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CPU usage can't maintain 100% while stress testing (Core i7-3770K @4.5GHz with 1.250V)

5K views 67 replies 8 participants last post by  Nukemaster 
#1 ·
So I finally got a proper cooler to start overclocking, the overclock seems stable after 4 hours running Prime95, but I stopped there because I noticed that the cpu usage doesn't stay at 100%, and the frequency is all over the place.

The same thing happens with Prime95 and Intel Burn Test. For a while after starting the stress test it stays at 100%, but then it starts peaking, going down to about 45% and then back to 100% for a fraction of a second.

Here's a picture to better illustrate what I mean:


Temps are ok in my mind, maximum being 87 degrees with Intel burn test at maximum stress. Prime95 gets to about 80 degrees.

I have set the TDP and TDC in bios to 300W and 200A, so insufficient watts or amperage shouldn't be the issue.

I tried googling but found nothing. I tried intel burn test on my Windows tablet and there it stayed at 100% for the entire duration of the test (10 cycles), so I think it's not a part of the stress test.

What to do?

(Sorry if this is not the right section for this topic, couldn't find a more suited one.)
 
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#4 ·
Quote:
Originally Posted by deepor View Post

What does the graph in the task manager show if you switch it from the summary graph over into separate graphs for the CPU cores?
I ran intel burn test for a while and again it started dropping the usage. Here's a screenshot of that:

Quote:
Originally Posted by iinversion View Post

There are power settings for the VRM's in your bios. If they are not set properly they will throttle your CPU.

Screenshot your bios and tell us which mobo you have. Also make sure Windows power settings are on maximum.
I have a Gigabyte GA-Z77-HD3. Any specific part of the bios where you want a screenshot? I tried to find a VRM setting but couldn't find anything.

Edit: I have Windows power plan as best performance, if that's what you mean with Windows power settings.
 
#5 ·
It should be on the same main page where you change CPU ratio, voltage, etc. I have never used a Gigabyte board so can't tell you exactly.

That board has a very weak VRM setup though, it might be throttling despite what settings may or may not be set. It's a 4+1 phase and half of them aren't even heatsinked.
 
#7 ·
Yeah, looks like it just has those two VRM settings that you've already changed. I was wondering if there was others because I've seen up to 4 different settings on other boards.

It is likely that your VRM's are throttling because they are simply insufficient. It's a half-heatsinked 4+1 phase and 4.5GHz is probably making it throttle.

Try clocking it at say 4.2GHz @ 1.2v and see if the throttling still happens. If it doesn't, then you know it's because of the VRM's.
 
#8 ·
Quote:
Originally Posted by iinversion View Post

Yeah, looks like it just has those two VRM settings that you've already changed. I was wondering if there was others because I've seen up to 4 different settings on other boards.

It is likely that your VRM's are throttling because they are simply insufficient. It's a half-heatsinked 4+1 phase and 4.5GHz is probably making it throttle.

Try clocking it at say 4.2GHz @ 1.2v and see if the throttling still happens. If it doesn't, then you know it's because of the VRM's.
I can say that much that when I start the stress test and it stays at 100% temps are below 70 degrees. The moment it goes to 70-80 it starts dropping cpu usage. Will try that.
 
#11 ·
VRM stands for Voltage Regulator Module or something like that. If you look to the left and above of your CPU socket you will see some square things. Those square things are the chokes, directly to the left and above of them there are little black chips and those are the VRM's.

The ones to the left don't have any heatsinks but the ones above do. 4+1 phase VRM setup is very weak, especially without heatsinks and will be the main cause in limiting any OC for any chip AMD or Intel.
 
#12 ·
Quote:
Originally Posted by iinversion View Post

VRM stands for Voltage Regulator Module or something like that. If you look to the left and above of your CPU socket you will see some square things. Those square things are the chokes, directly to the left and above of them there are little black chips and those are the VRM's.

The ones to the left don't have any heatsinks but the ones above do. 4+1 phase VRM setup is very weak, especially without heatsinks and will be the main cause in limiting any OC for any chip AMD or Intel.
Alright, so my mb isn't an overclocking board
biggrin.gif
Intel burn test has been running for a while now and no drops in cpu usage so far. So I'm guessing it's the VRMs.

Will it damage anything if I use an overclock that causes that to happen?
 
#13 ·
No you won't damage anything as you can see your board is throttling the CPU to prevent the VRMs to fail. Some low quality boards don't even have that feature and will burn up and fail possibly taking components with them.

Personally I'd drop my OC to 4.4GHz and see if you can get a good voltage for that OC without throttling.
 
#16 ·
Quote:
Originally Posted by deepor View Post

The VRM settings in the BIOS are on a screen named "3D Power". Over there, you might have the temperature limit, but there's probably not really much to configure.
When I looked there I thought they were GPU related. I will send a screenshot of that page after I test how the 4.4GHz @ 1.22V works.
 
#20 ·
Quote:
Originally Posted by deepor View Post

Something else: check out the program "HWINFO". It might find interesting sensors on your board. On my GA-Z77X-D3H, it finds a sensor that shows power input and output and voltage and temperature readings from the VRM for the CPU.
Will look into it! Already installed it but it looks like it needs some closer attention.
 
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