpumask_clear(idle_cpumask(node)->cpu); + cpumask_clear(idle_cpumask(node)->smt); } }