diff options
| author | Kuan-Wei Chiu <visitorckw@gmail.com> | 2025-06-06 16:47:57 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-07-20 05:08:28 +0300 |
| commit | 26b537edc533058c48f6351569d676703d7d1af3 (patch) | |
| tree | 19d0cd1168dc03d6b24dbb458038f3344c9f5ed1 | |
| parent | b3d5fd6f82dde8c906dc2a587003a44252ae5eae (diff) | |
| download | linux-26b537edc533058c48f6351569d676703d7d1af3.tar.xz | |
riscv: optimize gcd() code size when CONFIG_RISCV_ISA_ZBB is disabled
The binary GCD implementation depends on efficient ffs(), which on RISC-V
requires hardware support for the Zbb extension. When
CONFIG_RISCV_ISA_ZBB is not enabled, the kernel will never use binary GCD,
as runtime logic will always fall back to the odd-even implementation.
To avoid compiling unused code and reduce code size, select
CONFIG_CPU_NO_EFFICIENT_FFS when CONFIG_RISCV_ISA_ZBB is not set.
$ ./scripts/bloat-o-meter ./lib/math/gcd.o.old ./lib/math/gcd.o.new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-274 (-274)
Function old new delta
gcd 360 86 -274
Total: Before=384, After=110, chg -71.35%
Link: https://lkml.kernel.org/r/20250606134758.1308400-3-visitorckw@gmail.com
Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Acked-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Ching-Chun (Jim) Huang <jserv@ccns.ncku.edu.tw>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | arch/riscv/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index d71ea0f4466f..1736768426ec 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -97,6 +97,7 @@ config RISCV select CLINT_TIMER if RISCV_M_MODE select CLONE_BACKWARDS select COMMON_CLK + select CPU_NO_EFFICIENT_FFS if !RISCV_ISA_ZBB select CPU_PM if CPU_IDLE || HIBERNATION || SUSPEND select EDAC_SUPPORT select FRAME_POINTER if PERF_EVENTS || (FUNCTION_TRACER && !DYNAMIC_FTRACE) |