PBO and Curve optimiser on AM5 - voltage usage seems like it could be improved

[g67575]

I was just wondering why the voltage usage isn't lower when PBO is tuned / untuned on Ryzen 7000 CPUs.

It seems like in a lot of cases, the voltage can be set lower if configured manually, without issues.

For example, running CPUz, the average CPU voltage is 1.25v with PBO configured (Frequency is roughly 5.2Ghz), and my CPU hits the thermal limit I defined - 90 degrees with air cooling.

If I manually set the voltage to run at 1.20v, and the frequency to 5.2Ghz, the CPU seems to run happily and runs nearly 10 Celsius cooler, and doesn't hit the thermal limit.

ASRock has a handy utility that lets you easily switch between PBO and manual overclocking on the fly (Blazing OC Tuner).

So, couldn't AMD optimize PBO to reduce voltage under full load? Couldn't the PBO algorithm be improved, especially under lighter workloads like CPUz and for gaming?

Voltage seems to be the main limiting factor on the Ryzen 7000 series CPUs, in terms of reaching higher frequencies.

 

[jigger]

Not all chips are the same, but this is more a decision for motherboard manufacturers.

 

[alec]

average CPU voltage is 1.25v with PBO configured

Its unclear if you have also tuned curve optimizer or just tweaked PBO power limits.
CO is the place that would reduce voltage for a given frequency

 

[g67575]

I have PBO enabled with a negative curve set to -15 (all cores), which is stable. I found that disabling c-states improved stability when reducing the voltage via the curve optimiser setting.

Reducing CO seems to be less effective than a straight forward manual OC, at least at 1.2v. The main problem with that is the thermal limits don't work when a manual OC is used, so not great for benchmarks like P95, which uses much more power than pretty much anything else.

Higher voltages affect these chips to a large extent, I think they need to do more optimization to keep the voltages low. Presumably if it's possible to manually OC and run voltage at 1.2v or maybe lower, a similar result should be possible with PBO.

It could be that they are keeping the voltages a little higher with PBO enabled, to allow individual cores to quickly boost to higher frequencies, like 5.5-5.7Ghz and remain stable.

 

[alec]

It could be that they are keeping the voltages a little higher with PBO enabled, to allow individual cores to quickly boost to higher frequencies, like 5.5-5.7Ghz and remain stable.

that is sort of it. Curve tuning happens across the whole curve, including the top clocks. It may be that voltage point for 5.2GHz can't go as low as 1.2V because then the 5.7GHz becomes unstable for example.

You could reduce the clock ceiling, then tune CO more and achieve higher all core efficiency
[In Gigabyte bios] PBO section, Max CPU Boost Clock override can go negative to 200.

 

[g67575]

that is sort of it. Curve tuning happens across the whole curve, including the top clocks. It may be that voltage point for 5.2GHz can't go as low as 1.2V because then the 5.7GHz becomes unstable for example.

You could reduce the clock ceiling, then tune CO more and achieve higher all core efficiency
[In Gigabyte bios] PBO section, Max CPU Boost Clock override can go negative to 200.

Might work, say with a 85/80 Celsius temp limit.

I think my ASRock Bios allows 400/500 reduction in max frequency. I tried it at -350 yesterday (limits to 5.2Ghz), but didn't change the curve optimiser setting from -15.