diff options
| author | Evan Green <evan@rivosinc.com> | 2023-04-07 16:11:01 -0700 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2023-04-18 15:48:16 -0700 |
| commit | 62a31d6e38bd0faef7c956b358d651f7bdc4ae0c (patch) | |
| tree | 87f6468aa566a9d30fe225fa1e444e64cb387dff /arch/riscv/include/uapi | |
| parent | 00e76e2c6a2bd3976d44d4a1fdd0b7a3c2566607 (diff) | |
RISC-V: hwprobe: Support probing of misaligned access performance
This allows userspace to select various routines to use based on the
performance of misaligned access on the target hardware.
Rather than adding DT bindings, this change taps into the alternatives
mechanism used to probe CPU errata. Add a new function pointer alongside
the vendor-specific errata_patch_func() that probes for desirable errata
(otherwise known as "features"). Unlike the errata_patch_func(), this
function is called on each CPU as it comes up, so it can save
feature information per-CPU.
The T-head C906 has fast unaligned access, both as defined by GCC [1],
and in performing a basic benchmark, which determined that byte copies
are >50% slower than a misaligned word copy of the same data size (source
for this test at [2]):
bytecopy size f000 count 50000 offset 0 took 31664899 us
wordcopy size f000 count 50000 offset 0 took 5180919 us
wordcopy size f000 count 50000 offset 1 took 13416949 us
[1] https://github.com/gcc-mirror/gcc/blob/master/gcc/config/riscv/riscv.cc#L353
[2] https://pastebin.com/EPXvDHSW
Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Evan Green <evan@rivosinc.com>
Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Paul Walmsley <paul.walmsley@sifive.com>
Link: https://lore.kernel.org/r/20230407231103.2622178-5-evan@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv/include/uapi')
| -rw-r--r-- | arch/riscv/include/uapi/asm/hwprobe.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h index 398e08f7e083..8d745a4ad8a2 100644 --- a/arch/riscv/include/uapi/asm/hwprobe.h +++ b/arch/riscv/include/uapi/asm/hwprobe.h @@ -25,6 +25,13 @@ struct riscv_hwprobe { #define RISCV_HWPROBE_KEY_IMA_EXT_0 4 #define RISCV_HWPROBE_IMA_FD (1 << 0) #define RISCV_HWPROBE_IMA_C (1 << 1) +#define RISCV_HWPROBE_KEY_CPUPERF_0 5 +#define RISCV_HWPROBE_MISALIGNED_UNKNOWN (0 << 0) +#define RISCV_HWPROBE_MISALIGNED_EMULATED (1 << 0) +#define RISCV_HWPROBE_MISALIGNED_SLOW (2 << 0) +#define RISCV_HWPROBE_MISALIGNED_FAST (3 << 0) +#define RISCV_HWPROBE_MISALIGNED_UNSUPPORTED (4 << 0) +#define RISCV_HWPROBE_MISALIGNED_MASK (7 << 0) /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */ #endif |