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EPYC Rome's infinity fabric clock speed

Question asked by ubarey on Jan 3, 2020

I'm considering to buy EPYC Rome(7002) platform.
I want to know how determined EPYC Rome's Infinity Fabric On-Package(IFOP) clock speed.

I only found this doc.
https://developer.amd.com/wp-content/resources/56745_0.80.pdf
"2.2.3 Memory Clock Speed" on the doc says:
> By default, the BIOS for EPYC 7002 Series processors will run at the maximum allowable clock frequency by the platform. This configuration results in the maximum memory bandwidth for the processor, but in some cases, it may not be the lowest latency. The Infinity Fabric will have a maximum speed of 1467 MHz (lower in some platforms), resulting in a single clock penalty to transfer data from the memory channels onto the Infinity Fabric to progress through the SoC. To achieve the lowest latency, you can set the memory frequency to be equal to the Infinity Fabric speed.


So There are questions.
1. Could IFOP clock speed be set to fixed clock speed by settings, or automatically be set by DDR4 RAM clock speed (like Ryzen)?
2. Maximum IFOP clock speed is 1467 MHz, so is DDR4-2933 best choice for latency rather than DDR4-3200? (I can't find any docs to recommend 2933 other than this doc.)
3. If I use DDR4-2666 RAM, what IFOP clock speed is maximum?
4. Does anyone have more detailed information about IFOP clocks on EPYC Rome?

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