diff mbox series

rcu: Use system_unbound_wq to avoid disturbing isolated CPUs

Message ID 20240816071109.63059-1-neeraj.upadhyay@kernel.org (mailing list archive)
State New, archived
Headers show
Series rcu: Use system_unbound_wq to avoid disturbing isolated CPUs | expand

Commit Message

Neeraj Upadhyay Aug. 16, 2024, 7:11 a.m. UTC 
From: Waiman Long <longman@redhat.com>

It was discovered that isolated CPUs could sometimes be disturbed by
kworkers processing kfree_rcu() works causing higher than expected
latency. It is because the RCU core uses "system_wq" which doesn't have
the WQ_UNBOUND flag to handle all its work items. Fix this violation of
latency limits by using "system_unbound_wq" in the RCU core instead.
This will ensure that those work items will not be run on CPUs marked
as isolated.

Beside the WQ_UNBOUND flag, the other major difference between system_wq
and system_unbound_wq is their max_active count. The system_unbound_wq
has a max_active of WQ_MAX_ACTIVE (512) while system_wq's max_active
is WQ_DFL_ACTIVE (256) which is half of WQ_MAX_ACTIVE.

Reported-by: Vratislav Bendel <vbendel@redhat.com>
Closes: https://issues.redhat.com/browse/RHEL-50220
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Tested-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
---
 kernel/rcu/tree.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e641cc681901..494aa9513d0b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3539,10 +3539,10 @@  schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
 	if (delayed_work_pending(&krcp->monitor_work)) {
 		delay_left = krcp->monitor_work.timer.expires - jiffies;
 		if (delay < delay_left)
-			mod_delayed_work(system_wq, &krcp->monitor_work, delay);
+			mod_delayed_work(system_unbound_wq, &krcp->monitor_work, delay);
 		return;
 	}
-	queue_delayed_work(system_wq, &krcp->monitor_work, delay);
+	queue_delayed_work(system_unbound_wq, &krcp->monitor_work, delay);
 }
 
 static void
@@ -3634,7 +3634,7 @@  static void kfree_rcu_monitor(struct work_struct *work)
 			// be that the work is in the pending state when
 			// channels have been detached following by each
 			// other.
-			queue_rcu_work(system_wq, &krwp->rcu_work);
+			queue_rcu_work(system_unbound_wq, &krwp->rcu_work);
 		}
 	}
 
@@ -3704,7 +3704,7 @@  run_page_cache_worker(struct kfree_rcu_cpu *krcp)
 	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
 			!atomic_xchg(&krcp->work_in_progress, 1)) {
 		if (atomic_read(&krcp->backoff_page_cache_fill)) {
-			queue_delayed_work(system_wq,
+			queue_delayed_work(system_unbound_wq,
 				&krcp->page_cache_work,
 					msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
 		} else {