linux-kernel - Re: [PATCH] rcu: Report a quiescent state when it's exactly in the state

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Message-Id: <20180511172735.GB26088@linux.vnet.ibm.com>
Date:   Fri, 11 May 2018 10:27:35 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Byungchul Park <byungchul.park@....com>, jiangshanlai@...il.com,
        josh@...htriplett.org, mathieu.desnoyers@...icios.com,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        peterz@...radead.org
Subject: Re: [PATCH] rcu: Report a quiescent state when it's exactly in the
 state

On Fri, May 11, 2018 at 12:27:12PM -0400, Steven Rostedt wrote:
> On Fri, 11 May 2018 12:25:28 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > 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.
> 
> To continue this, with tracing, when a task is scheduled out in the
> RUNNING state, it is considered preempted, otherwise it is not.

I suppose another option would be for cond_resched_tasks_rcu_qs() to set
(and later clear) a per-CPU variable that causes rcu_note_context_switch()
to ignore its "preempt" parameter.  Byungchul's approach seems more
straightforward, though.

							Thanx, Paul