Bug 217809

Summary: Core frequencies do not float correctly on AMD Ryzen 7 5700U when running on battery
Product: Power Management Reporter: Soren Stoutner (soren)
Component: cpufreqAssignee: linux-pm (linux-pm)
Status: RESOLVED CODE_FIX    
Severity: normal CC: carnil, soren
Priority: P3    
Hardware: AMD   
OS: Linux   
Kernel Version: Subsystem:
Regression: No Bisected commit-id:
Attachments: Screenshot of core frequencies

Description Soren Stoutner 2023-08-19 22:33:15 UTC 
On my laptop running an AMD Ryzen 7 5700U CPU, when on battery there are problems with the core frequency logic.  When a process consumes 100% CPU usage on a single core, the system forces the core frequency to the lowest value (399 MHz) instead of letting it float up to the highest frequency (4.3 GHz).  At the same time, other cores that have minimal CPU utilization will increase frequency up to the maximum, meaning that the CPU isn't locked to the lower frequency as a whole, but that something about
the frequency control logic isn't making the correct decisions.  This causes the system to run very slowly when on battery.

When the laptop is plugged in the behavior disappears, with cores that are consuming significant CPU able to increase the frequency to the maximum value.  Often after plugging in the laptop and then unplugging it, the correct behavior is maintained, although over time it usually reverts to the constrained behavior.  Also, sometimes this behavior will disappear if the laptop is suspended and resumed while on battery.  And, very rarely, the system boots up on battery and behaves correctly.  All of this indicates that there is some power management logic that is misbehaving in a way that was not anticipated.
Comment 1 Soren Stoutner 2023-08-19 22:38:15 UTC 
Created attachment 304913 [details]
Screenshot of core frequencies

This screenshot shows several KDE widgets.  The one on the top right shows core utilization, with the second core (blue) pushed to 100%.  The second widget down (which is expanded to the left with a detailed view) shows the frequency of each core, with the second core locked to the lowest possible value of 399 MHz.  It also shows that some of the other cores have floated up to higher values even though they have lower utilization.
Comment 2 Soren Stoutner 2024-01-27 22:32:12 UTC 
This bug was fixed in the 6.5.0 release.  Thank you.