Re: [EXTERNAL] Re: linux-6.6.y regression on amd-pstate

[Mario Limonciello <mario.limonciello@amd.com>]

On 8/1/2025 2:14 AM, Jones, Morgan wrote:
> Hey all,
> 
> I think some form of this is back between 6.12 and 6.15 on our fractious AMD EPYC 7702. The symptom appears to be that the core will not boost past 2 GHz (the nominal frequency), so we lose out on 1.36 GHz of boost frequency. Downgrade from 6.15.7 to LTS (6.12.39) seems to fix it.
> 
> Keeping an eye out for other threads reporting similar symptoms on recent kernels:
> 
> [    0.000000] Linux version 6.15.7-xanmod1 (nixbld@localhost) (gcc (GCC) 14.2.1 20250322, GNU ld (GNU Binutils) 2.44) #1-NixOS SMP PREEMPT_DYNAMIC Tue Jan  1 00:00:00 UTC 1980
> 
> # cat /proc/cmdline
> [snip] amd_pstate=active amd_prefcore=enable amd_pstate.shared_mem=1
> 
> # cat /proc/cpuinfo
> [snip]
> processor       : 127
> vendor_id       : AuthenticAMD
> cpu family      : 23
> model           : 49
> model name      : AMD EPYC 7702 64-Core Processor
> stepping        : 0
> microcode       : 0x830107d
> cpu MHz         : 400.000
> cache size      : 512 KB
> physical id     : 0
> siblings        : 128
> core id         : 63
> cpu cores       : 64
> apicid          : 127
> initial apicid  : 127
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 16
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr rdpru wbnoinvd amd_ppin arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip rdpid overflow_recov succor smca sev sev_es
> bugs            : sysret_ss_attrs spectre_v1 spectre_v2 spec_store_bypass retbleed smt_rsb srso ibpb_no_ret
> bogomips        : 3992.75
> TLB size        : 3072 4K pages
> clflush size    : 64
> cache_alignment : 64
> address sizes   : 43 bits physical, 48 bits virtual
> power management: ts ttp tm hwpstate cpb eff_freq_ro [13] [14]
> 
> # cpupower frequency-info
> analyzing CPU 76:
>    driver: amd-pstate-epp
>    CPUs which run at the same hardware frequency: 76
>    CPUs which need to have their frequency coordinated by software: 76
>    energy performance preference: performance
>    hardware limits: 408 MHz - 3.36 GHz
>    available cpufreq governors: performance powersave
>    current policy: frequency should be within 1.51 GHz and 3.36 GHz.
>                    The governor "performance" may decide which speed to use
>                    within this range.
>    current CPU frequency: 1.98 GHz (asserted by call to kernel)
>    boost state support:
>      Supported: yes
>      Active: yes
>    amd-pstate limits:
>      Highest Performance: 255. Maximum Frequency: 3.36 GHz.
>      Nominal Performance: 152. Nominal Frequency: 2.00 GHz.
>      Lowest Non-linear Performance: 115. Lowest Non-linear Frequency: 1.51 GHz.
>      Lowest Performance: 31. Lowest Frequency: 400 MHz.
>      Preferred Core Support: 0. Preferred Core Ranking: 255.
> 
> Regards,
> Morgan
> 

Hello Morgan,

6.12 to 6.15 unfortunately includes a pretty big overhaul to the 
amd-pstate driver.  But I'm pretty surprised to hear this regression as 
we have had a lot of mileage on it across a very wide variety of hardware.

That being said:
1) Please capture a report using amd-pstate from amd-debug-tools 
(https://git.kernel.org/pub/scm/linux/kernel/git/superm1/amd-debug-tools.git/about/) 
both on a good and bad kernel and share them.

2) Can you reproduce on mainline 6.16?

If 1 and 2 don't lead an obvious answer:

3) Can you please bisect?

Thanks,