Xeon W-2245 is a new generation of high performance Xeons, the one with the highest clock rate essential for classic computation and simulation software (not the one with the highest power package). That was the main reason why I ordered particularly that CPU.
However, when starting a computation, the motherboard immediately issues Current/EDP limit throttling.
I think, it is not right, and probably the board was tuned for more power-hungry multicore CPU's. But the result is that the $13,000 priced system performs not better than a $3000 workstation-laptop.
The difficult part is that Dell has locked all the access to VRM/current limits tweaking, and I can not cut off this anchor with XTU or Throttlestop.
The new platform also have no "Intel(R) Dynamic Platform and Thermal Framework" engine driver, for disabling it, and unchaining the CPU.
So, did anyone find a Current/EDP limit solution for Cascade Lake CPUs on Dell motherboards? Is there any bios tweaking tool for these boards?
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Interesting. Seems, it is a new issue with Cascade lake Xeons, and it is NOT related to full load.
I tried overloading it with 200% of simulation work and these spikes disappeared.
Now, do you remember what "Voltage droop" is? It is a very stupid way of fighnting the reactive current spikes when core load drops rapidly. The older CPUs were requesting down-voltage at high loads, which was leading to system instability.
Now remember, that there are (roughly speaking) 3 types of throttle: 1)NOP cycles, 2)Clock down 3)protective full core halt
Number 2 and 3 should increase spikes. but carefully spreading NOPs in the conveyor can probably smooth down the spikes. But for that you have to analyze the conveyor load in advance, or guess the load from a voltage drop on a resistor in Vcc circuit of other cores/whole package.
Seems like Cascade Lake is able to issue such throttling NOPs.... But I wonder how it decides when to do that?
Now look at the graphs. All the spikes happen at low load when cores are ALREADY underclocked and underloaded.
So probablym that is a resistive sensor in VCC circuit, and it is either oversensitive, or senses some noise.
The latter means, the VCC circuit is badly designed.
In the best case, the sensitivity can be tweaked by developers in BIOS, and I hope, DELL will do something about that. Because unneeded throttle reduces performance in real-life applications.
I have a t5810 using a e5-1650v3. Playing around with it I run into the same throttles. The bios has a hidden intel rcsetup menu. I have an external programmer and all the bios modification tools. I have tried flashing my machine a dozen times with a modded bios to gain access to these options. Dell did a very good job at setting many defaults to make other settings not take affect. If and when I figure out how to modify the variables in the efi modules I will have full control over the current limits. I know you have a newer machine but the same would apply. If I figure this out I will post back and go through with you on how to pull a bios dump and I'll modify it for you. It's very upsetting to have such an expensive machine and not be able to use all the power. I modify voltage using throttle stop right now but if I don't change anything I get throttling at 25 percent load instantly with that 6 core...... I also have a massive cpu cooler I custom installed and made a vrm heatsink.
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Posted January 25th, 2021 13:00
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