Wrong CPU frequencies reported by cpu_get_tsc_freq() ?

[Nicolas Joly <njoly%pasteur.fr@localhost>]

Hi,

Just noticed that /proc/cpuinfo report wrong CPU frequencies in some
cases.

njoly@raya [~]> grep name /proc/cpuinfo | uniq
model name      : Intel(R) Core(TM) i7-3632QM CPU @ 2.20GHz
njoly@raya [~]> grep MHz /proc/cpuinfo
cpu MHz         : 2195.18
cpu MHz         : 4720.28
cpu MHz         : 2296.21
cpu MHz         : 2195.42
cpu MHz         : 2341.32
cpu MHz         : 2266.58
cpu MHz         : 3400.97
cpu MHz         : 2195.23

According to the Intel online documentation[1] for this specific
processor, frequency should be in the range 2.2GHz (base) - 3.2GHz
(turbo max).

But for some reason, cpu_get_tsc_freq() from sys/arch/x86/x86/cpu.c
report values outside the expected range.

Adding some debug print to display ci->ci_data.cpu_cc_freq value when
set, show the following :

njoly@raya [~]> dmesg | grep FREQ
cpu0: cpu_get_tsc_freq: FREQ 2195181560
cpu1: cpu_hatch: FREQ 2195181560
cpu2: cpu_hatch: FREQ 2195181560
cpu3: cpu_hatch: FREQ 2195181560
cpu4: cpu_hatch: FREQ 2195181560
cpu5: cpu_hatch: FREQ 2195181560
cpu6: cpu_hatch: FREQ 2195181560
cpu7: cpu_hatch: FREQ 2195181560
cpu2: cpu_get_tsc_freq: FREQ 2296213330
cpu3: cpu_get_tsc_freq: FREQ 2195418940
cpu4: cpu_get_tsc_freq: FREQ 2341319790
cpu5: cpu_get_tsc_freq: FREQ 2266578890
cpu6: cpu_get_tsc_freq: FREQ 3400965260
cpu1: cpu_get_tsc_freq: FREQ 4720276290
cpu7: cpu_get_tsc_freq: FREQ 2195227320

Any idea what's going on ?

Thanks.

[1] http://ark.intel.com/fr/products/71670/Intel-Core-i7-3632QM-Processor-6M-Cache-up-to-3_20-GHz-BGA

-- 
Nicolas Joly

Computing Group
Biology IT Center
Institut Pasteur, Paris.