On Sun, 25 Feb 2018 10:39:44 -0800
"Paul E. McKenney" <[email protected]> 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.
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> 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.
-- 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;
