On Mon, Jun 09, 2025 at 09:40:40AM +0200, Ingo Molnar wrote: > > * Eric Biggers <ebigg...@kernel.org> wrote: > > > This series is also available at: > > > > git fetch > > https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git > > lib-crc-arch-v2 > > > > This series improves how lib/crc supports arch-optimized code. First, > > instead of the arch-optimized CRC code being in arch/$(SRCARCH)/lib/, it > > will now be in lib/crc/$(SRCARCH)/. Second, the API functions (e.g. > > crc32c()), arch-optimized functions (e.g. crc32c_arch()), and generic > > functions (e.g. crc32c_base()) will now be part of a single module for > > each CRC type, allowing better inlining and dead code elimination. The > > second change is made possible by the first. > > > > As an example, consider CONFIG_CRC32=m on x86. We'll now have just > > crc32.ko instead of both crc32-x86.ko and crc32.ko. The two modules > > were already coupled together and always both got loaded together via > > direct symbol dependency, so the separation provided no benefit. > > > > Note: later I'd like to apply the same design to lib/crypto/ too, where > > often the API functions are out-of-line so this will work even better. > > In those cases, for each algorithm we currently have 3 modules all > > coupled together, e.g. libsha256.ko, libsha256-generic.ko, and > > sha256-x86.ko. We should have just one, inline things properly, and > > rely on the compiler's dead code elimination to decide the inclusion of > > the generic code instead of manually setting it via kconfig. > > > > Having arch-specific code outside arch/ was somewhat controversial when > > Zinc proposed it back in 2018. But I don't think the concerns are > > warranted. It's better from a technical perspective, as it enables the > > improvements mentioned above. This model is already successfully used > > in other places in the kernel such as lib/raid6/. The community of each > > architecture still remains free to work on the code, even if it's not in > > arch/. At the time there was also a desire to put the library code in > > the same files as the old-school crypto API, but that was a mistake; now > > that the library is separate, that's no longer a constraint either. > > > > Changed in v2: > > - Fixed build warning on architectures without any optimized CRC code > > - Fixed build warning in sparc/crc32.h by removing pr_fmt > > - Moved fallback definitions of crc32*_arch back into arch files > > - Remove ARCH_HAS_CRC* symbols at end of series instead of beginning, > > so that they're not removed until they're no longer being selected > > - Slightly improved some commit messages > > - Rebased onto other pending lib/crc changes > > > > Eric Biggers (12): > > lib/crc: move files into lib/crc/ > > lib/crc: prepare for arch-optimized code in subdirs of lib/crc/ > > lib/crc/arm: migrate arm-optimized CRC code into lib/crc/ > > lib/crc/arm64: migrate arm64-optimized CRC code into lib/crc/ > > lib/crc/loongarch: migrate loongarch-optimized CRC code into lib/crc/ > > lib/crc/mips: migrate mips-optimized CRC code into lib/crc/ > > lib/crc/powerpc: migrate powerpc-optimized CRC code into lib/crc/ > > lib/crc/riscv: migrate riscv-optimized CRC code into lib/crc/ > > lib/crc/s390: migrate s390-optimized CRC code into lib/crc/ > > lib/crc/sparc: migrate sparc-optimized CRC code into lib/crc/ > > lib/crc/x86: migrate x86-optimized CRC code into lib/crc/ > > lib/crc: remove ARCH_HAS_* kconfig symbols > > For the movement of the x86 bits: > > Acked-by: Ingo Molnar <mi...@kernel.org> > > > rename {arch/s390/lib => lib/crc/s390}/crc32be-vx.c (100%) > > rename {arch/s390/lib => lib/crc/s390}/crc32le-vx.c (100%) > > rename arch/sparc/lib/crc32.c => lib/crc/sparc/crc32.h (60%) > > rename {arch/sparc/lib => lib/crc/sparc}/crc32c_asm.S (100%) > > create mode 100644 lib/crc/tests/Makefile > > rename lib/{ => crc}/tests/crc_kunit.c (100%) > > rename {arch/x86/lib => lib/crc/x86}/crc-pclmul-consts.h (100%) > > rename {arch/x86/lib => lib/crc/x86}/crc-pclmul-template.S (100%) > > rename {arch/x86/lib => lib/crc/x86}/crc-pclmul-template.h (100%) > > rename arch/x86/lib/crc-t10dif.c => lib/crc/x86/crc-t10dif.h (56%) > > rename {arch/x86/lib => lib/crc/x86}/crc16-msb-pclmul.S (100%) > > rename {arch/x86/lib => lib/crc/x86}/crc32-pclmul.S (100%) > > One small namespace suggestion: wouldn't it be better to move the arch > support code to lib/crc/arch/, instead of lib/crc/? That way any > generic code will stand out better and architecture directories don't > crowd out what is supposed to be generic code.
I don't think that yet another level of directories would provide much value here. The only non-arch subdirectory of lib/crc/ is "tests", so it's not like there are a lot of subdirectories that could be confused with arch names. - Eric
