Active State Power Management In Linux

Issue

Ever felt that your laptop is draining battery in linux faster than windows??? This could be because of ASPM disabled… Its a topic which is very important for linux beginners often not told. Especially if you are running a hardware only made to run windows. This could be the reason behind poor laptop battery saving in linux.

run

dmesg | grep fail

Introduction

Active State Power Management(ASPM) is a PCI-E enhancement. It allows for a device to go completely into electrically idle state, meaning it will not send or receive electrical signals for a while. To achieve this the PCI-E specification has come up with instructions a PCI-E endpoint (device) should follow for signaling to a root complex (the bus) that it is going idle, or waking up. Communication at the PCI-E bus can be tricky to align with an endpoint and because of this there are patterns a PCI-E device will use to train the link to come out of electrical idle states. There are several states a device will enter when using ASPM, namely L1, L0s.

PCIE cards should always support ASPM, what the ASPM requirements says today is that L1 is mandatory and L0s is optional unless the formfactor specifications explicitly requies it. Not sure which form factors explicitly require L0s (anyone?). Additionally software must not enable L0s in either direction on a given Link unless components on both sides of the Link each support L0s.

The way it typically works internally on endpoints (devices) is that there are idle timers (counters) in the chipset. There is a set point at which the PCIe link is idle enough to enter L0s, and a second point at which we’re idle enough to enter L1. A device could potentially ‘support’ L0s but internally the timers could be set such that L0s and L1 happen at the same time or L0s happens after L1, so the link will essentially never enter L0s. ASPM compliance may vary by device, ASPM specification has varied as new releases have been made.

Its normally not a thing an OS plays with but should be handled by BIOS. The problem is that motherboard vendors mostly only design for windows. So in case that your motherboard does not have any options, you can atleast have linux kernel overpower the BIOS. A warning though, only do this if you are absolutely sure that your device does support ASPM. PCIE requires ASPM but L0s are optional (so L0s might be disabled and only L1 enabled). Forcing on ASPM can cause a freeze/panic in case its not supported. And while This forces ASPM in kernel, it can still remain disabled in hardware and not work.

Here, I will assume you use grub bootloader. If you use other bootloader, follow accordingly.

First, on your /etc/default/grub, in the line GRUB_CMDLINE_LINUX_DEFAULT add pcie_aspm=force. Or pass it as a kernel parameter in your bootloader if you dont use grub.

Then run update-grub or grub-mkconfig -o /boot/grub/grub.cfg depending on your distribution and reboot.

Now, on your terminal, type the command lspci -vvv as root. You will get a long list of various devices. Check along the lines of LnkCtl and note if ASPM is enabled for all devices or not. Also note the number before the name of device something like 04:00.0 which is the End point. Note the name of the device and its respective endpoint.

You also need the root complex of the device. For that, run lspci -tnvv Tally the name of the device of certain endpoint to find its root complex. If its +-14.2, ignore +- and take 00:14.2 as the root complex. (00: at first) Some device may only have either root complex or end point.

Now, install setpci and bc packages like

apt-get install setpci bc

if they werent installed

Now, get the handy script at the end of this article and make it run as root every time the system boots. The script is well commented and so you may not have any problem… You do need to edit it as per your root complex and endpoint for the device you want to enable ASPM.

Note that only the last root complex and last endpoint is not commented. For me, I had to make the same script execute three times by copy-pasting entire script one after another for each device. And only the last endpoint and last root complex was considered each time the script ran. Execute the script yourself as root before making it run on boot automatically to ensure you have correctly edited the script and it works. It will print success messages on screen.

Learn More

kernel.org article

Active State Power Management in Wikipedia

TonyMac86 - Despite being for Mac, it is equally relevant

ArchWiki Power Management

Potential issues

• Your USB devices may misbehave

Script

#!/bin/bash
# Copyright (c) 2010-2013 Luis R. Rodriguez <mcgrof@do-not-panic.com>
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.


# ASPM Tuning script
#
# This script lets you enable ASPM on your devices in case your BIOS
# does not have it enabled for some reason. If your BIOS does not have
# it enabled it is usually for a good reason so you should only use this if
# you know what you are doing. Typically you would only need to enable
# ASPM manually when doing development and using a card that typically
# is not present on a laptop, or using the cardbus slot. The BIOS typically
# disables ASPM for foreign cards and on the cardbus slot. Check also
# if you may need to do other things than what is below on your vendor
# documentation.
#
# To use this script You will need for now to at least query your device
# PCI endpoint and root complex addresses using the convention output by
# lspci: [<bus>]:[<slot>].[<func>]
#
# For example:
#
# 03:00.0 Network controller: Atheros Communications Inc. AR9300 Wireless LAN adaptor (rev 01
# 00:1c.1 PCI bridge: Intel Corporation 82801H (ICH8 Family) PCI Express Port 2 (rev 03)
#
# The root complex for the endpoint can be found using lspci -t
#
# For more details refer to:
#
# http://wireless.kernel.org/en/users/Documentation/ASPM

# You just need to modify these three values:

#ROOT_COMPLEX="00:1c.1"
#ROOT_COMPLEX="00:1e.0"
ROOT_COMPLEX="00:1c.3"
#ENDPOINT="03:00.0"
#ENDPOINT="05:00.0"
ENDPOINT="05:00.0"

# We'll only enable the last 2 bits by using a mask
# of :3 to setpci, this will ensure we keep the existing
# values on the byte.
#
# Hex  Binary  Meaning
# -------------------------
# 0    0b00    L0 only
# 1    0b01    L0s only
# 2    0b10    L1 only
# 3    0b11    L1 and L0s
ASPM_SETTING=3

function aspm_setting_to_string()
{
	case $1 in
	0)
		echo -e "\t${BLUE}L0 only${NORMAL}, ${RED}ASPM disabled${NORMAL}"
		;;
	1)
		;;
	2)
		echo -e "\t${GREEN}L1 only${NORMAL}"
		;;
	3)
		echo -e "\t${GREEN}L1 and L0s${NORMAL}"
		;;
	*)
		echo -e "\t${RED}Invalid${NORMAL}"
		;;
	esac
}


###################################################################
# Do not edit below here unless you are sending me a patch
###################################################################
#
# TODO: patches are welcomed to me until we submit to to
#       PCI Utilities upstream.
#
# This can be improved by in this order:
#
#	* Accept arguments for endpoint and root complex address, and
#	  desired ASPM settings
#	* Look for your ASPM capabilities by quering your
#	  LnkCap register first. Use these values to let you
#	  select whether you want to enable only L1 or L1 & L0s
#	* Searching for your root complex for you
#	* Search for your PCI device by using the driver
#	* Disable your driver and ask to reboot ?
#	* Rewrite in C
#	* Write ncurses interface [ wishlist ]
#	* Write GTK/QT interface [ wishlist ]
#	* Submit upstream as aspm.c to the PCI Utilities, which are
#	  maintained by Martin Mares <mj@ucw.cz>

# Pretty colors
GREEN="\033[01;32m"
YELLOW="\033[01;33m"
NORMAL="\033[00m"
BLUE="\033[34m"
RED="\033[31m"
PURPLE="\033[35m"
CYAN="\033[36m"
UNDERLINE="\033[02m"

# we can surely read the spec to get a better value
MAX_SEARCH=20
SEARCH_COUNT=1
ASPM_BYTE_ADDRESS="INVALID"

ROOT_PRESENT=$(lspci | grep -c "$ROOT_COMPLEXT")
ENDPOINT_PRESENT=$(lspci | grep -c "$ENDPOINT")

if [[ $(id -u) != 0 ]]; then
	echo "This needs to be run as root"
	exit 1
fi

if [[ $ROOT_PRESENT -eq 0 ]]; then
	echo "Root complex $ROOT_COMPLEX is not present"
	exit
fi

if [[ $ENDPOINT_PRESENT -eq 0 ]]; then
	echo "Endpoint $ENDPOINT is not present"
	exit
fi

# XXX: lspci -s some_device_not_existing does not return positive
# if the device does not exist, fix this upstream
function device_present()
{

	PRESENT=$(lspci | grep -c "$1")
	COMPLAINT="${RED}not present${NORMAL}"

	if [[ $PRESENT -eq 0 ]]; then
		if [[ $2 != "present" ]]; then
			COMPLAINT="${RED}disappeared${NORMAL}"
		fi

		echo -e "Device ${BLUE}${1}${NORMAL} $COMPLAINT" 
		return 1
	fi
	return 0
}

function find_aspm_byte_address()
{
	device_present $ENDPOINT present
	if [[ $? -ne 0 ]]; then
		exit
	fi

	SEARCH=$(setpci -s $1 34.b)
	# We know on the first search $SEARCH will not be
	# 10 but this simplifies the implementation.
	while [[ $SEARCH != 10 && $SEARCH_COUNT -le $MAX_SEARCH ]]; do
		END_SEARCH=$(setpci -s $1 ${SEARCH}.b)

		# Convert hex digits to uppercase for bc
		SEARCH_UPPER=$(printf "%X" 0x${SEARCH})

		if [[ $END_SEARCH = 10 ]]; then
			ASPM_BYTE_ADDRESS=$(echo "obase=16; ibase=16; $SEARCH_UPPER + 10" | bc)
			break
		fi

		SEARCH=$(echo "obase=16; ibase=16; $SEARCH + 1" | bc)
		SEARCH=$(setpci -s $1 ${SEARCH}.b)

		let SEARCH_COUNT=$SEARCH_COUNT+1
	done

	if [[ $SEARCH_COUNT -ge $MAX_SEARCH ]]; then
		echo -e "Long loop while looking for ASPM word for $1"
		return 1
	fi
	return 0
}

function enable_aspm_byte()
{
	device_present $1 present
	if [[ $? -ne 0 ]]; then
		exit
	fi

	find_aspm_byte_address $1
	if [[ $? -ne 0 ]]; then
		return 1
	fi

	ASPM_BYTE_HEX=$(setpci -s $1 ${ASPM_BYTE_ADDRESS}.b)
	ASPM_BYTE_HEX=$(printf "%X" 0x${ASPM_BYTE_HEX})
	# setpci doesn't support a mask on the query yet, only on the set,
	# so to verify a setting on a mask we have no other optoin but
	# to do do this stuff ourselves.
	DESIRED_ASPM_BYTE_HEX=$(printf "%X" $(( (0x${ASPM_BYTE_HEX} & ~0x7) |0x${ASPM_SETTING})))

	if [[ $ASPM_BYTE_ADDRESS = "INVALID" ]]; then
		echo -e "No ASPM byte could be found for $(lspci -s $1)"
		return
	fi

	echo -e "$(lspci -s $1)"
	echo -en "\t${YELLOW}0x${ASPM_BYTE_ADDRESS}${NORMAL} : ${CYAN}0x${ASPM_BYTE_HEX}${GREEN} --> ${BLUE}0x${DESIRED_ASPM_BYTE_HEX}${NORMAL} ... "

	device_present $1 present
	if [[ $? -ne 0 ]]; then
		exit
	fi

	# Avoid setting if already set
	if [[ $ASPM_BYTE_HEX = $DESIRED_ASPM_BYTE_HEX ]]; then
		echo -e "[${GREEN}SUCESS${NORMAL}] (${GREEN}already set${NORMAL})"
		aspm_setting_to_string $ASPM_SETTING
		return 0
	fi

	# This only writes the last 3 bits
	setpci -s $1 ${ASPM_BYTE_ADDRESS}.b=${ASPM_SETTING}:3

	sleep 3

	ACTUAL_ASPM_BYTE_HEX=$(setpci -s $1 ${ASPM_BYTE_ADDRESS}.b)
	ACTUAL_ASPM_BYTE_HEX=$(printf "%X" 0x${ACTUAL_ASPM_BYTE_HEX})

	# Do not retry this if it failed, if it failed to set.
	# Likey if it failed its a good reason and you should look
	# into that.
	if [[ $ACTUAL_ASPM_BYTE_HEX != $DESIRED_ASPM_BYTE_HEX ]]; then
		echo -e "\t[${RED}FAIL${NORMAL}] (0x${ACTUAL_ASPM_BYTE_HEX})"
		return 1
	fi

	echo -e "\t[${GREEN}SUCCESS]${NORMAL}]"
	aspm_setting_to_string $ASPM_SETTING

	return 0
}

device_present $ENDPOINT not_sure
if [[ $? -ne 0 ]]; then
	exit
fi

echo -e "${CYAN}Root complex${NORMAL}:"
enable_aspm_byte $ROOT_COMPLEX
echo

echo -e "${CYAN}Endpoint${NORMAL}:"
enable_aspm_byte $ENDPOINT
echo