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14 September 2017 @ 09:23 am
Improving Linux laptop battery life: Testers Wanted  
Edit: linrunner (TLP author) has been so kind as to make prebuilt Ubuntu kernel packages with the patch available.

My next project for Red Hat is to work on improving Linux laptop battery life. Part of the (hopefully) low hanging fruit here is using kernel tunables to enable more runtime powermanagement. My first target here is SATA Link Power Management (LPM) which, as Matthew Garrett blogged about 2 years ago, can lead to a significant improvement in battery life.

There is only one small problem, there have been some reports that some disks/SSDs don't play well with Linux' min_power LPM policy and that this may lead to system crashes and even data corruption.

Let me repeat this: Enabling SATA LPM may lead to DATA CORRUPTION. So if you want to help with testing this please make sure you have recent backups! Note this happens only in rare cases (likely only with a coupe of specific SSD models with buggy firmware. But still DATA CORRUPTION may happen make sure you have BACKUPS.

As part of his efforts 2 years ago Matthew found this document which describes the LPM policy the Windows Intel Rapid Storage Technology (IRST) drivers use by default and most laptops ship with these drivers installed.

So based on an old patch from Matthew I've written a patch adding support for a new LPM policy called "med_power_with_dipm" to Linux. This saves
(almost) as much power as the min_power setting and since it matches Windows defaults I hope that it won't trip over any SSD/HDD firmware bugs.

So this is where my call for testers comes in, for Fedora 28 we would like to switch to this new SATA LPM policy by default (on laptops at least), but
we need to know that this is safe to do. So we are looking for people to help test this, if you have a laptop with a SATA drive (not NVME) and would like to help please make BACKUPS and then continue reading :)

First of all on a clean Fedora (no powertop --auto-tune, no TLP) do "sudo dnf install powertop", then close all your apps except for 1 terminal, maximimze that terminal and run "sudo powertop".

Now wait 5 minutes, on some laptops the power measurement is a moving average so this is necessary to get a reliable reading. Now look at the
power consumption shown (e.g. 7.95W), watch it for a couple of refreshes as it sometimes spikes when something wakes up to do some work, write down the lowest value you see, this is our base value for your laptops power consumption.

Next install the new kernel and try the new SATA LPM policy. I've done a scratch-build of the Fedora kernel with this patch added, which
you can download here. Linrunner (TLP author) has been so kind as to make prebuilt Ubuntu kernel packages with the patch available.

After downloading all the .x86_64.rpm files there into a dir, do from this dir:
sudo rpm -ivh kernel*.x86_64.rpm

Next download a rc.local script applying the new settings from here, copy it to /etc/rc.d/rc.local, and make it executable: "sudo chmod +x /etc/rc.d/rc.local".

Now reboot and do: "cat /sys/class/scsi_host/host0/link_power_management_policy" this should return med_power_with_dipm, if not something is wrong.

Then close all your apps except for 1 terminal, maximimze that terminal and run "sudo powertop" again. Wait 5 minutes as last time, then get a couple of readings and write down the lowest value you see.

After this continue using your laptop as normal, please make sure that you keep running the special kernel with the patch adding the "med_power_with_dipm" policy. If after 2 weeks you've not noticed any bad side effects (or if you do notice bad side effects earlier) send me a mail at hdegoede@redhat.com with:

  • Report of success or bad side effects

  • The idle powerconsumption before and after the changes

  • The brand and model of your laptop

  • The output of the following commands:

  • cat /proc/cpuinfo | grep "model name"

  • cat /sys/class/scsi_device/*/device/model

I will gather the results in a table which will be part of the to-be-created Fedora 28 Changes page for this.

Did I mention already that although the chance is small something will go wrong, it is non zero and you should create backups ?

Thank you for your time.
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