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Strange i7-2600K performance

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Noah977

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Oct 23, 2011
Hi,

This is my first overclocked machine.

Gigabyte P67A-UD4-B3
Intel i7-2600K
16GB RAM
Water cooled

It runs nice and cool with default bios setting. I have a fairly nasty math process that I run (Matlab.) It can run for days without a problem. The core temps are at 52

If I change the multiplier to 40, it will boot and run. But once I start a math intensive task (Matlab) It will reboot after 10-15 minutes. The temperature appears to be at 63-64 before the crash.

This seems odd, since Matlab is using one 1-2 threads at most, and the temperature is within a "reasonable" range.

My understanding was that I could just dial up the multiplier and things would work well as long as the value wasn't too extreme. The Vcore value is set to "auto". Clearly, I'm missing another critical step.

Note: I'm running Linux (Ubuntu), so the standard Windows diagnostic tools are not available to me.

Any suggestions on what I'm missing?
 
Try upping the vcore manually, try setting it to 1.25v. Auto doesn't always work that well. You may also need to increase the VCCIO voltage as well to help the IMC handle the 16GB of RAM.
 
Great. Will try that.

The RAM thing is interesting. prime 95 doesn't crash the box. But the matlab process does. The only difference I can see is that matlab uses around 3GB of RAM. Perhaps that is the issue?

What is a good setting for the VCCIO voltage, and where is it?

Thanks!!!
 
Try right around 1.1v, it generally works on auto, but that should be a safe value for you.
 
A couple of quick questions:

1) Is a multilier of 45 "reasonable" for a 24 hour machine running some critical processes, or is that pushing it too much?

2) What is a "reasonable" core temp to see as an upper limit before I should dial things back?

3) Are they any good tools for linux for diagnostics? (The Windows guys seem to have several.) All I really have is a temperature sensore

Thanks again!
 
4.5 should be just fine, you will just need to play with the vcore values. Try to keep it at or below 1.4v.

Regarding temps keeping it under 80C at 100% full load would be ideal.

Unfortunately not sure on linux diagnostics.
 
OS won't run with those setting :(

Boots to black screen of death...
 
4.0 with vcore of 1.25 and vccio on auto boots and runs beautifully.
4.5 with vcore of 1.25 and vccio of 1.1 fails
4.5 with vcore of 1.25 and vccio on auto fails
 
1.25 is too low for 4.5ghz, the 1.25 was just for the 4.0. For 4.5 try 1.35v.
 
OK. It boots but stress test crashes it. Then auto-reboot

Running a stress test in linux. Keeps all 8 virtual cores at 100% AND has 4 additional threads filling and clearing random chunks of 2GB sized memory. This crashed it in about 3 minutes :(
 
Try 4.4 then, if that fails try 4.3.
The difficulty is that every CPU is different, the settings that work nicely on mine may well not work at all on yours.
 
Interesting.

Another possibility is my OS.

Ubuntu has a "feature" of automatically frequency scaling the cpu. But, this is problematic as it trusts whatever the bios says is the max cpu speed. (Mine identifies as 4.0).

I can disable this in the bios, but turning off the os scaling feature and I assume that the bios will then just ignore instructions from the os.

Perhaps the OS gets upset when the cpu is running outside of the range it consideres possible?

Along those lines, Will the CPU run slower/cooler when my machine is idle? I'd hate to keep it cranking when nothing is going on.
 
I'm not sure how ubuntu handles it but with windows as long as you have c1e and eist (speedstep) turned on it will drop speed/voltage as needed.

I'm not familiar with how Linux/ubuntu handles overclocking but it is possible that it doesn't like more.

As bobnova pointed out try 41,42,43 etc to see if it is stable at those levels.
 
I've been running a really nasty stress test at 4.2 for the past two hours. Core temps around 70 and it seems solid.
 
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