Should RAID-related features be built as modules?

[jessbo]

I was watching my RPi4 (using linux-raspberrypi4) boot with the serial console up and noticed there's a ~2.5 second boot delay.

$this->bbcode_second_pass_code('', '
[ 0.918528] raid6: neonx8 gen() 1000 MB/s
[ 1.088614] raid6: neonx8 xor() 883 MB/s
[ 1.258748] raid6: neonx4 gen() 1535 MB/s
[ 1.428878] raid6: neonx4 xor() 996 MB/s
[ 1.599030] raid6: neonx2 gen() 1163 MB/s
[ 1.769150] raid6: neonx2 xor() 963 MB/s
[ 1.939304] raid6: neonx1 gen() 760 MB/s
[ 2.109389] raid6: neonx1 xor() 722 MB/s
[ 2.279626] raid6: int32x8 gen() 349 MB/s
[ 2.449625] raid6: int32x8 xor() 237 MB/s
[ 2.619716] raid6: int32x4 gen() 334 MB/s
[ 2.789891] raid6: int32x4 xor() 267 MB/s
[ 2.959949] raid6: int32x2 gen() 313 MB/s
[ 3.130094] raid6: int32x2 xor() 245 MB/s
[ 3.300358] raid6: int32x1 gen() 212 MB/s
[ 3.470231] raid6: int32x1 xor() 187 MB/s
[ 3.474547] raid6: using algorithm neonx4 gen() 1535 MB/s
[ 3.480014] raid6: .... xor() 996 MB/s, rmw enabled
[ 3.484947] raid6: using neon recovery algorithm
')

This seems to be coming from $this->bbcode_second_pass_code('', 'CONFIG_RAID6_PQ_BENCHMARK=y'). There's no RAID going on at all on this system, so this behavior is quite undesired. Considering the SoC/embedded nature of the distro, is there any reason to keep building the RAID-related features as built-ins as opposed to building as modules?

[graysky]

I think that option is pulled in by another from the defconfig. There does not appear to be a way to make it a module. Perhaps there is a kernel parameter you can add to /boot/cmdline.txt to disable it? I don't know if disabling it in the kernel itself is wise given what some people do with these RPis. Implications for BTRFS and RAID if I am not mistaken.

[jessbo]

It was my assumption that this would only be run when the raid456 module was loaded, but that is not the case. Even as an unloaded module the benchmark still runs at boot. Still, for science, I did compile a kernel with it disabled:

$this->bbcode_second_pass_code('', '
[ 0.743630] raid6: using algorithm neonx8 gen() 0 MB/s
[ 0.748831] raid6: .... xor() 0 MB/s, rmw enabled
[ 0.753640] raid6: using neon recovery algorithm
')

So, guess I'll just live with it.