Originally Posted by RichKnecht
A quick question. I know what LLC is and what it does. However, say I can run a particular OC at 1.22V and a LLC level of 6. Now, that same overclock can be achieved by raising VCore to 1.225 and lowering LLC to 5. From what I am seeing, the setting with higher vcore but lower LLC seems to run cooler in all benchmarks. Does this make sense, or am I imagining things?
THere's two ways to look at LLC on any voltage rail it is implemented on. The thing you are trying to control is call a Load Line Transient.
From a durability perspective, LLC is there to mitigate V_ovs. V_ovs is the inherent overshoot (milli sec) that occurs when you abruptly change the current flow on any voltage-clamped circuit (eg, VCCIN on x299). At stock settings the spec is somewhere around 50mV normal op, 200mV virus-mode (eg, heavy stability testing). The LLC-permitted droop creates a compensation window/margin for the overshoot that mitigates (most or some of) V_ovs ABOVE
what you set as the voltage in bios. So, when running these HEDT chips at an average overclock (what, +20%) you can expect occasional vccin excursions in the higher mV range, especially when doing things like 995 - tho new VRs control this much better than than before. It's a current-based effect, this is why you see more droop at high(er) current loads.
The other way to look at this is LLC also lets you compensate for the inherent undershoot (it's a oscillation around the set value) by starting at a higher voltage before vdroop... ever have a very cpu-intensive benchmark fail right when the bench ends? That's from undershoot. It's a balance.
Basically, IMO, for a 24/7 system, it is s good idea to allow for some "healthy" amount of droop of the rail LLC is acting on (VCCIN or vcore). Extreme benchmarking is different, and undershoot is the concern. In my experience (even in most benchmarks) I've never really experienced a scenario where it is better to meet voltage requirements with LLC increases (eg, lowering vdroop) than by simply increasing the voltage setting and allowing vdroop. In many implementations, LLC simply adds voltage to the value you set in bios... that's the wrong way to use LLC, IMO.
In the pics below, "vdroop" is labeled as "offset" in the early days. These are from socket 775 - when LLC settings were first made available in bios.