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LLC confusion

post #1 of 4
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so ive been reading lots of posts about LLC, mostly people saying its bad for OC.
On my pc with LLC set on auto, the core voltage (according to everest and cpuz) stay at a constant 1.25v, meaning at idle it is at 1.25v and running prime it stays at 1.25v.
With LLC off, the core voltage is 1.23 idle and drops to 1.20 under load, which makes it unstable.
So, why is LLC bad? and why am i not seeing the "voltage spikes" everyone is freaking out about?
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post #2 of 4
You said why its bad in a way, it looks after Vdroop.

If your at 4.0 full load and the voltage drops the processor function correctly, and crash or bluescreen.

LLC will stablise that.
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post #3 of 4
I have run with it off and needed a higher Vcore setting in bios to stay stable. I now run with it enabled and have for many years on both rigs with no issues.
    
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post #4 of 4
Quote:
Originally Posted by PoNGxB View Post
so ive been reading lots of posts about LLC, mostly people saying its bad for OC.
On my pc with LLC set on auto, the core voltage (according to everest and cpuz) stay at a constant 1.25v, meaning at idle it is at 1.25v and running prime it stays at 1.25v.
With LLC off, the core voltage is 1.23 idle and drops to 1.20 under load, which makes it unstable.
So, why is LLC bad? and why am i not seeing the "voltage spikes" everyone is freaking out about?
You didn't need to make 2 threads man, just be patient for the responses if it falls to the 2nd page.

Anyway, I replied in your other thread, here is my response, but keep in mind as you read this (and I mention this in my quote) that LLC is rather unimpactful for you if you have similar idle & load voltages. In your case it is eliminating the vdroop which is causing you to be unstable. If you wanted you could just increase vcore so the vdroop was less significant, or you could just leave LLC on. Either way its not a big deal for you, because you have a FIXED voltage.

EDIT: While the case presented below is going from a low voltage to a higher voltage, the exact same effect occurs when going from a higher voltage to a lower one.

Quote:
Originally Posted by donkrx View Post
I mentioned this in a couple other threads - LLC will eliminate vdroop but it also does some behind the scenes work. Some have complained that higher LLC leads to voltage spiking, and this hints at the other function LLC has.

Even in a digital system, it is impossible to go from one voltage to another voltage instantly.... and if you don't get there in time, the system crashes. Something has to control the response and optimize its speed/behavior... typically this is done with PI/PID controllers (often just PI). LLC is the integral controller (the "I" in PID) which does 2 things: 1) helps eliminate some steady state error (in our situation, vdroop), and 2) increases the speed of the (voltage) response - at the expense of increased maximum overshoot and undershoot (spiking). Higher levels increases the effect in #1 and #2.

See the picture I attached, which keep in mind is HIGHLY exaggerated for our case. The blue line is our desired LOAD voltage which is held constant (if you are using Fixed voltage there won't be a big gap between your idle & load voltage, and this won't really apply). The black line shows you what "too much" LLC does. You get to the required voltage in time, but then immediately after undershoot it which would cause the system to crash. The red line shows how "not enough" LLC causes instability because of the slow response (NOTE: the vdroop here appears to be very small or not noticeable, that's just how the chart was created). In either of these unstable cases, you can obviously correct the problem with more vcore / load voltage. However, as you can see from the attached pic, you can also correct it by increasing/decreasing LLC, holding load voltage constant. This optimizes your voltage needs.

That being said, for Fixed/Manual voltage users, LLC really doesn't do much more than eliminate steady state error. If you are using Offset voltage and things like EIST, the gap can be significant, like 1.0v to 1.4v, so tweaking LLC is a good idea. However, it depends on YOUR cpu and YOUR settings.

Make sure you know which numbers mean more/less LLC on your mobo... in my UEFI/BIOS, it goes LLC 1,2,3,4,5 where LLC 1 is the highest. No clue what they were thinking, but whatever. For awhile I thought I was at the highest LLC setting, my brain couldn't accept that 1 was highest... lol.


Edited by donkrx - 8/16/11 at 3:50pm
    
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