workqueue: Avoid using isolated cpus' timers on queue_delayed_work

When __queue_delayed_work() is called, it chooses a cpu for handling the
timer interrupt. As of today, it will pick either the cpu passed as
parameter or the last cpu used for this.

This is not good if a system does use CPU isolation, because it can take
away some valuable cpu time to:
1 - deal with the timer interrupt,
2 - schedule-out the desired task,
3 - queue work on a random workqueue, and
4 - schedule the desired task back to the cpu.

So to fix this, during __queue_delayed_work(), if cpu isolation is in
place, pick a random non-isolated cpu to handle the timer interrupt.

As an optimization, if the current cpu is not isolated, use it instead
of looking for another candidate.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 903be39bd2d19bfd12c509db5231a3a198f4c79c..9221a4c57ae1c5c23cfec552bcdcf9abdf8fd6ac 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2362,10 +2362,18 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
        dwork->cpu = cpu;
        timer->expires = jiffies + delay;
 
-       if (unlikely(cpu != WORK_CPU_UNBOUND))
+       if (housekeeping_enabled(HK_TYPE_TIMER)) {
+               /* If the current cpu is a housekeeping cpu, use it. */
+               cpu = smp_processor_id();
+               if (!housekeeping_test_cpu(cpu, HK_TYPE_TIMER))
+                       cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
                add_timer_on(timer, cpu);
-       else
-               add_timer(timer);
+       } else {
+               if (likely(cpu == WORK_CPU_UNBOUND))
+                       add_timer(timer);
+               else
+                       add_timer_on(timer, cpu);
+       }
 }
 
 /**