Messages in this thread | | | Date | Sat, 2 Dec 2017 04:22:20 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in cond_resched() |
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On Sat, Dec 02, 2017 at 09:56:26AM +0100, Peter Zijlstra wrote: > On Fri, Dec 01, 2017 at 11:21:44AM -0800, Paul E. McKenney wrote: > > If cond_resched() returns false, then it has already invoked > > rcu_all_qs(). This is also invoked (now redundantly) by > > rcu_note_voluntary_context_switch(). This commit therefore changes > > cond_resched_rcu_qs() to invoke rcu_note_voluntary_context_switch_lite() > > instead of rcu_note_voluntary_context_switch() to avoid the redundant > > invocation of rcu_all_qs(). > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > --- > > include/linux/rcupdate.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index a6ddc42f87a5..7bd8b5a6db10 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -197,7 +197,7 @@ static inline void exit_tasks_rcu_finish(void) { } > > #define cond_resched_rcu_qs() \ > > do { \ > > if (!cond_resched()) \ > > - rcu_note_voluntary_context_switch(current); \ > > + rcu_note_voluntary_context_switch_lite(current); \ > > } while (0) > > > > Maybe I'm confused, but why are we keeping cond_resched_rcu_qs() around > at all?
Because there are a few key places within RCU and rcutorture that need it. Without it, there are scenarios where the new cond_resched() never gets activated, and thus doesn't take effect.
The key point is that with this series in place, it should not be necessary to use cond_resched_rcu_qs() outside of kernel/rcu and kernel/torture.c. Which is a valuable step forward, right?
Thanx, Paul
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