Messages in this thread Patch in this message | | | Date | Mon, 26 Feb 2018 21:29:20 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH tip/core/rcu 06/10] trace: Eliminate cond_resched_rcu_qs() in favor of cond_resched() |
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On Sun, 25 Feb 2018 10:39:44 -0800 "Paul E. McKenney" <paulmck@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.
> > 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;
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