Skip to content

Commit

Permalink
documentation: Slow systems can stall RCU grace periods
Browse files Browse the repository at this point in the history
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>
  • Loading branch information
Paul E. McKenney committed Oct 9, 2017
1 parent dfa0ee4 commit 3d916a4
Showing 1 changed file with 6 additions and 0 deletions.
6 changes: 6 additions & 0 deletions Documentation/RCU/stallwarn.txt
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down

0 comments on commit 3d916a4

Please sign in to comment.