Adjusting IIO_LLC_WAYS for Increased DDIO Portion on Intel Xeon Gold 6354

[sc3289]

Hello.

I am currently working with an Intel Xeon Gold 6354 processor and attempting to increase the DDIO portion of the LLC (Last-Level Cache) through MSR settings.

Specifically, I have been using the wrmsr 0xc8b command to modify the IIO_LLC_WAYS setting, aiming to allocate a larger portion of the LLC to DDIO. However, upon testing with iperf3 to generate network flows and measuring L3 cache miss rates via perf, it seems that changing the MSR settings with wrmsr 0xc8b is not increasing the IIO_LLC_WAYS allocation as expected.

Could you provide guidance on whether adjusting 0xc8b for this model is indeed effective for increasing DDIO allocation within the LLC?

If there is an alternative method or a specific MSR configuration applicable to the Intel Xeon Gold 6354, I would appreciate any information or insights on how to properly increase the DDIO portion of the LLC cache.

Thank you very much for your assistance.

Best regards.

[TravisStacy]

Hello!

Thank you for sharing your detailed setup and troubleshooting process—it's clear you've put a lot of thought into optimizing DDIO allocation within the LLC. Adjusting MSR settings can indeed be complex, especially given the unique architecture of the Intel Xeon Gold 6354.

In similar cases, users have found that adjusting the IIO_LLC_WAYS using the 0xc8b register may not have the intended effect due to model-specific configurations. It may be worth investigating if this MSR behaves differently on the Ice Lake architecture of your processor. One approach to consider is checking for firmware or BIOS settings that could impact MSR-based adjustments, as these might override direct MSR modifications. Alternatively, exploring other MSR registers that control LLC allocations for your specific platform could yield better results.

It could also help to consult Intel’s official documentation or reach out to Intel support for confirmation on DDIO allocations specific to the Xeon Gold 6354. They may offer insights into MSR registers or BIOS settings that directly impact DDIO on this model.

Thanks again for bringing up such a fascinating challenge, and best of luck—hoping this leads you closer to a solution!