Re: SKL BOOT FAILURE unless idle=nomwait (was Re: PROBLEM: Cpufreq constantly keeps frequency at maximum on 4.5-rc4)

[Rik van Riel <riel@redhat.com>]

On Fri, 11 Mar 2016 10:22:30 -0800
"Doug Smythies" <dsmythies@telus.net> wrote:

> On 2016.03.11 06:03 Rik van Riel wrote:
> > On Thu, 10 Mar 2016 00:59:01 +0100 "Rafael J. Wysocki" <rafael@kernel.org> wrote:

> > The patch below should fix that.
> >
> > It didn't for Arto, due to the other issues on his system, but
> > it might resolve the issue for Doug, where cstate/pstate is
> > otherwise working fine.
> >
> > Doug, does the patch below solve your issue?
> 
> No.

OK, lets try doing this check a little more aggressively, since there
almost certainly are good reasons why the main selection loop in
menu_select() so aggressively tries to stay with shallower C states.

With the patch below, we compare the (not corrected for load) expected
sleep time against the target residency of the C1 (hlt) state on the CPU.

This might resolve the issue, while still doing the right thing on CPUs
that have really high C1 latencies (eg. Atom).

Does this resolve the issue for you?

---8<---

Subject: cpuidle: use predicted_us not interactivity_req to consider polling

The interactivity_req variable is the expected sleep time, divided
by the CPU load. This can be too aggressive a factor in deciding
whether or not to consider polling in the cpuidle state selection.

Use the (not corrected for load) predicted_us instead, and compare
it against the target residency of C1 (hlt).

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 drivers/cpuidle/governors/menu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 0742b3296673..7dda15cfe547 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -330,7 +330,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 		 * We want to default to C1 (hlt), not to busy polling
 		 * unless the timer is happening really really soon.
 		 */
-		if (interactivity_req > 20 &&
+		if (data->predicted_us > drv->states[CPUIDLE_DRIVER_STATE_START].target_residency &&
 		    !drv->states[CPUIDLE_DRIVER_STATE_START].disabled &&
 			dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0)
 			data->last_state_idx = CPUIDLE_DRIVER_STATE_START;