From 5fb52dd93a2fe9a738f730de9da108bd1f6c30d0 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Mon, 24 Feb 2020 09:52:21 +0000 Subject: [PATCH] sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance Multiple tasks can attempt to select and idle CPU but fail because numa_migrate_on is already set and the migration fails. Instead of failing, scan for an alternative idle CPU. select_idle_sibling is not used because it requires IRQs to be disabled and it ignores numa_migrate_on allowing multiple tasks to stack. This scan may still fail if there are idle candidate CPUs due to races but if this occurs, it's best that a task stay on an available CPU that move to a contended one. Signed-off-by: Mel Gorman Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Vincent Guittot Cc: Juri Lelli Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Valentin Schneider Cc: Phil Auld Cc: Hillf Danton Link: https://lore.kernel.org/r/20200224095223.13361-12-mgorman@techsingularity.net --- kernel/sched/fair.c | 40 ++++++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 18 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2da21f4..050c1b1 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1624,15 +1624,34 @@ static void task_numa_assign(struct task_numa_env *env, { struct rq *rq = cpu_rq(env->dst_cpu); - /* Bail out if run-queue part of active NUMA balance. */ - if (env->best_cpu != env->dst_cpu && xchg(&rq->numa_migrate_on, 1)) + /* Check if run-queue part of active NUMA balance. */ + if (env->best_cpu != env->dst_cpu && xchg(&rq->numa_migrate_on, 1)) { + int cpu; + int start = env->dst_cpu; + + /* Find alternative idle CPU. */ + for_each_cpu_wrap(cpu, cpumask_of_node(env->dst_nid), start) { + if (cpu == env->best_cpu || !idle_cpu(cpu) || + !cpumask_test_cpu(cpu, env->p->cpus_ptr)) { + continue; + } + + env->dst_cpu = cpu; + rq = cpu_rq(env->dst_cpu); + if (!xchg(&rq->numa_migrate_on, 1)) + goto assign; + } + + /* Failed to find an alternative idle CPU */ return; + } +assign: /* * Clear previous best_cpu/rq numa-migrate flag, since task now * found a better CPU to move/swap. */ - if (env->best_cpu != -1) { + if (env->best_cpu != -1 && env->best_cpu != env->dst_cpu) { rq = cpu_rq(env->best_cpu); WRITE_ONCE(rq->numa_migrate_on, 0); } @@ -1806,21 +1825,6 @@ assign: cpu = env->best_cpu; } - /* - * Use select_idle_sibling if the previously found idle CPU is - * not idle any more. - */ - if (!idle_cpu(cpu)) { - /* - * select_idle_siblings() uses an per-CPU cpumask that - * can be used from IRQ context. - */ - local_irq_disable(); - cpu = select_idle_sibling(env->p, env->src_cpu, - env->dst_cpu); - local_irq_enable(); - } - env->dst_cpu = cpu; } -- 2.7.4