On Mon, Feb 26, 2018 at 09:29:20PM -0500, Steven Rostedt wrote: > On Sun, 25 Feb 2018 10:39:44 -0800 > "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote: > > > > Hmmm... Grasping at straws... Could we make cond_resched() be something > > > like a tracepoint and instrument them with cond_resched_rcu_qs() if the > > > current RCU-tasks grace period ran for more that (say) a minute of its > > > ten-minute stall-warning span? > > > > On the other hand, you noted in your other email that the tracepoint > > benchmark should not be enabled on production systems. So how about > > the following (again untested) patch? The "defined(CONFIG_TASKS_RCU)" > > might need to change, especially if RCU-tasks is used in production > > kernels, but perhaps a starting point. > > RCU tasks are used in production systems if PREEMPT is enabled (it > allows for optimizations with ftrace, perf and kprobes). > > But the tracepoint is not used.
Right, so I should use defined(CONFIG_TRACEPOINT_BENCHMARK) instead of defined(CONFIG_TASKS_RCU). Or am I misinterpreting the code in kernel/trace? > > ------------------------------------------------------------------------ > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index b161ef8a902e..316c29c5e506 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1589,6 +1589,12 @@ static inline int test_tsk_need_resched(struct > > task_struct *tsk) > > */ > > #ifndef CONFIG_PREEMPT > > extern int _cond_resched(void); > > +#elif defined(CONFIG_TASKS_RCU) > > +static inline int _cond_resched(void) > > +{ > > + rcu_note_voluntary_context_switch(current); > > + return 0; > > +} > > #else > > static inline int _cond_resched(void) { return 0; } > > #endif > > > This does work, but so does the below, without causing cond_resched() > from being something other than a nop of CONFIG_PREEMPT. True, but based on the cond_resched_rcu_qs() experience, I bet that trace_benchmark.c won't be the only place needing help. Thanx, Paul > -- Steve > > diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c > index 22fee766081b..82d83bb4874b 100644 > --- a/kernel/trace/trace_benchmark.c > +++ b/kernel/trace/trace_benchmark.c > @@ -166,6 +166,7 @@ static int benchmark_event_kthread(void *arg) > * block synchronize_rcu_tasks() indefinitely. > */ > cond_resched(); > + rcu_note_voluntary_context_switch(current); > } > > return 0; >