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LLC? explain please!

post #1 of 4
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so ive been hearing a lot of people saying disable it if your overclocking, but i still dont understand it fully.
Can someone please explain to me what it does and how it will effect voltage in my PC?
i have a i7 920 at 3.67 Ghz, at 1.25v in windows and in bios its 1.268v with LLC set at auto.
The settings in bios for LLC are auto, standard, level 1 and level 2.
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post #2 of 4
LLC = Load line calibration, it helps compensate the vdroop, vdroop is when the voltage is lower than what is set in the bios when it is under load. Different levels or settings of LLC can help with that.
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post #3 of 4
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.

edit: removed some stuff that was not relevant.

Edited by donkrx - 8/16/11 at 3:38pm
    
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post #4 of 4
Excellent, full blown description! Very nice donkrx!
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