Intel turbo boost not working, why?

[jbendsen]

Hi there and good day to all :-)

I have an intel server board s2400sc2 with two E5-2450 xeon cpu's, with vsphere 5.1.

When the cpu load is 100% on all 32 cores, on windows 7 ultimate 64 bit, the core speed is only 2.1 GHz, I would expect it to go up to 2.9 GHz, any ideas on where to configure?

Thanks

Jesper

[schepp]

Hi,

with all 8 Cores on 100% per CPU I would expect 2.6 GHz, as the E5-2450 is labed with a Turbo rate of 5/5/6/6/7/7/8/8. This means 2.9 GHz is only possible with one or two active cores. (when the other limits such as temperature and power consumption are ok)

I would take a look in the BIOS if you forgot to enable any feature. Sometimes it's just labeled as a "performance mode".

Regards

[jbendsen]

hmm, spec says normal is 2.1 GHz and max is 2.9 GHz. So basically you say I have bought a car where the specs say it can go 250 km/h, meaning first wheel can go 100 km/h, second wheel 150 km/h, third wheel 200 km/h and fourth wheel 250 km/h? If so this is hilarious and Intel will get the two cpu's back for a refund hahahahahah

[schepp]

Well you did buy a CPU and no car :smileywink:

That's just the way Intel Turbo Technology works. You have a multiplier of 5/5/6/6/7/7/8/8 depending on active cores and multiply that with the specific overclock frequenz of the CPU, which is 100 MHz in your case. When you fire up all 8 physical cores it's just not possible to overclock all cores to full speed without getting into problems with the power consumption, and heat production. For the max speed of 2.9 GHz the CPU needs to disable 6 cores to. I think 500 MHz overclock on all 8 cores is pretty good.

I don't see why this should be hilarious. It's mainly physics and common sense.

If you need a higher clock rate, buy a CPU with a higher base clock rate.

Regards

[jbendsen]

I guess it is all about expectations, and my expectations was that all 16 vCPU would go up to 2.9 GHz. But anyway how do I verify that vsphere actual uses turbo boost, I wont believe until I see it somewhere...

Thanks for the elaboration :-) I should buy a new car...

[schepp]

:smileywink:

the vSphere Client might show a CPU utilization above 100% and For the i-Series there is the Intel Turbo Boost Technology Monitor which can be found here: https://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=19105

Don't know if it works with Xeons though.

Regards

[jbendsen]

Thanks, tried already does not work with xeon, and by the way for i3, i5, and i7 all cores uses the same turbo boost speed, so I find less and less reason to use xeon. Where did you find info that not all cores on exon uses same turbo boost speed?

[schepp]

The i-CPUs work the same way. If all the cores get boosted the maximum clock rate will be lower as if only one core gets boosted.

[jbendsen]

you are wrong, see this...

Is turbo frequency the same for all active cores in the processor?

Yes.

This applies to:

Intel® Core™ i5 Desktop Processor Intel® Core™ i7 Desktop Processor Intel® Core™ i7 Processor Extreme Edition

Above info found here:

http://www.intel.com/support/processors/sb/CS-029908.htm

Anyways, can anyone else verify that turbo boost on a xeon is not the same on all cores?

And how do you verify that turbo boost is on?

Thanks :-)

[jbendsen]

Is this some kind of proof?

It seems like 2 cores are working harder than all the rest cores, even thought all is 100% in task manager, someone please tell me if I am reading this right?

[jbendsen]

YEEEEESSS here we go...

Here you can see that all 32 vCPU (16 cores) are at the speed of 2.9 GHz.. hahahaha I am happy :-)

[schepp]

No I'm not.

As the Intel site says:

It is the same frequency for all active cores.

But the height of the frequency is depending on the number of active cores. And this is valid for i-Series and Xeons.

I never said Xeons run on different frequencies per core. All active cores will run the same speed. But if you want to achieve the 2.9 GHz only 2 cores can be active. The other 6 need to be in at least C3 state.

If all 8 cores of your xeons are active, all the cores can run on max 2.6 GHz.

As I said in my first post, you need to enable the Intel Turbo Boost in BIOS. And for testing I would only bring 2-4 cores to 100% and watch the CPU utilization in vSphere Client if it goes beyond 100%.

Regards

[jbendsen]

OK, I just want to understand so help me, the screen dump form vsphere shows that 32 vCPU's are running 3.1 GHz. I am happy about that, this is much higher than the 2.6 GHz you state, and even higher that the 2.9 GHz that Intel states. Help me here...

[schepp]

I can't really tell you what we are seeing here. All I can tell is, that this is not the way Turbo Boost works :smileywink:  For example here is a Turbo Boost frequency table for Core i7: http://www.intel.com/support/processors/corei7/sb/CS-032279.htm

It shows you "Bin Upside" for each number of active cores. Max Turbo Boost frequency is then = "Bin Upside" x 100 MHz + base clock rate

Maybe vSphere is confused by all this turbo boosting, hyper threading stuff :smileywink:

What does your CPU-Z say?

[jbendsen]

Hi again

Yes, cpu-z says 2.1 GHz no matter what, and vsphere says 3.1 GHz when cpu is 100%. I agree that the highest speed can be 2.6 GHz accordingly to Intel. So we have a bug here, somewhere.....

Thanks for your help.

/Jesper