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Commit ef557180 authored by Mike Galbraith's avatar Mike Galbraith Committed by Tejun Heo
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workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs 



WORK_CPU_UNBOUND work items queued to a bound workqueue always run
locally.  This is a good thing normally, but not when the user has
asked us to keep unbound work away from certain CPUs.  Round robin
these to wq_unbound_cpumask CPUs instead, as perturbation avoidance
trumps performance.

tj: Cosmetic and comment changes.  WARN_ON_ONCE() dropped from empty
    (wq_unbound_cpumask AND cpu_online_mask).  If we want that, it
    should be done when config changes.

Signed-off-by: default avatarMike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 041bd12e

kernel/workqueue.c

+32 −2
Original line number Diff line number Diff line
@@ -301,7 +301,11 @@ static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */ 
static LIST_HEAD(workqueues);		/* PR: list of all workqueues */

static bool workqueue_freezing;		/* PL: have wqs started freezing? */



static cpumask_var_t wq_unbound_cpumask; /* PL: low level cpumask for all unbound wqs */

/* PL: allowable cpus for unbound wqs and work items */

static cpumask_var_t wq_unbound_cpumask;



/* CPU where unbound work was last round robin scheduled from this CPU */

static DEFINE_PER_CPU(int, wq_rr_cpu_last);



/* the per-cpu worker pools */

static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
@@ -1298,6 +1302,32 @@ static bool is_chained_work(struct workqueue_struct *wq) 
	return worker && worker->current_pwq->wq == wq;

}



/*

 * When queueing an unbound work item to a wq, prefer local CPU if allowed

 * by wq_unbound_cpumask.  Otherwise, round robin among the allowed ones to

 * avoid perturbing sensitive tasks.

 */

static int wq_select_unbound_cpu(int cpu)

{

	int new_cpu;



	if (cpumask_test_cpu(cpu, wq_unbound_cpumask))

		return cpu;

	if (cpumask_empty(wq_unbound_cpumask))

		return cpu;



	new_cpu = __this_cpu_read(wq_rr_cpu_last);

	new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);

	if (unlikely(new_cpu >= nr_cpu_ids)) {

		new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);

		if (unlikely(new_cpu >= nr_cpu_ids))

			return cpu;

	}

	__this_cpu_write(wq_rr_cpu_last, new_cpu);



	return new_cpu;

}



static void __queue_work(int cpu, struct workqueue_struct *wq,

			 struct work_struct *work)

{
@@ -1323,7 +1353,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
		return;

retry:

	if (req_cpu == WORK_CPU_UNBOUND)

		cpu = raw_smp_processor_id();

		cpu = wq_select_unbound_cpu(raw_smp_processor_id());



	/* pwq which will be used unless @work is executing elsewhere */

	if (!(wq->flags & WQ_UNBOUND))