[HowTo] Enable A72 cores to make Xperia ~1.7x faster

asked 2018-08-02 14:16:06 +0300

butler gravatar image

updated 2018-08-03 11:40:14 +0300

jiit gravatar image

TLDR: unconditionally enable fast cores to get 40% decrease in app load times and 1.7x speedup in exchange for battery life. Also see warning below.

Xperia's MSM8956 CPU has 2 fast A72 cores and 4 slower low-power A53 cores. Default kernel scheduler powers up faster cores only if all 4 slower cores are loaded with work, and it's very rare occurence to load 4 cores on a phone, so A72s usually stay disabled. It's a known problem, and I think here on TJC sailors said that they won't do ad-hoc fixes and will wait for newer 4.x kernel integration into Sailfish. It's supposed to have better scheduling policies and to solve this problem without extra work from Jolla.

I happened to run a small computational problem yesterday, and noticed that faster cores are actually 2-3x faster. This potential shouldn't be wasted! Well, raw computational power doesn't translate 1:1 to faster load times. So I did a small benchmark with firefox for android and measured time it takes from tap on screen to fully loaded browser with homepage tab opened (meaning it's loaded, screen finished updating; tab doesn't load any site and shouldn't do network access). To time it, I recorded the process on my PC's webcam and counted frames afterwards. On slower cores it takes 83 frames, on faster cores 48 frames at 30fps (2.7s vs 1.6s). So it's 1 second faster, 1.7x more performance, 40% load time reduction. This benchmark is far from robust, but I guess it shows potential and what to expect.

Below is the script to set scheduler into manual mode. Use sudo ./cpu.sh fast to enable only fast cores and disable slow ones. Set param to all to enable all, slow to leave only slow cores running, and default to revert to the initial state. First save the script somewhere as cpu.sh, run chmod 755 cpu.sh to make it executable.

Warning: Use at your own risk! Turning on fast cores will reduce battery time, I haven't measured the effect yet. Occasionally running the script causes immidiate reboot, and unexpected reboots can damage filesystem. Though if reboot didn't happen, system seems stable afterwards. I'm going to leave cpu of my phone in the fast mode, and see how it goes.



function switch_cores {

        for c in "$@"; do
                if [ "$(cat $fname)" != "$state" ]; then
                        echo $state >$fname

case "$1" in
        echo userspace >$GOVERNOR
        switch_cores 1  4 5
        switch_cores 0  0 1 2 3
        echo userspace >$GOVERNOR
        switch_cores 1  0 1 2 3
        switch_cores 0  4 5
        echo userspace >$GOVERNOR
        switch_cores 1  0 1 2 3 4 5
        echo rqbalance >$GOVERNOR
        echo "Usage: $0 [fast|slow|all|default]"
        exit -1

echo "governor:" $(cat $GOVERNOR)
for c in 0 1 2 3 4 5; do
        echo "core $c:"  $(cat /sys/devices/system/cpu/cpu$c/online)

Edit: code formatting & TLDR & fix title & fix grammar

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maybe if this problem ist solved, the Xperias don't get hot as hell anymore when playing some android games. I can imagine, that its not so healthy in long term.

Raymaen ( 2018-08-02 16:18:51 +0300 )edit

Nice Share man, useful info for when I do get my hands on my Xperia, kudos once again.

DameCENO ( 2018-08-02 16:32:48 +0300 )edit

@Raymaen likely it'll get only worse. As I understand currently A72 cores are turned off except in some very special circumstances. If a game eats as much CPU as it's allowed to, and Jolla turns on A72 cores for foreground processes, CPU will heat even more. Possible fix is to throttle when temperature gets too high, but that's another mechanism that needs tuning.

butler ( 2018-08-02 16:37:24 +0300 )edit

Testing today on Xperia X Compact, and so far so good. I got a reboot one time as soon as I hit 'enter' to set 'fast' mode, but then I tried again after it booted and it was fine. I haven't looked much into the stats of the cpu to see exactly how much better or different the performance is, but everything seems smooth...

Levone1 ( 2018-08-03 22:59:19 +0300 )edit

After trying the first time, I rebooted, since I thought that the setting wouldn't change. And it felt much faster. ;-)

Maybe a little bit faster. But it's not a big boost.

wosrediinanatour ( 2018-08-05 14:14:03 +0300 )edit