linux-kernel - Energy consumption oddity on a Mac-Mini

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Date:	Fri, 12 Feb 2016 11:50:32 +0300
From:	moosotc@...il.com
To:	linux-kernel@...r.kernel.org
Subject: Energy consumption oddity on a Mac-Mini


Hello,

Trying to make Linux consume as little(or less) power as OS X does on
this Mac mini (as measured by watt meter that sits between the box and
the power outlet) led me to the following sequence of commands:

[..start script..]
#!/bin/sh
set -e
test "$(id -u)" != "0" && exec sudo "$0" "$@"
echo powersave >/sys/module/pcie_aspm/parameters/policy
echo 1 >/sys/module/snd_hda_intel/parameters/power_save
echo min_power >/sys/class/scsi_host/host0/link_power_management_policy
echo 1 | tee >/dev/null /sys/bus/usb/devices/*/power/autosuspend
echo auto | tee >/dev/null /sys/devices/**/power/control

# Suspend to RAM only to restore in six seconds
# for some reason this step is essential here:
#    product: Macmini7,1 (System SKU#)
#    vendor: Apple Inc.
#    version: 1.0

echo +6 >/sys/class/rtc/rtc0/wakealarm
echo mem >/sys/power/state
echo 0 >/sys/class/rtc/rtc0/wakealarm
[..end script..]

Last 3 lines are the source of my confusion, why is this needed? The
situation is as follows:

* after boot the system consumes 8-9 watts
* with powertop(8) inspired sysfs tweaks but without the suspension 6-7
* with the suspend oscillating around 5-6

Would be nice to really know what's going on here. (My Linux-power-fu is
not too great)

-- 
mailto:moosotc@...il.com