My overclock i7 2700 at 4.5Ghz set at 1.38V from the bios shows as 1.392V from cpu Z when idling and 1.32V when under load. Just wondering if that's normal because I thought that under load voltage should be greater than idling voltage. Oh and LLC is set at level 4
That's called droop. As the processor pulls power the actual voltage will drop as it's eating up power. LLC helps eliminate that issue as it causes a spike when it first goes from no load to full load which the VRM's on the board react it sends a small spike of voltage to the CPU to compensate the surge of power consumption. That is one of the biggest issues with stability in overclocking. Some people have said at 1.4v that spike can jump from 1.2v to 1.6v if not more as the VRM's stabilize from the surge. The board will compensate and the droop will be the load voltage.
If I set my 2600k to a 1.2v fixed voltage, the full load would drop to about 1.17 or so completely and the spike would probably read around 1.21 or so in most applications as they aren't really capable of reading that quick spike that does happen when changing from idle to full load and back again.
Personally I've switched from fixed voltage to offset as it lets the CPU decide what voltage it really needs which has helped me find stability a lot easier. However, finding that perfect voltage to deal with heat and keep a 0.9v idle at 1600mhz was rather hard.
Your droop isn't as bad as you'd think. However I'd definitely watch the temperatures at that voltage on the sandy bridge as they seem to start getting warm at over 1.35v or so.
Thanks that's a really good explanation. My cooler is the h100i so far temperature is ok I think. Idle it hovers at 29-30 deg and at load it hovers between 59-61 deg. I feel like I can help bring down the temp a little more by tinkering with the voltage and LLC but if I try to bring down the voltage its not stable. You mentioned about an offset voltage however my motherboard bios doesn't have that setting and my motherboard is the gigabyte z68-UD3. Just wondering tho how far did you overclock you 2600K and what voltage did you set for it?
I actually run offset on my 2600k at 4.4Ghz of -0.040v and that's with zero LLC. I actually run stable high load at -0.050v but the idle down voltage drops too low and will actually cause instability when going from idle to load.
Now, LLC fights the vdroop as I said. My processor on my ASRock P67 Extreme 6 only drops a small margin when I'm at a fixed voltage. However, offsets have really eliminated any issue I've had with vdroop and haven't needed to boost my LLC from level 5 which has very little effect when compared to level 1. Remember, the higher strength the LLC is, the more wear and tear on your VRM as it has to push harder than it normally would to combat the vdroop.
Here's my freq to voltage table I have.. This is for fixed voltages so I have reference for setting up my offsets so I can keep speed step and low idle voltage.
3.4Ghz actually runs stable at 1.050v
4Ghz - 1.150v
4.2Ghz - 1.2v
4.4ghz - 1.225v
4.6ghz - 1.275v (not stress tested over time but posts and seems stable)
4.8Ghz - 1.35v (not stressed but will boot into Windows)
Now I hate fixed voltage, I don't want 1.2v rolling into my CPU while it's idling at 1600Mhz. If you click my CPU-Z Validation under my post you'll see my 4.4Ghz setup. It idles at 0.9v which is awesome and only on occasion does it go above 1.25v at full load.