linux-kernel - Re: [PATCH v2 1/6] idle: move the cpuidle entry point to the generic idle loop

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Date:	Wed, 29 Jan 2014 15:31:36 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Olof Johansson <olof@...om.net>,
	Russell King <linux@....linux.org.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
cc:	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/6] idle: move the cpuidle entry point to the generic
 idle loop

On Wed, 29 Jan 2014, Nicolas Pitre wrote:

> In order to integrate cpuidle with the scheduler, we must have a better
> proximity in the core code with what cpuidle is doing and not delegate
> such interaction to arch code.
> 
> Architectures implementing arch_cpu_idle() should simply enter
> a cheap idle mode in the absence of a proper cpuidle driver.
> 
> Signed-off-by: Nicolas Pitre <nico@...aro.org>
> Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>

As mentioned in my reply to Olof's comment on patch #5/6, here's a new 
version of this patch adding the safety local_irq_enable() to the core 
code.

----- >8

From: Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: idle: move the cpuidle entry point to the generic idle loop

In order to integrate cpuidle with the scheduler, we must have a better
proximity in the core code with what cpuidle is doing and not delegate
such interaction to arch code.

Architectures implementing arch_cpu_idle() should simply enter
a cheap idle mode in the absence of a proper cpuidle driver.

In both cases i.e. whether it is a cpuidle driver or the default
arch_cpu_idle(), the calling convention expects IRQs to be disabled
on entry and enabled on exit. There is a warning in place already but
let's add a forced IRQ enable here as well.  This will allow for
removing the forced IRQ enable some implementations do locally and 
allowing for the warning to trig.

Signed-off-by: Nicolas Pitre <nico@...aro.org>

diff --git a/kernel/cpu/idle.c b/kernel/cpu/idle.c
index 988573a9a3..14ca43430a 100644
--- a/kernel/cpu/idle.c
+++ b/kernel/cpu/idle.c
@@ -3,6 +3,7 @@
  */
 #include <linux/sched.h>
 #include <linux/cpu.h>
+#include <linux/cpuidle.h>
 #include <linux/tick.h>
 #include <linux/mm.h>
 #include <linux/stackprotector.h>
@@ -95,8 +96,10 @@ static void cpu_idle_loop(void)
 				if (!current_clr_polling_and_test()) {
 					stop_critical_timings();
 					rcu_idle_enter();
-					arch_cpu_idle();
-					WARN_ON_ONCE(irqs_disabled());
+					if (cpuidle_idle_call())
+						arch_cpu_idle();
+					if (WARN_ON_ONCE(irqs_disabled()))
+						local_irq_enable();
 					rcu_idle_exit();
 					start_critical_timings();
 				} else {
--
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