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

["Doug Smythies" <dsmythies@telus.net>]

Does the direction that this thread has taken mean that those two
commits that Arto identified might now not be reverted?

Commits:
9c4b2867ed7c8c8784dd417ffd16e705e81eb145
a9ceb78bc75ca47972096372ff3d48648b16317a

Recall that increased energy consumption was also isolated to those
two commits for some types of workflow. The suggestion is that the
commits should be reverted anyhow.

What seems to be happening is that CPUs are deciding to stay in idle
state 0 a lot more, when they actually could / should be in a deeper
idle state.

Test time is always: 33 minutes and 20 seconds test (8 CPUs), and there
is never any noticeable difference in execution times for the work:

Example 1: kernel 4.5-rc5 with the rjw 3 patch set version 10
"Replace timers with utilization update callbacks":
Aggregate times in each idle state:

rjwv10 (minutes)	reverted (minutes)	Idle State
27.0654211		2.617325533			0
12.92451315		24.53266672			1
3.668558467		3.780482633			2
1.2727832		1.61352195			3
130.8342596		141.2234947			4
		
175.7655355		173.7674915			total

Example 2: kernel 4.5-rc7 stock:
Aggregate times in each idle state:

k45rc7 (minutes)	reverted (minutes)	Idle State
20.1771917		2.638311483			0
13.02770225		21.81474838			1
3.428136783		3.951405			2
1.4540243		1.552488167			3
134.9057413		143.5533			4
		
172.9927963		173.5102531			total

Energy (restated from a previous e-mail):

Test 7: reverted: Package Joules: 47830
Test 8: rjwv10: Package Joules: 54419 (revert saves 12.1% energy)

Test 9: reverted: Package Joules: 49326
Test 10: rjwv10: Package Joules: 55442 (revert saves 11% energy)

Test 11: reverted: acpi-cpufreq ondemand: Package Joules: 49146
Test 12: rjwv10: acpi-cpufreq ondemand: Package Joules: 56302 (revert saves 12.7% energy)

Energy (not in any previous e-mail):

Reverted: 56178 Joules
Kernel 4.5-rc7: 63269 Joules (revert saves 12.6% energy)

Note 1: The test computer was rebuilt in between old and new tests,
so the baseline energy may have changed.

Note 2: Unless otherwise stated, intel_pstate driver, powersave governor.

... Doug