From 83dc4617b90353aea672cd365c99e6cad6df5e85 Mon Sep 17 00:00:00 2001 From: Cheng Jian Date: Wed, 9 Jun 2021 13:53:39 +0800 Subject: [PATCH 2920/2944] sched/fair: Optimize select_idle_cpu fix #34890870 commit 60588bfa223ff675b95f866249f90616613fbe31 upstream. select_idle_cpu() will scan the LLC domain for idle CPUs, it's always expensive. so the next commit : 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") introduces a way to limit how many CPUs we scan. But it consume some CPUs out of 'nr' that are not allowed for the task and thus waste our attempts. The function always return nr_cpumask_bits, and we can't find a CPU which our task is allowed to run. Cpumask may be too big, similar to select_idle_core(), use per_cpu_ptr 'select_idle_mask' to prevent stack overflow. Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") Signed-off-by: Cheng Jian Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Srikar Dronamraju Reviewed-by: Vincent Guittot Reviewed-by: Valentin Schneider Link: https://lkml.kernel.org/r/20191213024530.28052-1-cj.chengjian@huawei.com Signed-off-by: Yang Wei Acked-by: Michael Wang --- kernel/sched/fair.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 5f66a7f..ad2aaa3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7366,6 +7366,7 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd */ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target) { + struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); struct sched_domain *this_sd; u64 avg_cost, avg_idle; u64 time, cost; @@ -7399,13 +7400,14 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t time = local_clock(); is_expellee = is_expellee_task(p); - for_each_cpu_wrap(cpu, sched_domain_span(sd), target) { + + cpumask_and(cpus, sched_domain_span(sd), &p->cpus_allowed); + + for_each_cpu_wrap(cpu, cpus, target) { bool idle; if (!--nr) return -1; - if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) - continue; /* * Here is the best opportunity to locate a real -- 1.8.3.1