sched: Debug nohz rq clock
The runqueue clock progression is maintained in 3 ways:
* Periodically with the timer tick
* On an as needed basis through update_rq_clock() calls
when we want a fresh update or we want to update the rq
clock of a dynticks CPU
* On full dynticks CPUs with explicit calls to
update_nohz_rq_clock()
But it's easy to miss some rq clock updates in the middle
of the tricky scheduler code paths.
So let's add some automatic debug check for stale rq
clock values when we read these. For now this just
consists in warning when we read an rq clock that hasn't
been updated for more than 30 seconds. We need a bit of
an error margin due to wheezy rq clock updates on boot.
We can certainly do some more clever check, considering
rq->skip_clock_update for example, and perhaps the rq clock
doesn't always need a fresh update on every place so
that detection is perhaps not relevant in every case.
But we need to start somewhere.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul Turner <pjt@google.com>
Cc: Mike Galbraith <efault@gmx.de>
2 files changed
