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From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Byungchul Park <byungchul.park@lge.com>,
	jiangshanlai@gmail.com, josh@joshtriplett.org,
	mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org,
	kernel-team@lge.com, peterz@infradead.org
Subject: Re: [PATCH] rcu: Report a quiescent state when it's exactly in the state
Date: Fri, 11 May 2018 12:25:28 -0400	[thread overview]
Message-ID: <20180511122528.2a398d24@gandalf.local.home> (raw)
In-Reply-To: <20180511122321.722a12cc@gandalf.local.home>

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

  reply	other threads:[~2018-05-11 16:25 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-11  8:30 Byungchul Park
2018-05-11 12:57 ` Byungchul Park
2018-05-11 16:17   ` Paul E. McKenney
2018-05-11 16:23     ` Steven Rostedt
2018-05-11 16:25       ` Steven Rostedt [this message]
2018-05-11 16:27         ` Steven Rostedt
2018-05-11 17:27           ` Paul E. McKenney
2018-05-11 17:29             ` Steven Rostedt
2018-05-11 22:41     ` Joel Fernandes
2018-05-12  5:08       ` Paul E. McKenney
2018-05-12  6:30         ` Joel Fernandes
2018-05-12 14:41           ` Paul E. McKenney
2018-05-12 17:26             ` Steven Rostedt
2018-05-14  3:11               ` Byungchul Park
2018-05-13  0:09             ` Joel Fernandes
2018-05-14  2:59       ` Byungchul Park
2018-05-14 14:25         ` Byungchul Park
2018-05-14 21:04         ` Paul E. McKenney
2018-05-15  0:18           ` Byungchul Park

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