Question Disable Ryzen 3600X PBO for Undervolting?

Boris_yo

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Feb 14, 2010
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Hi,

First, a question I had:

The difference between Precision Boost (PB) and Precision Boost Overdrive (PBO) is when former boosts CPU clock to it's maximum based on die's temperature while the latter boosts CPUs maximum clock even further by "overdriving" it but now it's based on CPU voltage?

For example: after CPU has reached it's 4.2GHz clock speed with PB and still has thermal headroom to boost higher, it tells PBO that and then PBO checks for current voltage. If voltage is safe it applies more voltage, therefore overdriving 4.2GHz clock speed and pushing it higher?

Is it how PB and PBO work?

Now about my question about undervolting and PBO. I want to undervolt CPU without overclocking it. I want to reduce voltage to as low as CPU allows while operating in it's stock clock speed.

Since I will be locking down voltage value, must I disable PBO? Or even when enabled, PBO won't work because it won't be able to control voltage that is locked?

Should I do undervolting in BIOS or Ryzen Master utility? Is Ryzen Master utility safer because the modifications made will only work while utility is running in Windows 10?

Thanks.

System specs:

CPU: AMD Ryzen 5 3600X (stock cooler)
Motherboard: Gigabyte B450 Aorus Elite (rev 1.0)
RAM: 2x8GB Corsair Vengeance LPX 3200MHz
GPU: EVGA GeForce RTX 2060
SSD: Samsung EVO 970 Plus 250GB
HDD: Western Digital Blue 2TB
 
Hi,

First, a question I had:

The difference between Precision Boost (PB) and Precision Boost Overdrive (PBO) is when former boosts CPU clock to it's maximum based on die's temperature while the latter boosts CPUs maximum clock even further by "overdriving" it but now it's based on CPU voltage?

For example: after CPU has reached it's 4.2GHz clock speed with PB and still has thermal headroom to boost higher, it tells PBO that and then PBO checks for current voltage. If voltage is safe it applies more voltage, therefore overdriving 4.2GHz clock speed and pushing it higher?

Is it how PB and PBO work?

Now about my question about undervolting and PBO. I want to undervolt CPU without overclocking it. I want to reduce voltage to as low as CPU allows while operating in it's stock clock speed.

Since I will be locking down voltage value, must I disable PBO? Or even when enabled, PBO won't work because it won't be able to control voltage that is locked?

Should I do undervolting in BIOS or Ryzen Master utility? Is Ryzen Master utility safer because the modifications made will only work while utility is running in Windows 10?

Thanks.

System specs:

CPU: AMD Ryzen 5 3600X (stock cooler)
Motherboard: Gigabyte B450 Aorus Elite (rev 1.0)
RAM: 2x8GB Corsair Vengeance LPX 3200MHz
GPU: EVGA GeForce RTX 2060
SSD: Samsung EVO 970 Plus 250GB
HDD: Western Digital Blue 2TB
I suggest you try this first: https://www.guru3d.com/articles-pages/clocktuner-for-ryzen-ctr-guide-download,1.html
It does that job for you with no sweat.
 

hotaru.hino

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Sep 1, 2020
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Since I will be locking down voltage value, must I disable PBO? Or even when enabled, PBO won't work because it won't be able to control voltage that is locked?
Setting a fixed voltage will not disable dynamic frequency scaling. However, you should set a fixed multiplier to disable dynamic frequency scaling because the CPU will still try to boost to its fullest, which will cause the processor the crash.

Should I do undervolting in BIOS or Ryzen Master utility? Is Ryzen Master utility safer because the modifications made will only work while utility is running in Windows 10?
You should do it in the BIOS since the settings will be applied from boot. You can start with the Ryzen Master to figure out when the system becomes unstable, but the settings should be put in BIOS afterwards.

EDIT: Alternatively if power saving/thermal management was your goal, you can instead lower the PPT limit. While this greatly impacts all core boosting if there's something to do on all cores, the processor can usually retain full boost on at least 2 cores loaded. This is much simpler to do than setting a fixed voltage and finding the multiplier combination that works.
 
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Hi,

First, a question I had:

The difference between Precision Boost (PB) and Precision Boost Overdrive (PBO) is when former boosts CPU clock to it's maximum based on die's temperature while the latter boosts CPUs maximum clock even further by "overdriving" it but now it's based on CPU voltage?

For example: after CPU has reached it's 4.2GHz clock speed with PB and still has thermal headroom to boost higher, it tells PBO that and then PBO checks for current voltage. If voltage is safe it applies more voltage, therefore overdriving 4.2GHz clock speed and pushing it higher?

Is it how PB and PBO work?
...
Not exactly, but pretty close.

Precision Boost will boost one core from it's (as low as) base clock up to a maximum clock when it sees enough thermal headroom to the limits established for the processor. It will boost all cores to a lesser clock that's based on the thermal margin and available power margin to the processor limits. The power margin is the PPT, and core currents: TDC and EDC (total core current and peak core current)

It raises the voltage to keep the processor stable at the high boost frequency because it very quickly draws a lot more current and just as quickly draws a lot less when the boost goes away. That sudden change in current makes voltage output by a VRM unstable (it's called undershoot and overshoot). Since unstable voltage makes a processor unstable, a high voltage means even if it (voltage) is unstable at least it's enough to keep the processor stable. It does it very briefly and only when temperature is low enough to be safe.

It also lowers how high it will raise the voltage...and therefore how high it can boost the clock...based on the temperature of the cores also to keep it safe. It's also watching the core current and power draw (TDC. EDC and PPT) and limiting boosting as it reaches those limits.

That's Precision Boost at work, at least as I understand it.

What PBO does is it says to the processor: ignore (or raise) the power limits established for the processor. Boost even if the power limits are being exceeded (PPT, TDC and EDC). If it's no longer keeping below the established power limits it will keep all-cores boosted to higher clocks longer, up until thermal limits are making it pull back on clocks. That's why better cooling is essential for PBO to work best: it's still looking at thermal limits to keep the processor safe.

PBO doesn't do much for max clock boosting with Zen2. Even though some report getting more than the specc'd clocks sometimes, light threaded BM scores don't increase much at all. What it really does is help it attain and hold higher mid-range clocks while working hard, and therefore multi-threaded BM's can increase substantially with better cooling. Again, that's when better cooling helps even more as it is mostly by core temperature that limits how long it will hold the clocks high for mid-range boosting.

I think PBO get's a reputation as inneffective on Zen2 (it was much more effective on Zen1.5) because people don't take the time to run some meaningful benchmarks or run it on stock Wraithe coolers. It definitely puts out a lot more heat, and so is a lot less efficient, but when cooled right it does increase performance too.
 
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EDIT: Alternatively if power saving/thermal management was your goal, you can instead lower the PPT limit. While this greatly impacts all core boosting if there's something to do on all cores, the processor can usually retain full boost on at least 2 cores loaded. This is much simpler to do than setting a fixed voltage and finding the multiplier combination that works.
I disagree totally, that's a bad idea for the reason you mentioned: it will limit all-core boosting even when not heavily loaded. Also, there are much better options available.

Firstly: Zen2 already has a terrific power manager built-in that operates fast and efficiently: that's Precision Boost, the boosting algorithm. All you have to do is set the system up right and it works great. The real problem comes from paying too much attention to the temp spikes that occur when boosting as they aren't thermally significant. Pay attention instead to the AVERAGE temperature readouts in HWInfo and RyzenMaster. Take the time to understand what's happening and you'll see it's better to JUST RUN STOCK than gaming it with misguided tweaks.

Second, if wanting to limit thermals use the Platform Thermal Limit setting. Just set it to the limit and it will ONLY limit boosting when it's exceeds the AVERAGE temperature limit you set it at. Below that limit it will freely boost as needed and maintain performance levels, just don't set the limit too low. I use an 85C setting for my system and it's perfect.
 
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