linux-kernel - Re: [PATCH][RFC] PM / s2idle: Clear _TIF_POLLING

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Date:   Mon, 15 Jun 2020 21:31:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] PM / s2idle: Clear _TIF_POLLING_NRFLAG before
 suspend to idle

On Mon, Jun 15, 2020 at 08:40:41PM +0200, Peter Zijlstra wrote:

> > @@ -186,8 +187,10 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> >  	 * be frozen safely.
> >  	 */
> >  	index = find_deepest_state(drv, dev, U64_MAX, 0, true);
> > -	if (index > 0)
> > +	if (index > 0) {
> > +		__current_clr_polling();
> >  		enter_s2idle_proper(drv, dev, index);
> > +	}
> >  
> >  	return index;
> >  }
> 
> So how is that commit 08e237fa56a1 not suffient? That makes
> mwait_idle_with_hints() DTRT for this 'functionally challenged' piece of
> hardware.
> 
> AFAICT intel_enter_s2idle() uses mwait_idle_with_hints().
> 
> What am I missing?

What's missing is that cpuidle_enter_s2idle() doesn't properly match
call_cpuidle().

Something like so then. Your version is racy, if someone already set
TIF_NEED_RESCHED you just clear POLLING and go to sleep.

---

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index c149d9e20dfd..81bee8d03c6d 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -133,8 +133,8 @@ int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
 }
 
 #ifdef CONFIG_SUSPEND
-static void enter_s2idle_proper(struct cpuidle_driver *drv,
-				struct cpuidle_device *dev, int index)
+static void s2idle_enter(struct cpuidle_driver *drv,
+			 struct cpuidle_device *dev, int index)
 {
 	ktime_t time_start, time_end;
 
@@ -168,6 +168,15 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
 	dev->states_usage[index].s2idle_usage++;
 }
 
+static int call_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
+		       int index)
+{
+	if (!current_clr_polling_and_test())
+		s2idle_enter(drv, dev, index);
+
+	return index;
+}
+
 /**
  * cpuidle_enter_s2idle - Enter an idle state suitable for suspend-to-idle.
  * @drv: cpuidle driver for the given CPU.
@@ -187,7 +196,7 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	 */
 	index = find_deepest_state(drv, dev, U64_MAX, 0, true);
 	if (index > 0)
-		enter_s2idle_proper(drv, dev, index);
+		call_s2idle(drv, dev, index);
 
 	return index;
 }