為什麼 CPU 調速器不遵守最大 CPU 速度限制？

我跑了：

sudo parallel cpufreq-set -c {} -u 2000MHz ::: 0 1 2 3

然而，當我給 CPU 施加壓力時，cpufreq-info返回：

analyzing CPU 2:
 driver: intel_pstate
 CPUs which run at the same hardware frequency: 2
 CPUs which need to have their frequency coordinated by software: 2
 maximum transition latency: 4294.55 ms.
 hardware limits: 800 MHz - 2.90 GHz
 available cpufreq governors: performance, powersave
 current policy: frequency should be within 800 MHz and 2.00 GHz.
                 The governor "powersave" may decide which speed to use
                 within this range.
 current CPU frequency is 2.29 GHz.

2.29 GHz 高於 2.00 GHz。所有核心都可以看到這種行為。

就好像它完全忽略了頻率限制。

為什麼會這樣？有沒有辦法避免它發生？

$ uname -a
Linux travel 4.15.0-72-generic #81-Ubuntu SMP Tue Nov 26 12:20:02 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

$ cat /proc/cpuinfo
processor       : 3
vendor_id       : GenuineIntel
cpu family      : 6
model           : 42
model name      : Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz
stepping        : 7
microcode       : 0x2f
cpu MHz         : 1792.712
cache size      : 3072 KB
physical id     : 0
siblings        : 4
core id         : 1
cpu cores       : 2
apicid          : 3
initial apicid  : 3
fpu             : yes
fpu_exception   : yes
cpuid level     : 13
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm epb pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid xsaveopt dtherm ida arat pln pts md_clear flush_l1d
bugs            : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit
bogomips        : 4585.01
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

為了設置特定的頻率，cpufreq 中需要“使用者空間”調控器。

請參閱本文件中的“2.3 使用者空間”部分

引用自：https://unix.stackexchange.com/questions/561134