The runqueue clock is supposed to be periodically updated by the tick. On full dynticks CPU we call update_nohz_rq_clock() before reading it. Now the scheduler code is complicated enough that we may miss some update_nohz_rq_clock() calls before reading the runqueue clock.
This therefore introduce a new debugging feature that detects when the rq clock is stale due to missing updates on full dynticks CPUs. This can be later expanded to debug stale clocks on dynticks-idle CPUs. Signed-off-by: Frederic Weisbecker <[email protected]> Cc: Alessio Igor Bogani <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Geoff Levand <[email protected]> Cc: Gilad Ben Yossef <[email protected]> Cc: Hakan Akkan <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Li Zhong <[email protected]> Cc: Namhyung Kim <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Paul Gortmaker <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Thomas Gleixner <[email protected]> --- kernel/sched/sched.h | 23 +++++++++++++++++++++++ 1 files changed, 23 insertions(+), 0 deletions(-) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e1bac76..0fef0b3 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -502,16 +502,39 @@ DECLARE_PER_CPU(struct rq, runqueues); #define cpu_curr(cpu) (cpu_rq(cpu)->curr) #define raw_rq() (&__raw_get_cpu_var(runqueues)) +static inline void rq_clock_check(struct rq *rq) +{ +#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_NO_HZ_FULL) + unsigned long long clock; + unsigned long flags; + int cpu; + + cpu = cpu_of(rq); + if (!tick_nohz_full_cpu(cpu) || rq->curr == rq->idle) + return; + + local_irq_save(flags); + clock = sched_clock_cpu(cpu_of(rq)); + local_irq_restore(flags); + + if (abs(clock - rq->clock) > (TICK_NSEC * 3)) + WARN_ON_ONCE(1); +#endif +} + static inline u64 rq_clock(struct rq *rq) { + rq_clock_check(rq); return rq->clock; } static inline u64 rq_clock_task(struct rq *rq) { + rq_clock_check(rq); return rq->clock_task; } + #ifdef CONFIG_SMP #define rcu_dereference_check_sched_domain(p) \ -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
