Commit 3d916a44 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

documentation: Slow systems can stall RCU grace periods 



If a fast system has a worst-case grace-period duration of (say) ten
seconds, then running the same workload on a system ten times as slow
will get you an RCU CPU stall warning given default stall-warning
timeout settings.  This commit therefore adds this possibility to
stallwarn.txt.

Reported-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent dfa0ee48

Documentation/RCU/stallwarn.txt

+6 −0
Original line number Original line Diff line number Diff line
@@ -70,6 +70,12 @@ o A periodic interrupt whose handler takes longer than the time 
	considerably longer than normal, which can in turn result in

	considerably longer than normal, which can in turn result in

	RCU CPU stall warnings.

	RCU CPU stall warnings.





o	Testing a workload on a fast system, tuning the stall-warning

	timeout down to just barely avoid RCU CPU stall warnings, and then

	running the same workload with the same stall-warning timeout on a

	slow system.  Note that thermal throttling and on-demand governors

	can cause a single system to be sometimes fast and sometimes slow!



o	A hardware or software issue shuts off the scheduler-clock

o	A hardware or software issue shuts off the scheduler-clock

	interrupt on a CPU that is not in dyntick-idle mode.  This

	interrupt on a CPU that is not in dyntick-idle mode.  This

	problem really has happened, and seems to be most likely to

	problem really has happened, and seems to be most likely to