[3.19.y-ckt stable] Patch "cpuidle: Fix cpuidle_state_is_coupled() argument in cpuidle_enter()" has been added to the 3.19.y-ckt tree

Kamal Mostafa kamal at canonical.com
Wed Jul 6 21:01:02 UTC 2016


This is a note to let you know that I have just added a patch titled

    cpuidle: Fix cpuidle_state_is_coupled() argument in cpuidle_enter()

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt23.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 6528723f5776240dde92fb72104d59185418e311 Mon Sep 17 00:00:00 2001
From: Daniel Lezcano <daniel.lezcano at linaro.org>
Date: Tue, 17 May 2016 16:54:00 +0200
Subject: cpuidle: Fix cpuidle_state_is_coupled() argument in cpuidle_enter()

commit e7387da52028b072489c45efeb7a916c0205ebd2 upstream.

Commit 0b89e9aa2856 (cpuidle: delay enabling interrupts until all
coupled CPUs leave idle) rightfully fixed a regression by letting
the coupled idle state framework to handle local interrupt enabling
when the CPU is exiting an idle state.

The current code checks if the idle state is coupled and, if so, it
will let the coupled code to enable interrupts. This way, it can
decrement the ready-count before handling the interrupt. This
mechanism prevents the other CPUs from waiting for a CPU which is
handling interrupts.

But the check is done against the state index returned by the back
end driver's ->enter functions which could be different from the
initial index passed as parameter to the cpuidle_enter_state()
function.

 entered_state = target_state->enter(dev, drv, index);

 [ ... ]

 if (!cpuidle_state_is_coupled(drv, entered_state))
	local_irq_enable();

 [ ... ]

If the 'index' is referring to a coupled idle state but the
'entered_state' is *not* coupled, then the interrupts are enabled
again. All CPUs blocked on the sync barrier may busy loop longer
if the CPU has interrupts to handle before decrementing the
ready-count. That's consuming more energy than saving.

Fixes: 0b89e9aa2856 (cpuidle: delay enabling interrupts until all coupled CPUs leave idle)
Signed-off-by: Daniel Lezcano <daniel.lezcano at linaro.org>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
[ kamal: backport to 3.19-stable: context ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/cpuidle/cpuidle.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 5a4ff9c..59dc6db 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -127,7 +127,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
 	time_end = ktime_get();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);

-	if (!cpuidle_state_is_coupled(dev, drv, entered_state))
+	if (!cpuidle_state_is_coupled(dev, drv, index))
 		local_irq_enable();

 	diff = ktime_to_us(ktime_sub(time_end, time_start));
--
2.7.4





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