On 09/15/2014 12:29 PM, Michael Ellerman wrote:

On Fri, 2014-09-12 at 16:31 +0530, Preeti U Murthy wrote:

quoted

Today the procfs interface /proc/sys/kernel/powersave-nap is used to control
entry into deep idle states beyond snooze. Check for the value of this
parameter before entering fastsleep. We already do this check for nap in
power7_idle().

Signed-off-by: Preeti U Murthy <redacted>
---

 drivers/cpuidle/cpuidle-powernv.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index a64be57..b8ba52e 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c

@@ -69,6 +69,12 @@ static int fastsleep_loop(struct cpuidle_device *dev,
 	unsigned long old_lpcr = mfspr(SPRN_LPCR);
 	unsigned long new_lpcr;
 
+	/*
+	 * Verify if snooze is the only valid cpuidle state
+	 */
+	if (!(powersave_nap > 0))
+		return index;
+
 	if (unlikely(system_state < SYSTEM_RUNNING))
 		return index;

Doesn't the above mean we are just going to keep trying to go into fastsleep
again and again? Or does the idle code work out that it didn't work based on
the fact that we didn't sleep for the right period?

Thats right. The idle code figures that its judgment to enter fastsleep
was not correct and applies a correction factor to its future decisions
. This correction factor is intended to influence the cpuidle governor's
decision on choosing an idle state for the cpu based on the history of
wakeups. Hence a shallower idle state will be chosen here on in the
above circumstance.

We were talking about getting rid of powersave_nap altogether, but I think we
decided we couldn't, I forget.

Isn't this a helpful knob to disable cpuidle at runtime? Currently we
check the value of powersave_nap before entering both nap and fastsleep.

Regards
Preeti U Murthy

cheers


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