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 <[email protected]> --- 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/[email protected] Changes in v8: - Rebase to linux v6.14-rc5 - Link to v7: https://lore.kernel.org/r/[email protected] 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/[email protected] 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/[email protected] Changes in v5: - Split instructions into 16-bit parcels to avoid alignment (Emil) - Link to v4: https://lore.kernel.org/r/[email protected] Changes in v4: - Add newlines after riscv32 assembler directives - Align instructions along 32-bit boundary (Emil) - Link to v3: https://lore.kernel.org/r/[email protected] 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 ([email protected]) - Link to v2: https://lore.kernel.org/r/[email protected] Changes in v2: - Treat instructions as __le32 and do proper conversions (Ben) - Link to v1: https://lore.kernel.org/r/[email protected] --- 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 | 2 + 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, 298 insertions(+), 6 deletions(-) --- base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b change-id: 20250123-runtime_const_riscv-6cd854ee2817 -- - Charlie
