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Date: Tue, 11 Jul 2017 05:58:47 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Aubrey Li <aubrey.li@...el.com> Cc: tglx@...utronix.de, peterz@...radead.org, len.brown@...el.com, rjw@...ysocki.net, ak@...ux.intel.com, tim.c.chen@...ux.intel.com, arjan@...ux.intel.com, yang.zhang.wz@...il.com, x86@...nel.org, linux-kernel@...r.kernel.org, Aubrey Li <aubrey.li@...ux.intel.com>, fweisbec@...il.com Subject: Re: [RFC PATCH v1 04/11] sched/idle: make the fast idle path for short idle periods On Mon, Jul 10, 2017 at 09:38:34AM +0800, Aubrey Li wrote: > From: Aubrey Li <aubrey.li@...ux.intel.com> > > The system will enter a fast idle loop if the predicted idle period > is shorter than the threshold. > --- > kernel/sched/idle.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index cf6c11f..16a766c 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -280,6 +280,8 @@ static void cpuidle_generic(void) > */ > static void do_idle(void) > { > + unsigned int predicted_idle_us; > + unsigned int short_idle_threshold = jiffies_to_usecs(1) / 2; > /* > * If the arch has a polling bit, we maintain an invariant: > * > @@ -291,7 +293,12 @@ static void do_idle(void) > > __current_set_polling(); > > - cpuidle_generic(); > + predicted_idle_us = cpuidle_predict(); > + > + if (likely(predicted_idle_us < short_idle_threshold)) > + cpuidle_fast(); What if we get here from nohz_full usermode execution? In that case, if I remember correctly, the scheduling-clock interrupt will still be disabled, and would have to be re-enabled before we could safely invoke cpuidle_fast(). Or am I missing something here? Thanx, Paul > + else > + cpuidle_generic(); > > __current_clr_polling(); > > -- > 2.7.4 >
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