sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance (5fb52dd9) · Commits · 戴 / test

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 <mgorman@techsingularity.net> Signed-off-by:

Ingo Molnar <mingo@kernel.org> Acked-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Phil Auld <pauld@redhat.com> Cc: Hillf Danton <hdanton@sina.com> Link: https://lore.kernel.org/r/20200224095223.13361-12-mgorman@techsingularity.net

kernel/sched/fair.c

+22 −18

Original line number	Diff line number	Diff line
		@@ -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;
		}

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