Messages in this thread | | | Date | Mon, 14 May 2018 10:22:05 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC 2/8] rcu: Clarify usage of cond_resched for tasks-RCU |
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On Mon, May 14, 2018 at 10:54:54AM -0400, Steven Rostedt wrote: > On Sun, 13 May 2018 20:15:35 -0700 > "Joel Fernandes (Google)" <joel@joelfernandes.org> wrote: > > > Recently we had a discussion about cond_resched unconditionally > > recording a voluntary context switch [1]. > > > > Lets add a comment clarifying that how this API is to be used. > > > > [1] https://lkml.kernel.org/r/1526027434-21237-1-git-send-email-byungchul.park@lge.com > > > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > > --- > > include/linux/rcupdate.h | 11 ++++++++--- > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 743226176350..a9881007ece6 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -159,8 +159,12 @@ static inline void rcu_init_nohz(void) { } > > } while (0) > > > > /* > > - * Note a voluntary context switch for RCU-tasks benefit. This is a > > - * macro rather than an inline function to avoid #include hell. > > + * Note an attempt to perform a voluntary context switch for RCU-tasks benefit. > > + * > > + * This is called even in situations where a context switch didn't really > > + * happen even though it was requested. The caller uses it to indicate > > + * traversal of an RCU-tasks quiescent state. This is a macro rather than an > > + * inline function to avoid #include hell. > > I don't know. I just don't like the wording. It sounds too much like > it was written by someone that was confused for it being called when a > context switch didn't occur ;-) > > What about something more like: > > /* > * This is called to denote a RCU-task quiescent state. It is placed at > * voluntary preemption points, as RCU-task critical sections may not > * perform voluntary preemption or scheduling calls. It does not matter > * if the task is scheduled out or not, just that a voluntary preemption > * may be done. > */
s/RCU-task/RCU-tasks/ and I am good with this.
Thanx, Paul
> > */ > > #ifdef CONFIG_TASKS_RCU > > #define rcu_note_voluntary_context_switch_lite(t) \ > > @@ -187,7 +191,8 @@ static inline void exit_tasks_rcu_finish(void) { } > > #endif /* #else #ifdef CONFIG_TASKS_RCU */ > > > > /** > > - * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU > > + * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU. > > + * The quiescent state report is made even if cond_resched() did nothing. > > Same thing here. > > * The quiescent state report does not depend on cond_resched() scheduling. > > -- Steve > > > > * > > * This macro resembles cond_resched(), except that it is defined to > > * report potential quiescent states to RCU-tasks even if the cond_resched() >
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