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Prime95 uses low vcore?

post #1 of 5
Thread Starter 
I was stress testing with Prime95 and x264 and I noticed that they both end up using different max vcores. I'm currently using offset voltage I believe.

Prime95 uses 1.24v throughout my stress test, and x264 uses 1.264v. When I'm not stress testing and using my computer normally (things like steam and mozilla), it ends up at 1.312v.

I'm slightly confused as to why this happens, wouldn't a stress test want to top out your available voltage?

Here's where my concern lies, since Prime95 isn't using the maximum available voltage, wouldn't that mean if I increase the offset to prevent errors in Prime95, that when I use my computer normally it will have more vcore than it requires to be stable? Same thing with x264, since they both use less than 1.312v, which is what my vcore jumps to when I just use my computer normally.

I'm quite confused. Should I lower the vcore to the stable voltages in the stress tests so when I'm actually using my computer normally it will top out at a lower voltage?

Also I'm using an i5-6600k, currently clocked @ 4.4GHz, offset +190mV (which is what it needed to make prime stable). My motherboard is the ASRock Z170A-X1
Edited by Beanie - 8/27/16 at 1:19am
post #2 of 5
You are probably observing vdroop.

Most Intel platforms specify a degree of vdroop in order to protect the CPU from high transient voltages when entering and leaving high-loads. The more current the CPU draws (the higher the load), the more voltage droops.

This is normal and reducing VID (the voltage you set in the BIOS, which is the highest voltage a processor will spike to under the Intel specified load line), to the lowest voltage you see under load with vdroop intact will just result in overall lower voltages, which could well be unstable.

Most boards with any OC features will have a setting call load line calibration (or just vdroop), that lets you manipulate the amount of droop. If you find you need uncomfortably high idle voltages to remain stable at load (rare, because idle/low-load voltage really doesn't mean much as far as either power consumption or CPU wear) and you have a quality board, you can use an LLC setting that removes a significant portion of droop, narrowing the gap between light load and full load voltage. Removing too much vdroop is generally a bad idea, again because of the potential for extreme transients.
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post #3 of 5
Thread Starter 
Quote:
Originally Posted by Blameless View Post

You are probably observing vdroop.

Most Intel platforms specify a degree of vdroop in order to protect the CPU from high transient voltages when entering and leaving high-loads. The more current the CPU draws (the higher the load), the more voltage droops.

This is normal and reducing VID (the voltage you set in the BIOS, which is the highest voltage a processor will spike to under the Intel specified load line), to the lowest voltage you see under load with vdroop intact will just result in overall lower voltages, which could well be unstable.

Most boards with any OC features will have a setting call load line calibration (or just vdroop), that lets you manipulate the amount of droop. If you find you need uncomfortably high idle voltages to remain stable at load (rare, because idle/low-load voltage really doesn't mean much as far as either power consumption or CPU wear) and you have a quality board, you can use an LLC setting that removes a significant portion of droop, narrowing the gap between light load and full load voltage. Removing too much vdroop is generally a bad idea, again because of the potential for extreme transients.

I'm not quite sure what VID is to be honest. The only settings I've touched so far was the Multiplier and VCore settings. My motherboard doesn't have LLC as far as I know.

What should I do at this point? I don't like the idea of having my vcore set to 1.312v when under load from games or browsing, that feels too high for a 4.4GHz overclock, but I'm also concerned that if I lower it so that under load from usage would end up at 1.26v, that it would cause instability, since prime95 will fail with an error for sure since it will end up using less than 1.26v.
post #4 of 5
Quote:
Originally Posted by Beanie View Post

I'm not quite sure what VID is to be honest. The only settings I've touched so far was the Multiplier and VCore settings. My motherboard doesn't have LLC as far as I know.

What should I do at this point? I don't like the idea of having my vcore set to 1.312v when under load from games or browsing, that feels too high for a 4.4GHz overclock, but I'm also concerned that if I lower it so that under load from usage would end up at 1.26v, that it would cause instability, since prime95 will fail with an error for sure since it will end up using less than 1.26v.

Your system signature isn't loading for me. What CPU/motherboard are you using?

Anyway, you don't need to worry about light load voltage being too high. 1.26v while running Prime95 is vastly more stressful than 1.312v while playing a game or browsing the web, and reducing vcore for the lower loads isn't going to add much to the longevity of your part.
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post #5 of 5
Quote:
Originally Posted by Beanie View Post

My motherboard is the ASRock Z170A-X1

Pretty sure you have a load line calibration setting right under the voltage setting in your bios, i could be wrong though.

Blameless explained LLC pretty well, but here is also a good video which explains it with a graph: https://www.youtube.com/watch?v=Z8nFdFpuVBg

You should try to find a LLC setting (if your board supports LLC) that gives you the voltage you've set in the bios at idle, and some vdroop (~20mV) under load IMO.
VID (Voltage Identification Definition) is the reference voltage which is used to calculate VCore when you use offset voltage. VID+offset voltage=VCore
You can read out the VID with AIDA64 > Computer > Overclock > CPU VID.
You could also use a manual voltage first, to check how much the voltage u've set differs from the actual idle voltage and adjust your LLC that way first and change back to offset afterwards.

I don't know anything about the Z170 platform, but 72mV vdroop seems a little too much to me.
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