diff mbox series

[v2,1/1] wq: Avoid using isolated cpus' timers on queue_delayed_work

Message ID 20240130010046.2730139-2-leobras@redhat.com
State New
Headers
Series [v2,1/1] wq: Avoid using isolated cpus' timers on queue_delayed_work |

Commit Message

Leonardo Bras Soares Passos Jan. 30, 2024, 1 a.m. UTC 
  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>
---
Changes since v1:
- Make sure the CPU is isolated for any value of "cpu"

Changes since RFC:
- Do not use the same cpu from the timer for queueing the work.
- If the current cpu is not isolated, use it's timer instead of
  looking for another candidate.

 kernel/workqueue.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

Comments

Tejun Heo Jan. 30, 2024, 1:22 a.m. UTC | #1 
On Mon, Jan 29, 2024 at 10:00:46PM -0300, Leonardo Bras wrote:
> 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>

Applied to wq/for-6.9.

Thanks.
Leonardo Bras Soares Passos Jan. 30, 2024, 2:58 a.m. UTC | #2 
On Mon, Jan 29, 2024 at 03:22:33PM -1000, Tejun Heo wrote:
> On Mon, Jan 29, 2024 at 10:00:46PM -0300, Leonardo Bras wrote:
> > 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>
> 
> Applied to wq/for-6.9.
> 
> Thanks.
> 
> -- 
> tejun
> 

Thank you!
Leo
diff mbox series

Patch

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 76e60faed8923..8dd7c01b326a4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1958,10 +1958,18 @@  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);
+	}
 }
 
 /**