64KB page size support?

#1

Hello, I would like to try using 64KB page size for performance reasons. However, if I enable them at the kernel (cix 6.10 acpi) configuration, my kernel panics during boot. Does a specific device rely on 4K pages, is it a kernel/driver bug or something completely different? As a side note, why does the board reset on a kernel panic, instead of hanging? As another side note, 64KB pages work on my Rock 5B and produce some nice performance improvement.

#2

I built 6.16.0 & 6.16.3 kernels with 64k pages (+5.7% performance over 16k pages, and the improvement from 4k to 16k is the larger increase!) and had no problems.

(Although the low-level driver support is currently barely there in mainline kernels, sadly)

#3

Thanks for your response,

I was using the cix kernel (version 6.6.10) because of the lack of drivers. Does the mainline kernel support the pcie (and the nvme slot), the UART and the ethernet? I need them for basic testing. Also, are you using a specific .config and boot command parameters? Finally, how did you measure the performance?

Thanks in advance

#4

The mainline kernel supports all these things as long as you boot in ACPI mode - refer to this page for more details.

#5

Yup, ACPI is needed for PCIe to work it turns out (for an LSI HBA in any case), and the other mentioned hardware does work. Many other lower-level devices plus NPU, GPU, etc. are not supported, however.

I hand-tuned a custom .config with only the present hardware configured, no special boot parameters.

The performance test was building the 6.16.0 kernel from scratch - a decent enough, repeatable task which takes long enough to give a representative result.

(But I’ve previously run much more in-depth benchmarks of Ampere, AWS Graviton, RK3588 & RPi systems - and the results track these, so I’m fairly confident they’re sound)