Is it essential for Prime 95 Small FFT using AVX to assess the stability of a 9900k OC?
Is it essential for Prime 95 Small FFT using AVX to assess the stability of a 9900k OC?
LLC should remain at auto unless it doesn't cover the OC's needs; then mid mid-high (3 out of 5 or turbo, not extreme) is what you'll require most. Without it, the 9900k may experience boot issues, failing to load windows due to the CPU hitting a voltage that's too low. View: https://youtu.be/H5AM7yhvsPU
Man, that was really annoying. He dealt with it much better than I did.
I still don't understand how this connects to my own case. His setup wouldn't start when he changed the EVGA stock settings—something he never tried before because he went straight for an OC. It doesn't mention LLC, but it says the voltage was too low to boot. I'm fine with it now and can run most things except P95 with AVX.
Every guide I've read recommends setting LLC to 5/6 out of 8 on Asus boards. They warn that going too high can cause instability and might lead to undetectable voltage spikes that could harm your CPU.
Maybe I'll try again tomorrow.
The main idea I wanted to convey is that at stock configurations, J2c LLC was operating at auto mode, which meant his voltages weren’t sufficient to reliably start the CPU, though they would work afterward. By increasing the CPU’s overclock, he was able to manually adjust the LLC settings, ensuring stability. Your system behaves similarly in that scenario, where the VRM isn’t providing enough power when LLC is set to auto, causing the OC to fail at 4.9GHz.
Asus’ assessment holds true. A rating of 5 out of 8 falls in the medium to high range, making it suitable for most overclocking efforts. A 7 out of 8 is more suited for advanced users and world record attempts.
LLC adds extra voltage support. The CPU’s load fluctuates significantly, with spikes and drops. When the voltage drops too low—what we call vdroop—the CPU reacts immediately, and before the VRM can raise it, the CPU shuts down. That’s why LLC was introduced as a safeguard to handle those brief voltage drops, keeping the system stable.
As an applied voltage, LLC also influences peak performance. When the CPU needs high voltages from the VRM and gets them, LLC contributes further, causing the overall voltage to rise substantially. This means you only need to adjust enough to cover vdroop, not enough to overload the CPU or stress the VRM excessively.
You’d likely lower the Vcore slightly to around 1.2, add 5 LLC units, which pushes vdroop up to about 1.2 and brings the Vcore back nearer 1.3 while staying at 1.2v. This would result in a more stable performance swing of about 0.1v instead of the current 0.15–0.20v range.
Oh okay, thanks for the detailed response. I understand what you were getting at. My LLC is already set to 5 and I currently have a max swing of 0.155 - so maybe I should try for LLC6, although I have read a bunch of posts from people having problems with it,. Alternatively I suppose I could bump up the vcore to compensate for the droop.
Sorry if I was unclear. Still getting my head around all of this. Full settings
Vcore - 1.30v, 4.9GHz (all core), 0AVX Offset, Cache Ratio 45, LLC - 5, DRAM - 1.35v, VCCIO - 1.1v, VCCSA - 1.1v
Your measurements are quite accurate, but there are always adjustments and variations between CPUs and their performance.
Sure, I'm sure this wasn't a lucky draw. I'll keep refining it and watch how it goes. Appreciate all the tips! I'll look into that link.