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Message-ID: <20140721181527.GI8690@linux.vnet.ibm.com> Date: Mon, 21 Jul 2014 11:15:27 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, Viresh Kumar <viresh.kumar@...aro.org> Subject: Re: [PATCH 04/10] nohz: Appropriate timekeeper kick on sysidle break On Sat, Jul 19, 2014 at 02:44:15AM +0200, Frederic Weisbecker wrote: > When a CPU wakes up from idle and finds out that the timekeeper is > sleeping, we need to kick it such that it switches from dynticks to > periodic mode to maintain its timekeeping duty on behalf of the newly > awoken CPU. > > However we aren't using the right API for that. rcu_kick_nohz_cpu() is > aimed at waking full dynticks CPUs and not the timekeeper. > > Moreover the timekeeper must perform a new dynticks cycle to check the > new sysidle state and restart the tick if necessary. A simple call > to irq_exit() isn't enough. > > wake_up_nohz_cpu() is a good fit for that job because it pulls the > target out of the idle loop and restart the tick. Then if no other > task waits for the CPU, it will reenter the idle loop and then the > new sysidle state will be visible and well handled. > > Cc: Ingo Molnar <mingo@...nel.org> > Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Steven Rostedt <rostedt@...dmis.org> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Viresh Kumar <viresh.kumar@...aro.org> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> Either name is fine by me... ;-) Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > --- > kernel/rcu/tree_plugin.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 395c14d..b65da1a 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -2494,7 +2494,7 @@ void rcu_sysidle_force_exit(void) > oldstate, RCU_SYSIDLE_NOT); > if (oldstate == newoldstate && > oldstate == RCU_SYSIDLE_FULL_NOTED) { > - rcu_kick_nohz_cpu(tick_do_timer_cpu); > + wake_up_nohz_cpu(tick_do_timer_cpu); > return; /* We cleared it, done! */ > } > oldstate = newoldstate; > -- > 1.8.3.1 > > -- > 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/ > -- 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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