linux-kernel - [PATCH] mark power efficient workqueue as unbounded if nohz

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Date: Fri, 19 Jan 2024 12:54:39 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Joe Mario <jmario@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] mark power efficient workqueue as unbounded if nohz_full
 enabled


A customer using nohz_full has experienced the following interruption:

oslat-1004510 [018] timer_cancel:         timer=0xffff90a7ca663cf8
oslat-1004510 [018] timer_expire_entry:   timer=0xffff90a7ca663cf8 function=delayed_work_timer_fn now=4709188240 baseclk=4709188240
oslat-1004510 [018] workqueue_queue_work: work struct=0xffff90a7ca663cd8 function=fb_flashcursor workqueue=events_power_efficient req_cpu=8192 cpu=18
oslat-1004510 [018] workqueue_activate_work: work struct 0xffff90a7ca663cd8
oslat-1004510 [018] sched_wakeup:         kworker/18:1:326 [120] CPU:018
oslat-1004510 [018] timer_expire_exit:    timer=0xffff90a7ca663cf8
oslat-1004510 [018] irq_work_entry:       vector=246
oslat-1004510 [018] irq_work_exit:        vector=246
oslat-1004510 [018] tick_stop:            success=0 dependency=SCHED
oslat-1004510 [018] hrtimer_start:        hrtimer=0xffff90a70009cb00 function=tick_sched_timer/0x0 ...
oslat-1004510 [018] softirq_exit:         vec=1 [action=TIMER]
oslat-1004510 [018] softirq_entry:        vec=7 [action=SCHED]
oslat-1004510 [018] softirq_exit:         vec=7 [action=SCHED]
oslat-1004510 [018] tick_stop:            success=0 dependency=SCHED
oslat-1004510 [018] sched_switch:         oslat:1004510 [120] R ==> kworker/18:1:326 [120]
kworker/18:1-326 [018] workqueue_execute_start: work struct 0xffff90a7ca663cd8: function fb_flashcursor
kworker/18:1-326 [018] workqueue_queue_work: work struct=0xffff9078f119eed0 function=drm_fb_helper_damage_work workqueue=events req_cpu=8192 cpu=18
kworker/18:1-326 [018] workqueue_activate_work: work struct 0xffff9078f119eed0
kworker/18:1-326 [018] timer_start:          timer=0xffff90a7ca663cf8 function=delayed_work_timer_fn ...

Set wq_power_efficient to true, in case nohz_full is enabled. 
This makes the power efficient workqueue be unbounded, which allows
workqueue items there to be moved to HK CPUs.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>


diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 76e60faed892..45b3a63954a9 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -6630,6 +6630,13 @@ void __init workqueue_init_early(void)
 	wq_update_pod_attrs_buf = alloc_workqueue_attrs();
 	BUG_ON(!wq_update_pod_attrs_buf);
 
+	/*
+	 * If nohz_full is enabled, set power efficient workqueue as unbound.
+	 * This allows workqueue items to be moved to HK CPUs.
+	 */
+	if (housekeeping_enabled(HK_TYPE_TICK))
+		wq_power_efficient = true;
+
 	/* initialize WQ_AFFN_SYSTEM pods */
 	pt->pod_cpus = kcalloc(1, sizeof(pt->pod_cpus[0]), GFP_KERNEL);
 	pt->pod_node = kcalloc(1, sizeof(pt->pod_node[0]), GFP_KERNEL);