Fixing AMD CPU Scaling on Fedora
Setting up the new AMD P-State Driver on Fedora with Kernel 6.4
Recently, after replacing my home server I noticed that the CPU (Ryzen 7600) was only scaling between 3000MHz and 3800MHz, which is the base and the first level boost clock of the CPU. I was expecting it to scale down to as low as 400Mhz when idle, and up to 5.17Ghz on boost.
Investigation
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: Cannot determine or is not supported.
hardware limits: 3.00 GHz - 5.17 GHz
available frequency steps: 3.80 GHz, 3.00 GHz
available cpufreq governors: conservative ondemand userspace powersave performance schedutil
current policy: frequency should be within 3.00 GHz and 3.80 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency: 3.00 GHz (asserted by call to hardware)
boost state support:
Supported: yes
Active: yes
Boost States: 0
Total States: 2
Pstate-P0: 3800MHz
Pstate-P1: 3000MHz
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
acpi-cpufreq
cat /sys/devices/system/cpu/cpu0/cpuinfo_min_freq
3000000
cat /sys/devices/system/cpu/cpu0/cpuinfo_max_freq
3800000
zenstates.py -l
P0 - Enabled - FID = 98 - DID = 8 - VID = C9 - Ratio = 38.00 - vCore = 0.29375
P1 - Enabled - FID = 78 - DID = 8 - VID = 79 - Ratio = 30.00 - vCore = 0.79375
P2 - Disabled
P3 - Disabled
P4 - Disabled
P5 - Disabled
P6 - Disabled
P7 - Disabled
C6 State - Package - Enabled
C6 State - Core - Enabled
After a significant amount of reading and hunting through BIOS settings only to find that ASRock have removed the CPPC enablement setting.
I found that while the new AMD P-State driver was merged into the kernel - it didn’t seem to load by default with kernel 6.3.11 which is the latest version in the Fedora 38 repositories.
Fedora is currently testing 6.4 and has test packages available, so I decided to give it a go - and it works perfectly.
Installing the new kernel
The kernel itself is stable, but it’s classed as a test package, so you’ll need to enable the testing repository.
dnf install koji -y
koji list-builds --package=kernel --after="2023-07-07" --pattern "kernel-6.4*"
mkdir -p kernel_test && cd kernel_test
koji download-build --arch=x86_64 kernel-6.4.2-201.fc38
dnf update kernel-*.rpm
Enable the driver
There’s one more step before rebooting, we need to enable the new AMD P-State driver.
- Edit
/etc/default/grub, addingamd_pstate=enableto theGRUB_CMDLINE_LINUXline. - Update the bootloader
grub2-mkconfig -o /boot/grub2/grub.cfg; dracut -f - Reboot
Check it’s working
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
amd-pstate-epp
cat /sys/devices/system/cpu/cpu0/cpuinfo_min_freq
400000
cat /sys/devices/system/cpu/cpu0/cpuinfo_max_freq
5170000
That’s the new pstate driver running and 400Mhz to 5.17Ghz!
And if we look at htop, we can see that individual CPU cores are scaling down to 400Mhz when idle:
0[ 0.0% 400MHz N/A ] 6[ 0.0% 400MHz N/A] Tasks: 193, 773 thr, 250 kthr; 1 running
1[ 0.0% 3672MHz 40°C] 7[ 0.0% 400MHz N/A] Systemd: running (0/739 failed) (0/411 jobs)
2[ 0.0% 400MHz N/A ] 8[| 0.7% 3592MHz N/A] Swp[ 0K/8.00G]
3[ 0.0% 400MHz N/A ] 9[| 0.7% 400MHz N/A] Load average: 0.49 0.30 0.20
4[ 0.0% 400MHz N/A ] 10[| 0.7% 3527MHz N/A] Disk IO: 0.0% read: 0KiB/s write: 0KiB/s
5[ 0.0% 400MHz N/A ] 11[|| 1.3% 400MHz N/A] Network: rx: 2KiB/s tx: 1KiB/s (12/5 pkts/s)
Mem[||||||||||||||| 2.73G/65G] Uptime: 00:16:32
There’s still something weird up with the hardware pstates which I suspect is something to do with the CPPC mode (action/passive etc…), but it doesn’t seem to matter as the frequency scaling is working as expected.
cpupower frequency-info
analyzing CPU 8:
driver: amd-pstate-epp
CPUs which run at the same hardware frequency: 8
CPUs which need to have their frequency coordinated by software: 8
maximum transition latency: Cannot determine or is not supported.
hardware limits: 400 MHz - 5.17 GHz
available cpufreq governors: performance powersave
current policy: frequency should be within 400 MHz and 5.17 GHz.
The governor "powersave" may decide which speed to use
within this range.
current CPU frequency: Unable to call hardware
current CPU frequency: 3.34 GHz (asserted by call to kernel)
boost state support:
Supported: yes
Active: yes
Boost States: 0
Total States: 2
Pstate-P0: 3800MHz
Pstate-P1: 3000MHz
I’m not sure if that’s a bug in the driver or the tool, but it doesn’t seem to matter 🤷.
Conclusion
Great success!
