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akiroz

Member

Registered: 2015-02-28

Posts: 8

Different clock frequency on hyper-threaded cores?

I'm not sure if this is the right place to ask, It's not really an issue but has be bothering me for some time now and google didn't find an answer for me....

I'm currently using an i7-5500U with 2 physical cores (4 HT cores).
Yet, when I check the clock frequency on the system it shows a different value for each of the 4 HT cores:

cat /proc/cpuinfo | grep MHz
cpu MHz		: 3001.031
cpu MHz		: 2975.906
cpu MHz		: 2994.468
cpu MHz		: 2901.562

How can this be possible when there are only 2 physical cores?
Shouldn't the HT cores share the same frequency on the same physical core?

If I'm getting this right, hyper-threading simply means interleaving 2 instruction streams into a single (physical) core to reduce pipeline hazards right?

This just boggles my mind....

Last edited by akiroz (2015-06-06 19:05:33)

ashleygc

Member

From: Europe

Registered: 2014-06-23

Posts: 12

Website

Re: Different clock frequency on hyper-threaded cores?

Do the numbers ever swap order? Are the numbers fixed or do they change over time?

akiroz

Member

Registered: 2015-02-28

Posts: 8

Re: Different clock frequency on hyper-threaded cores?

The numbers are different each time, here are 3 more samples:

cat /proc/cpuinfo | grep MHz
cpu MHz		: 2937.187
cpu MHz		: 2954.250
cpu MHz		: 2977.500
cpu MHz		: 2990.250

cat /proc/cpuinfo | grep MHz
cpu MHz		: 2954.812
cpu MHz		: 2981.812
cpu MHz		: 2996.343
cpu MHz		: 2987.062

cat /proc/cpuinfo | grep MHz
cpu MHz		: 2969.250
cpu MHz		: 2936.718
cpu MHz		: 2985.093
cpu MHz		: 2980.031

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,893

Re: Different clock frequency on hyper-threaded cores?

In many cases, a core with hyperthreading has some parts of the core physically duplicated .
This puts a hyperthreaded core somewhere between a single core and  a dual core system.

Your processor cores may have enough parts duplicated to allow different clock speeds.
If you search, you might be able to find block diagrams for your processor that clarify which parts are duplicated physically in the cores.

---

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Try clean chroot manager by graysky

akiroz

Member

Registered: 2015-02-28

Posts: 8

Re: Different clock frequency on hyper-threaded cores?

Ahh thanks, that makes a lot more sense now!