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System

The tailored kernel

The linux-tkg kernel patched for the BC-250, the boot parameters and the kernels to avoid.

The heart of SkillFishOS’s optimizations is a custom-built kernel for the BC-250, based on linux-tkg — a build recipe from the Frogging Family that applies performance- and gaming-oriented patches.

Version and patches

The SkillFishOS kernel is version 7.2.0-skillfishos (the 7.0 and 7.1 series are end of life). On top of the standard linux-tkg patches it includes:

  • the BC-250 frequency-unlock patch (range 350–2230 MHz);
  • the 40-CU patch that enables all of the GPU’s Compute Units;
  • a custom RDSEED-quiet patch that silences a noisy kernel message on this hardware.

The kernel package (image + headers) is published as a release and is held (apt-mark hold) so that a Debian update can’t replace it with an unsuitable kernel. It is the default kernel in GRUB.

Boot parameters (cmdline)

The kernel command line is configured as follows, and every parameter has a precise reason:

mitigations=off
split_lock_detect=off
ttm.pages_limit=1572864
ttm.page_pool_size=1572864
Parameter What it does
mitigations=off disables Spectre/Meltdown mitigations to maximize performance (an acceptable choice on a home console)
ttm.pages_limit / ttm.page_pool_size the GTT ceiling, counted in 4 KiB pages: 1572864 = 6 GiB, so Vulkan sees ~13 GiB across VRAM and GTT (useful for AI). This used to be amdgpu.gttsize, deprecated since kernel 7.x: with both set the driver obeys that one and says so at every boot
split_lock_detect=off disables the split lock detector, which otherwise throttles processes doing unaligned atomic accesses (games and emulators do)

What about DisplayPort? The BC-250’s HPD is broken (see hardware), but SkillFishOS does not use the video=DP-1:e parameter: the skillfish-dp-hotswap service watches the EDID and re-enables the output when the monitor comes back. That also covers switching the monitor on after the board, which the parameter alone does not.

Live Compute Units. SkillFishOS no longer uses the amdgpu.bc250_cc_write_mode=3 parameter (which locked 40 CU at boot and blocked runtime changes). The system now boots at the driver baseline (24 CU) and a service routes the 40 CUs live at startup; you can change them without a reboot from the Tuner. See GPU and overclock.

Kernels to avoid

Not all recent kernels work well on this hardware. In particular the 6.15.0–6.15.6 and 6.17.8–6.17.10 series are known to be problematic and should be avoided. SkillFishOS ships its own tested kernel precisely to avoid these regressions — see Updates.

IOMMU

As noted on the hardware page, the IOMMU must never be enabled on the BC-250: it is unstable. The kernel always boots with IOMMU disabled.

Why our own kernel and not XanMod or stock

  • The Debian stock kernel lacks the BC-250 patches (frequency unlock, 40 CU) and follows the regressions above.
  • linux-tkg makes it easy to apply the custom patches and to pick gaming-oriented schedulers and options.
  • Building it ourselves means we update the kernel only when a new version brings real benefits and after testing it on the hardware.

Sources