While installing Gentoo on a laptop with an AMD A10-5750M APU using the Gentoo minimal-CD, I was troubled to see the CPU pegged at 3500MHz and consequent thermal cutouts shutting down the laptop. By reducing the number of jobs and using a desktop fan I managed to complete the installation.
When I rebooted into my own freshly compiled kernel I noticed the CPU
frequency would never go above 2500MHz. Investigating various files under /
sys/devices/system/cpu/cpufreq/policy* I was surprised to see there was
nothing I could do to either engage any of CPU's boost states, or to increase
the frequency above a maximum value of 2500MHz.
# cpupower frequency-info
analyzing CPU 0:
driver: acpi-cpufreq
CPUs which run at the same hardware frequency: 0
CPUs which need to have their frequency coordinated by software: 0
maximum transition latency: 4.0 us
hardware limits: 1.40 GHz - 2.50 GHz
available frequency steps: 2.50 GHz, 2.10 GHz, 1.80 GHz, 1.40 GHz
available cpufreq governors: ondemand userspace performance schedutil
current policy: frequency should be within 1.40 GHz and 2.50 GHz.
The governor "userspace" may decide which speed to use
within this range.
current CPU frequency: 2.50 GHz (asserted by call to hardware)
boost state support:
Supported: yes
Active: no
Boost States: 3
Total States: 8
Pstate-Pb0: 3500MHz (boost state)
Pstate-Pb1: 3200MHz (boost state)
Pstate-Pb2: 2800MHz (boost state)
Pstate-P0: 2500MHz
Pstate-P1: 2100MHz
Pstate-P2: 1800MHz
Pstate-P3: 1400MHz
Pstate-P4: 900MHz
For example:
# echo 3500000 | tee /sys/devices/system/cpu/cpufreq/policy3/scaling_setspeed
3500000
# cat /sys/devices/system/cpu/cpufreq/policy3/scaling_setspeed
2500000
Or, how about using cpupower?
# cpupower frequency-set -g userspace -d 900MHz -u 3500MHz
Setting cpu: 0
Setting cpu: 1
Setting cpu: 2
Setting cpu: 3
# cat /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed
2500000
Watching /proc/cpuinfo when compiling never shows the frequency reaching above
2500:
cpu MHz : 2495.389
cpu MHz : 2495.410
cpu MHz : 2495.389
cpu MHz : 2495.416
I can't think this is some hardcoded BIOS limitation, otherwise how come the
minimal-CD was boosting the frequency all the time to the point of shutting
down the laptop. Switching governor to 'performance' as the minimal-CD has it
set, or to userspace/schedutil has no effect to the maximum frequency the CPU
displays.
Any ideas how I can activate the boost states on this CPU, or what else I
could look into to unlock its potential and speed up my emerge?
--
Regards,
Mick
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