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Date: Tue, 6 Oct 2015 14:05:39 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Josh Triplett <josh@...htriplett.org>, linux-kernel@...r.kernel.org, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com, Boqun Feng <boqun.feng@...il.com> Subject: Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers On Tue, Oct 06, 2015 at 10:52:00PM +0200, Peter Zijlstra wrote: > On Tue, Oct 06, 2015 at 01:18:01PM -0700, Paul E. McKenney wrote: > > On Tue, Oct 06, 2015 at 10:05:38PM +0200, Peter Zijlstra wrote: > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > index b9d9e0249e2f..93c0f23c3e45 100644 > > > > --- a/kernel/rcu/tree.c > > > > +++ b/kernel/rcu/tree.c > > > > @@ -337,12 +337,14 @@ static void rcu_momentary_dyntick_idle(void) > > > > */ > > > > void rcu_note_context_switch(void) > > > > { > > > > + barrier(); /* Avoid RCU read-side critical sections leaking down. */ > > > > trace_rcu_utilization(TPS("Start context switch")); > > > > rcu_sched_qs(); > > > > rcu_preempt_note_context_switch(); > > > > if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) > > > > rcu_momentary_dyntick_idle(); > > > > trace_rcu_utilization(TPS("End context switch")); > > > > + barrier(); /* Avoid RCU read-side critical sections leaking up. */ > > > > } > > > > EXPORT_SYMBOL_GPL(rcu_note_context_switch); > > > > > > These OTOH could be fixed with a noinline, such that the compiler may > > > never inline it, even with whole-program-optimizations, thereby > > > guaranteeing a function call boundary or compiler barrier. > > > > I like the barrier() with the comment. I expect it will be a bit more > > robust against toolchain changes. > > Don't you in fact already rely on the fact that schedule() is a function > call and will not be inlined? (it doesn't have noinline and I suppose > whole program optimizers could go funny on it). Probably pretty much everywhere I call schedule(). But I was thinking that barrier() and the beginning and end of an external function didn't need to do anything. Is that incorrect? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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