On my new 7950x machine, I can set eco mode via Ryzen Master and this definitely has an effect and works like I would reasonably expect. Wattage is roughly 90w-110w while encoding, temps max out around 74c, which is fine.
But I've tried doing the same through the BIOS and it seems to make no difference at all. First I tried to set the machine to 105W eco mode via entering the PBO values as specified in this guide, under the "Advanced" -> "AMD Overclocking" section of the BIOS:
But this had no effect. When putting the system under stress, it runs as if it were on stock 170w power values, and I can see the temps go to 88c and the wattage go up to 220w during encoding. So I shrugged and went back to Ryzen Master eco mode.
Then I saw in the BIOS that there is another "Precision Boost Override" option under Extreme Tweaker in the BIOS, and *that* entry has an "AMD eco mode" option. So I set Ryzen Master back to default, then set that BIOS PBO option to "AMD Eco Mode"... and same result, which is no effect whatsoever in higher power levels. Runs as if set to 170w TDP, goes to 88c and up to 220w when encoding.
The only thing I can think of is that, during these tests, I set the Ryzen Master setting back to Default, so I didn't have *both* the BIOS and Ryzen Master setting set to Eco Mode. Is the Ryzen Master "default" setting somehow overriding the BIOS? If so, how do I resolve this? Should I just uninstall Ryzen Master completely if I want to handle this through the BIOS?
BIOS 0705 is at all defaults except for disabled wifi and bluetooth and q-codes set to show post codes only.
Okay, I answered most of my own questions, so I figured I'd share in case anyone comes up with the same questions I did.
First - I noticed in Ryzen Master documentation that it says if you update the BIOS you have to reinstall RM. I'm not sure if I initially installed RM first or updated to bios 0705, but either way, I didn't reinstall it after the bios update. And apparently uninstall/reinstall is considered part of routine maintenance. So I uninstalled it, and figured I'd test my questions out for myself.
This time, when I went into the Extreme Tweaker PBO setting, I noticed that it unlocks an additional "Eco Mode" setting that lets you set it to Auto, Eco 170w, Eco 105w and Eco 65w. Sweet! Since I didn't notice that setting before, it was left on Auto during the experiment I described in the OP, and may explain why I was still getting 170w. Or it might've still been RM overriding whatever I set in BIOS. Either way, point is, without RM installed, setting it to 105w Eco mode in BIOS worked. It runs hotter than what I got from RM Eco Mode so I am surmising that RM Eco does in fact set it to 65w. On the 105w setting, wattage seems to hover around 120w-130w with highest spikes to about 154w, which is about what I'd expect to see (I get that "65w" and "105w" are targets, not max limits).
Ran some tests. Encoding the movie The Godfather on my preferred h.265 Slow preset settings:
170w: 61 minutes 105w: 63 minutes 65w: 68 minutes
In the end I'll probably stick with 65w setting because it allows me to encode without getting fans revved up to full speed. And as RM seems to work to set it to that value without issue or needing a reboot, I'll probably use it going forward. If it would allow setting it to both 65w or 105w mode in Ryzen Master, that would prevent any real need to go into the BIOS for these settings, because from those test results, the performance difference between 105w and 170w settings is negligible. No point setting it to 170w ever. Being able to use RM to switch between 65w and 105w would therefore be ideal.