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documentation: Slow systems can stall RCU grace periods

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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: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-08-10 14:33:17 -07:00
parent dfa0ee48ef
commit 3d916a443e
1 changed files with 6 additions and 0 deletions
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6
Documentation/RCU/stallwarn.txt
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@ -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
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
interrupt on a CPU that is not in dyntick-idle mode. This
problem really has happened, and seems to be most likely to