The reason why cpufreq sometimes can not reach that high speed...

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For example, on my lovely surface pro 3, I use acpi-cpufreq with ondemand governor,

it looks like when cpu is loaded with 100% for a while, the freq will drop below max freq,

say, the max available freq is 2.5G:

grep . /sys/devices/system/cpu/cpu3/cpufreq/scaling_available_frequencies2501000 2500000 2400000 2200000 2100000 1900000 1800000 1700000 1600000 1500000 1300000 1200000 1100000 1000000 800000 775000

however the actual freq is 1.9G:

grep . /sys/devices/system/cpu/cpu3/cpufreq/scaling_cur_freq1900000

This is because this platform is using RAPL for power limit, we can infer from

MSR IA32_THERM_STATUS = 0x19c bit 10~11:

10 Power Limitation Status (RO) 11 Power Limitation log (R/WC0)

rdmsr 0x19c                 88200c02

per surface pro 3 result, it is

rdmsr 0x19c                 88200c02

0xc means the bit 10~11 is set, so it means, thermal RAPL has take effect in controlling the freq

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