Ard brought this to my attention in this patch [1]. I benchmarked this patch on the Nezha D1 (which does not contain Zba or Zbkb so it uses the default algorithm) by navigating through a large directory structure. I created a 1000-deep directory structure and then cd and ls through it. With this patch there was a 0.57% performance improvement.
[1] https://lore.kernel.org/lkml/CAMj1kXE4DJnwFejNWQu784GvyJO=agnrzuljsxiowx_e7nw...@mail.gmail.com/ Signed-off-by: Charlie Jenkins <char...@rivosinc.com> --- Changes in v10: - Use _AC() instead of just adding U to the end of a constant - Link to v9: https://lore.kernel.org/r/20250318-runtime_const_riscv-v9-0-ddd3534d3...@rivosinc.com Changes in v9: - Fix bug where stale register data may be used when an lui is replaced with a nop. In the following addiw, add to register x0 instead of the stale register to resolve. - Add locks for text_mutex before using patch_insn_write() - Link to v8: https://lore.kernel.org/r/20250305-runtime_const_riscv-v8-1-fa66f3468...@rivosinc.com Changes in v8: - Rebase to linux v6.14-rc5 - Link to v7: https://lore.kernel.org/r/20250218-runtime_const_riscv-v7-1-e43176315...@rivosinc.com Changes in v7: - Added benchmarking info - Added CONFIG_RISCV_ISA_ZBA and CONFIG_RISCV_ISA_ZBKB to check that the compiler supports the extensions. - Link to v6: https://lore.kernel.org/r/20250212-runtime_const_riscv-v6-1-3ef0146b3...@rivosinc.com Changes in v6: - .option arch only became officially supported by clang in version 17. Add a config to check that and guard the alternatives uses .option arch. - Link to v5: https://lore.kernel.org/r/20250203-runtime_const_riscv-v5-1-bc61736a3...@rivosinc.com Changes in v5: - Split instructions into 16-bit parcels to avoid alignment (Emil) - Link to v4: https://lore.kernel.org/r/20250130-runtime_const_riscv-v4-1-2d36c41b7...@rivosinc.com Changes in v4: - Add newlines after riscv32 assembler directives - Align instructions along 32-bit boundary (Emil) - Link to v3: https://lore.kernel.org/r/20250128-runtime_const_riscv-v3-1-11922989e...@rivosinc.com Changes in v3: - Leverage "pack" instruction for runtime_const_ptr() to reduce hot path by 3 instructions if Zbkb is supported. Suggested by Pasha Bouzarjomehri (pa...@rivosinc.com) - Link to v2: https://lore.kernel.org/r/20250127-runtime_const_riscv-v2-1-95ae7cf97...@rivosinc.com Changes in v2: - Treat instructions as __le32 and do proper conversions (Ben) - Link to v1: https://lore.kernel.org/r/20250127-runtime_const_riscv-v1-1-795b023ea...@rivosinc.com --- Charlie Jenkins (2): riscv: Move nop definition to insn-def.h riscv: Add runtime constant support arch/riscv/Kconfig | 22 +++ arch/riscv/include/asm/asm.h | 1 + arch/riscv/include/asm/ftrace.h | 1 - arch/riscv/include/asm/insn-def.h | 3 + arch/riscv/include/asm/runtime-const.h | 265 +++++++++++++++++++++++++++++++++ arch/riscv/kernel/ftrace.c | 6 +- arch/riscv/kernel/jump_label.c | 4 +- arch/riscv/kernel/vmlinux.lds.S | 3 + 8 files changed, 299 insertions(+), 6 deletions(-) --- base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b change-id: 20250123-runtime_const_riscv-6cd854ee2817 -- - Charlie
