diff options
| author | Jisheng Zhang <jszhang@kernel.org> | 2023-12-25 12:42:06 +0800 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-01-09 20:18:19 -0800 |
| commit | b6da6cbe13ebf24716438de71d50573b9f36f35d (patch) | |
| tree | e4e3bb3a5a97252d80d651c35c80e1d2342a696b /arch/riscv/Makefile | |
| parent | b85ea95d086471afb4ad062012a4d73cd328fa86 (diff) | |
riscv: introduce RISCV_EFFICIENT_UNALIGNED_ACCESS
Some riscv implementations such as T-HEAD's C906, C908, C910 and C920
support efficient unaligned access, for performance reason we want
to enable HAVE_EFFICIENT_UNALIGNED_ACCESS on these platforms. To
avoid performance regressions on other non efficient unaligned access
platforms, HAVE_EFFICIENT_UNALIGNED_ACCESS can't be globally selected.
To solve this problem, runtime code patching based on the detected
speed is a good solution. But that's not easy, it involves lots of
work to modify vairous subsystems such as net, mm, lib and so on.
This can be done step by step.
So let's take an easier solution: add support to efficient unaligned
access and hide the support under NONPORTABLE.
Now let's introduce RISCV_EFFICIENT_UNALIGNED_ACCESS which depends on
NONPORTABLE, if users know during config time that the kernel will be
only run on those efficient unaligned access hw platforms, they can
enable it. Obviously, generic unified kernel Image shouldn't enable it.
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20231225044207.3821-2-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv/Makefile')
| -rw-r--r-- | arch/riscv/Makefile | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile index a74be78678eb..ebbe02628a27 100644 --- a/arch/riscv/Makefile +++ b/arch/riscv/Makefile @@ -108,7 +108,9 @@ KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax) # unaligned accesses. While unaligned accesses are explicitly allowed in the # RISC-V ISA, they're emulated by machine mode traps on all extant # architectures. It's faster to have GCC emit only aligned accesses. +ifneq ($(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS),y) KBUILD_CFLAGS += $(call cc-option,-mstrict-align) +endif ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y) prepare: stack_protector_prepare |