Software > Firmware
Messing with WOF Tables
cy384:
--- Quote from: ejfluhr on October 07, 2022, 01:19:54 pm ---Can you read out the processor frequencies and tell if it is boosting properly? Do you see ~160W when at idle? What about when running max threads off some heavy workload (e.g. Mersenne primes is a good one)?
--- End quote ---
I haven't looked closely at the frequencies, it idles around 30W and only approaches 160W under heavy load.
ejfluhr:
I copied that table CSV from GIT and filtered it to generate plots of frequency versus "CORE_CEFF" for a couple of different "VRATIO" values.
This link declares: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.54.905&rep=rep1&type=pdf
Power ~= VDD2 x Fclk x Ceff
where the effective switched capacitance, Ceff, is commonly expressed as the product of the physical capacitance CL, and the activity weighting factor α, each averaged over the N nodes.
I don't know how you can identify what "CORE_CEFF" is in your processor, but the equation shows how that correlates to power. I.e. smaller Ceff equals lower power.
Then the plot looks meaningful since the lowest frequency is at the highest CORE_CEFF and the frequency climbs as CORE_CEFF gets smaller, up to some limit.
Since the largest value of CORE_CEFF in the table is 1.0, that would be the highest power condition presumably associated with the 160W power rating of the table/processor.
I could not figure out how to post an image of the graphs, nor will the forum let me post the XLSX file with base data plus graphing tab, since it is too big. So I deleted a bunch of rows from the base data that had "NEST_CEFF" > 0.25. This let me shrink the XLSX file enough to post it.
The first tab is the CSV data as posted. The second tab "Plotme" is a filter + graph that can be manipulated by the red-colored cells; one variable showing a big difference is the VRATIO which can be modified by adjusting the VRATIO_INDEX box in integer values from 0 to 23 (the table has entries for all of those). The other 2 tabs are copies of the Plotme tab with just the values & graphs at VRATIO=1.0 and VRATIO=0.7498; this let me save and review them side-by-side. You could probably get fancy and plot all the variations on a single graph but I didn't care to go that far.
I picked VRATIO=1.0 and VRATIO=0.7948 because the maximum frequency changes substantially between all those values, starting at 3.4GHz and climbing to 3.8GHz. You can play with the VRATIO_INDEX in the Plotme tab and see how the frequency curve continues to increase at different CORE_CEFF values, though always capped to that 3.8GHz.
Raptor quotes the 190W 18-Core CPU as: 2.8GHz - 3.8GHz, so presumably you now have a 160W 16-Core CPU of 2.5GHz - 3.8GHz.
https://raptorcs.com/content/CP9M36/intro.html
CP9M36
IBM POWER9 v2 CPU (18-Core)
18 cores per package
2.8GHz base / 3.8GHz turbo (WoF)
190W TDP
User @deepblue was running an 18-Core CPU on a Blackbird mainboard, though with extra cooling:
https://forums.raptorcs.com/index.php/topic,99.0.html
Hopefully you will find out if, long term, the Blackbird can handle a 16-core P9 when it matches the TDP of the supported 8-core version.
Nice work! Please report back in a few months....
ClassicHasClass:
Just wanted to say, big fan of ssheven.
Nice work on getting it ramped up, though you've already found out that the vregs on the Blackbird could get marginal with high load. Basically you have the 8-core that Raptor sells but with the paired cores still on (the 8-core they sell, two of which are in this T2, is more or less the same 16-core you have there with the paired cores fused off). Like ejfluhr, I'll be interested to hear how it works out long term with the components; my Blackbird is a little 4-core.
ejfluhr:
>Basically you have the 8-core that Raptor sells but with the paired cores still on
What a neat observation! Something to consider is that 160W at 2.5GHz is probably achieved at much lower VDD than the 8c 160W at 3.45GHz (https://raptorcs.com/content/CP9M32/intro.html).
P=IxV => 160W = I_3.45 x V_3.45 = I_2.5 x V_2.5
If voltage moves 1:1 with frequency (I don't know if it does, could be 1:2 or 2:1, but got to start somewhere), then 3.45GHz/2.5GHz = 1.38x. So V_3.45 = V_2.5 x 1.38, alternatively V_2.5 = V_3.45 / 1.38.
So if P is constant, and V_2.5 is that much below V_3.45, then I_2.5 has to be increased by 1.38.
This is probably why the Blackbird wiki states: Other CPUs (CPUs with a TDP greater than 160W) may operate without WoF due to power regulator limitations.
Even without WOF (i.e. at the base of 2.5GHz), you are probably pushing those regulators much harder than the 8c module does.
I couldn't find any information on how much VDD current the Blackbird regulators can support. In the post by user deepblue, graphs indicate the processor was exceeding VDD load of 130A at 0.89v under some load. Doing stupid translation to 16c just to see where that lands is (130A / 18c) x 16c ~= 115, presumably lower as the 18c is 190W and the 16c is 160W. If your temps are running high, then perhaps the regs are only built to support ~100A and you are at or over that spec...
lepidotos:
I bought the same CPU and I'm looking at some of the other tables, I wonder if one of the ones for 140 W could be used instead, or the voltage dropped a little and the nest and base frequency dropped a lot. I guess I'll test undervolts when I get the chance, but if I do go too far and don't give the CPU enough power, is there a way to bump it back up to regular voltages?
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