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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-08-10 14:33:17 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-10-09 14:23:36 -0700
commit3d916a443e97169a3d88765c4e0b07ac813f439f (patch)
tree2014eaee2f3b3a8a2fcd1311413cbf48c1e44f3c /Documentation/RCU
parentdfa0ee48ef86f79430d2be9d1e2e1b509abb3cce (diff)
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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: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/stallwarn.txt6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 21b8913acbdf..238acbd94917 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -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
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