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andreas-h
Asked: 2013-02-01 02:50:53 +0800 CST

Why does /proc/cpuinfo show contradicting processor speeds?

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On a system running Gentoo Linux (3.1.6, x86_64), I have two six-core Intel Xeon CPUs (X5675).

cat /proc/cpuinfo correctly shows me 12 processors. However, I don't understand why the processor speed in the model name line differs from the cpu MHz number:

processor   : 11
vendor_id   : GenuineIntel
cpu family  : 6
model       : 44
model name  : Intel(R) Xeon(R) CPU           X5675  @ 3.07GHz
stepping    : 2
cpu MHz     : 1600.000
cache size  : 12288 KB
physical id : 1
siblings    : 6
core id     : 10
cpu cores   : 6
apicid      : 52
initial apicid  : 52
fpu     : yes
fpu_exception   : yes
cpuid level : 11
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 pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 sse4_2 popcnt lahf_lm ida arat epb dts tpr_shadow vnmi flexpriority ept vpid
bogomips    : 6133.17
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

EDIT: htop shows all processors at 100%, and the load average is 24.66 24.33 24.67. So it seems none of the processors are idling. However, a watch -n5 "cat /proc/cpuinfo | grep MHz" shows that the first six cores are constantly at 3067MHz, while cores 7-12 are always at 1600MHz. I'm puzzled. I'm not sysadmin of these machines, but before I start bugging our sysadmins about this, I wanted to be sure that this is not the behaviour which is to be expected. Is there any way to find out if SpeedStep is enabled without going into the BIOS, i.e. with non-root-priviledges?

EDIT2: as requested, I posted a full output of /proc/cpuinfo here: https://gist.github.com/4683911

linux

5 Answers

  1. The processor speed in the model name line is part of the processor's model name. The processor's actual name is "Intel(R) Xeon(R) CPU     X5675 @ 3.07GHz".

    The processor speed in the "cpu MHz" line is the current CPU clock speed.

    Presumably, the CPU is not very busy now and is running at a reduced speed to save energy and keep cool. If you overclocked the CPU, the speed in the "cpu MHz" line could be higher than the speed in the model name. If you gave the system some work to do, they'd probably be equal.

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  2. Your processor is called Intel(R) Xeon(R) CPU X5675 @ 3.07GHz and contains a tech called Intel SpeedStep.

    Speedstep lowers the clock frequency of the CPU when the CPU has no work to do. This is mainly a power saving feature, and can normally be switched off in the bios.

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  3. In BIOS change Power Management Profile from "Power saver" to "Performance"

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  4. One way of getting detailed Processor information without rebooting your machine is to use dmidecode

     dmidecode --type Processor
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  5. It might also be possible that there are external forces at work. Specifically something like Intel Node Manager which will adjust the power consumption of a host by adjusting processor P-states.

    To check if this is active see /proc/acpi/processor/*/info. See also http://acpi.sourceforge.net/documentation/processor.html

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