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Firmware / Re: Messing with WOF Tables
« Last post by bobpaul on March 17, 2025, 07:51:37 pm »>That link doesn't seem to work, do you happen to still know how to navigate to it or know the name of the paper.
Sorry, I don't. As I recall, it was an educational presentation/paper on how processor power is modeled. It is pretty well known material, maybe you can find other references.
hmm, ok. I thought it might be more specific to these processors.
It's been a long time, but I believe VRATIO just means the number of ON cores (a.k.a. active) relative to the maximum available. As the # of active cores goes down, the power from those cores is applied to the remaining cores, allowing them to boost to higher frequencies. Depending on the system & power limit, the proc could pretty quickly apply so much power credit from offline cores that it flat-lines at the maximum possible frequency, i.e. it becomes technology limited not power limited. It sounds like, for that table, the processor is only power-limited when >= 12 cores ON. Technically VRATIO is "voltage ratio" intended to handle quads using the internal voltage regulator at some % below the input voltage, but it ended up not getting supported and devolved to tracking # of cores. A core in a stopped state with the power headers off has voltage of 0v hance VRATIO=0 for that core, and you add up the # of ON vs OFF cores to get he VRATIO.
Ah-ha. So that's why VRATIO_INDEX is always 0-23 and VRATIO_STEP is always exactly 1/24 to 3 figures. VRATIO_STEP is always 0.0409 to account for rounding in VRATIO_STEP to ensure that 23*VRATIO_STEP + VRATIO_START == 1. So really, VRATIO_INDEX is the easier to follow number since it's just the number of active cores. And for a 16 core CPU, one should be able to ignore any VRATIO_INDEX > 15, as 0-15 cover 1-16 active cores, right?
I don't believe Linux ever implemented support for different quad frequencies so they all just run at the same frequency? If true, WOF only uses FRATIO=1.0 indices.
Certainly in Linux I see different frequencies on a per-core basis, but I understood that to be simply what the kernel was requesting rather than what it's actually running at. I had thought it was the case where if 2 active cores in a quad had requested frequencies of 2200 and 1800 then the quad (and thus both cores) would run at 2200MHz. Linux knows that 4 threads are the same core, so those always show the same frequency, but I understood Linux didn't actually know about the quads and rather I thought it was the PNOR that was really in control of the quad frequencies. But I don't know of any way of checking what frequency a core (or quad) is actually running at.
All of the tables have FRATIO_STEP of 0.1, FRATIO_START of 1, and FRATIO of 0.6, 0.7, 0.8, 0.9, or 1.0. But... yeah, holding vratio constant and looking at fratio, it does not look like the fratio value has an impact, at least for this csv:
For reference, CORE_CEFF is the ratio of the workload switching power relative to TDP, where TDP=1.0. So 0.5 means the workload has half the switching power of TDP. If the workload is using less power, the WOF table should attempt to raise frequency, up to the maximum allowed, where it flatlines. Similarly, if there are fewer cores active, the frequency will go up, and if both are true, the frequency will go up more. So that explains the shape of that plot.
OK, I don't understand the name, but that makes more sense than my assumption that it was a physical property related to the switching capacitance.
