Messages in this thread Patch in this message | | | Date | Mon, 28 Nov 2011 16:39:31 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/4] rcu: Don't check irq nesting from rcu idle entry/exit |
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On Tue, Nov 29, 2011 at 01:26:01AM +0100, Frederic Weisbecker wrote: > On Mon, Nov 28, 2011 at 04:22:44PM -0800, Paul E. McKenney wrote: > > On Mon, Nov 28, 2011 at 10:24:44PM +0100, Frederic Weisbecker wrote: > > > rcu_idle_enter() and rcu_idle_exit() don't need to check > > > the irq nesting as they are not called from irq. > > > > > > Only check dyntick_nesting from rcu_irq_enter() and > > > rcu_irq_exit(). > > > > > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > > > Cc: Josh Triplett <josh@joshtriplett.org> > > > --- > > > kernel/rcutree.c | 18 ++++++++---------- > > > 1 files changed, 8 insertions(+), 10 deletions(-) > > > > I have queued this. I had to update it to deal with a recent conflicting > > update, please see below for the new version. > > > > Thanx, Paul > > Hmm, seems there is a problem. Look below:
Good eyes! How about the following instead?
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rcu: Don't check irq nesting from rcu idle entry/exit
Because tasks do not nest, rcu_idle_enter() and rcu_idle_exit() do not need to check for nesting. This commit therefore moves nesting checks from rcu_idle_enter_common() to rcu_irq_exit() and from rcu_idle_exit_common() to rcu_irq_enter().
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index bf085d7..860c02c 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -350,10 +350,6 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp) */ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval) { - if (rdtp->dynticks_nesting) { - trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting); - return; - } trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting); if (!is_idle_task(current)) { struct task_struct *idle = idle_task(smp_processor_id()); @@ -426,7 +422,10 @@ void rcu_irq_exit(void) oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting--; WARN_ON_ONCE(rdtp->dynticks_nesting < 0); - rcu_idle_enter_common(rdtp, oldval); + if (rdtp->dynticks_nesting) + trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting); + else + rcu_idle_enter_common(rdtp, oldval); local_irq_restore(flags); } @@ -439,10 +438,6 @@ void rcu_irq_exit(void) */ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) { - if (oldval) { - trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting); - return; - } smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */ atomic_inc(&rdtp->dynticks); /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ @@ -518,7 +513,10 @@ void rcu_irq_enter(void) oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting++; WARN_ON_ONCE(rdtp->dynticks_nesting == 0); - rcu_idle_exit_common(rdtp, oldval); + if (oldval) + trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting); + else + rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); }
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