This is a note to let you know that I've just added the patch titled
workqueue: Improve scalability of workqueue watchdog touch
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
workqueue-improve-scalability-of-workqueue-watchdog-.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit d1f93f72f0cd3e8694b3b9b6f5a2c44cefefc893
Author: Nicholas Piggin <npiggin@xxxxxxxxx>
Date: Tue Jun 25 21:42:45 2024 +1000
workqueue: Improve scalability of workqueue watchdog touch
[ Upstream commit 98f887f820c993e05a12e8aa816c80b8661d4c87 ]
On a ~2000 CPU powerpc system, hard lockups have been observed in the
workqueue code when stop_machine runs (in this case due to CPU hotplug).
This is due to lots of CPUs spinning in multi_cpu_stop, calling
touch_nmi_watchdog() which ends up calling wq_watchdog_touch().
wq_watchdog_touch() writes to the global variable wq_watchdog_touched,
and that can find itself in the same cacheline as other important
workqueue data, which slows down operations to the point of lockups.
In the case of the following abridged trace, worker_pool_idr was in
the hot line, causing the lockups to always appear at idr_find.
watchdog: CPU 1125 self-detected hard LOCKUP @ idr_find
Call Trace:
get_work_pool
__queue_work
call_timer_fn
run_timer_softirq
__do_softirq
do_softirq_own_stack
irq_exit
timer_interrupt
decrementer_common_virt
* interrupt: 900 (timer) at multi_cpu_stop
multi_cpu_stop
cpu_stopper_thread
smpboot_thread_fn
kthread
Fix this by having wq_watchdog_touch() only write to the line if the
last time a touch was recorded exceeds 1/4 of the watchdog threshold.
Reported-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a1665c2e04b4..7fa1c7c9151a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -6456,12 +6456,18 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
notrace void wq_watchdog_touch(int cpu)
{
+ unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
+ unsigned long touch_ts = READ_ONCE(wq_watchdog_touched);
+ unsigned long now = jiffies;
+
if (cpu >= 0)
- per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
+ per_cpu(wq_watchdog_touched_cpu, cpu) = now;
else
WARN_ONCE(1, "%s should be called with valid CPU", __func__);
- wq_watchdog_touched = jiffies;
+ /* Don't unnecessarily store to global cacheline */
+ if (time_after(now, touch_ts + thresh / 4))
+ WRITE_ONCE(wq_watchdog_touched, jiffies);
}
static void wq_watchdog_set_thresh(unsigned long thresh)
