diff options
| author | Dao Lu | 2022-06-20 13:15:25 -0700 |
|---|---|---|
| committer | Palmer Dabbelt | 2022-08-11 08:03:49 -0700 |
| commit | 8eb060e10185cfc97ef0200d197ec246ba0f9f8c (patch) | |
| tree | 5d72c5ef54b14b6b84b202ceae056cb401cf4284 /arch/riscv/include/asm/vdso | |
| parent | 3aefb2ee5bdd4a8976298415a5a017bf9844bfd5 (diff) | |
arch/riscv: add Zihintpause support
Implement support for the ZiHintPause extension.
The PAUSE instruction is a HINT that indicates the current hart’s rate
of instruction retirement should be temporarily reduced or paused.
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dao Lu <daolu@rivosinc.com>
[Palmer: Some minor merge conflicts.]
Link: https://lore.kernel.org/all/20220620201530.3929352-1-daolu@rivosinc.com/
Link: https://lore.kernel.org/all/20220811053356.17375-1-palmer@rivosinc.com/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv/include/asm/vdso')
| -rw-r--r-- | arch/riscv/include/asm/vdso/processor.h | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/arch/riscv/include/asm/vdso/processor.h b/arch/riscv/include/asm/vdso/processor.h index 134388cbaaa1..1e4f8b4aef79 100644 --- a/arch/riscv/include/asm/vdso/processor.h +++ b/arch/riscv/include/asm/vdso/processor.h @@ -4,15 +4,30 @@ #ifndef __ASSEMBLY__ +#include <linux/jump_label.h> #include <asm/barrier.h> +#include <asm/hwcap.h> static inline void cpu_relax(void) { + if (!static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_ZIHINTPAUSE])) { #ifdef __riscv_muldiv - int dummy; - /* In lieu of a halt instruction, induce a long-latency stall. */ - __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy)); + int dummy; + /* In lieu of a halt instruction, induce a long-latency stall. */ + __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy)); #endif + } else { + /* + * Reduce instruction retirement. + * This assumes the PC changes. + */ +#ifdef __riscv_zihintpause + __asm__ __volatile__ ("pause"); +#else + /* Encoding of the pause instruction */ + __asm__ __volatile__ (".4byte 0x100000F"); +#endif + } barrier(); } |