workqueue: Avoid using isolated cpus' timers on queue_delayed_work

JIRA: https://issues.redhat.com/browse/RHEL-20254
Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git/

commit aae17eb
Author: Leonardo Bras <leobras@redhat.com>
Date:   Mon Jan 29 22:00:46 2024 -0300

    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>

Signed-off-by: Leonardo Bras <leobras@redhat.com>

Author: Leonardo Bras

kernel/workqueue.c

@@ -1677,10 +1677,18 @@ 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);
+	}
 }
 
 /**