Messages in this thread | | | Date | Fri, 11 May 2018 12:25:28 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] rcu: Report a quiescent state when it's exactly in the state |
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On Fri, 11 May 2018 12:23:21 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 11 May 2018 09:17:46 -0700 > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > > > > >index ee8cf5fc..7432261 100644 > > > >--- a/include/linux/rcupdate.h > > > >+++ b/include/linux/rcupdate.h > > > >@@ -195,8 +195,8 @@ static inline void exit_tasks_rcu_finish(void) { } > > > > */ > > > > #define cond_resched_tasks_rcu_qs() \ > > > > do { \ > > > >- if (!cond_resched()) \ > > > >- rcu_note_voluntary_context_switch_lite(current); \ > > > >+ rcu_note_voluntary_context_switch_lite(current); \ > > > >+ cond_resched(); \ > > > > Ah, good point. > > > > Peter, I have to ask... Why is "cond_resched()" considered a preemption > > while "schedule()" is not? > > I would argue that cond_resched() not be considered a preemption. > Although, it may be called a "preemption point". A place that can be > preempted, but may not be. Maybe that's the answer. schedule() will > always schedule (even though it may pick the same task to run, but > not guaranteed to), where as, cond_resched() will only schedule if the > conditions are right. And maybe that's not really a "voluntary > schedule", although I think that can be argued against. >
I would also say that one should never call schedule() directly without changing its state to something other than TASK_RUNNING. Hence, calling schedule directly is saying you are ready to sleep. But that is not the case with cond_resched() which should always be called with the state as TASK_RUNNING.
-- Steve
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