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linux/arch/riscv/include/asm/vdso/processor.h

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riscv: use vDSO common flow to reduce the latency of the time-related functions Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-06-09 22:14:48 +08:00
/* SPDX-License-Identifier: GPL-2.0-only */
#ifndef __ASM_VDSO_PROCESSOR_H
#define __ASM_VDSO_PROCESSOR_H
#ifndef __ASSEMBLY__
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>
2022-06-20 13:15:25 -07:00
#include <linux/jump_label.h>
RISC-V: fix barrier() use in <vdso/processor.h> riscv's <vdso/processor.h> uses barrier() so it should include <asm/barrier.h> Fixes this build error: CC [M] drivers/net/ethernet/emulex/benet/be_main.o In file included from ./include/vdso/processor.h:10, from ./arch/riscv/include/asm/processor.h:11, from ./include/linux/prefetch.h:15, from drivers/net/ethernet/emulex/benet/be_main.c:14: ./arch/riscv/include/asm/vdso/processor.h: In function 'cpu_relax': ./arch/riscv/include/asm/vdso/processor.h:14:2: error: implicit declaration of function 'barrier' [-Werror=implicit-function-declaration] 14 | barrier(); This happens with a total of 5 networking drivers -- they all use <linux/prefetch.h>. rv64 allmodconfig now builds cleanly after this patch. Fixes fallout from: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive") Fixes: ad5d1122b82f ("riscv: use vDSO common flow to reduce the latency of the time-related functions") Reported-by: Andreas Schwab <schwab@linux-m68k.org> Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Arvind Sankar <nivedita@alum.mit.edu> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-11-16 17:39:51 -08:00
#include <asm/barrier.h>
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>
2022-06-20 13:15:25 -07:00
#include <asm/hwcap.h>
RISC-V: fix barrier() use in <vdso/processor.h> riscv's <vdso/processor.h> uses barrier() so it should include <asm/barrier.h> Fixes this build error: CC [M] drivers/net/ethernet/emulex/benet/be_main.o In file included from ./include/vdso/processor.h:10, from ./arch/riscv/include/asm/processor.h:11, from ./include/linux/prefetch.h:15, from drivers/net/ethernet/emulex/benet/be_main.c:14: ./arch/riscv/include/asm/vdso/processor.h: In function 'cpu_relax': ./arch/riscv/include/asm/vdso/processor.h:14:2: error: implicit declaration of function 'barrier' [-Werror=implicit-function-declaration] 14 | barrier(); This happens with a total of 5 networking drivers -- they all use <linux/prefetch.h>. rv64 allmodconfig now builds cleanly after this patch. Fixes fallout from: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive") Fixes: ad5d1122b82f ("riscv: use vDSO common flow to reduce the latency of the time-related functions") Reported-by: Andreas Schwab <schwab@linux-m68k.org> Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Arvind Sankar <nivedita@alum.mit.edu> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-11-16 17:39:51 -08:00
riscv: use vDSO common flow to reduce the latency of the time-related functions Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-06-09 22:14:48 +08:00
static inline void cpu_relax(void)
{
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>
2022-06-20 13:15:25 -07:00
if (!static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_ZIHINTPAUSE])) {
riscv: use vDSO common flow to reduce the latency of the time-related functions Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-06-09 22:14:48 +08:00
#ifdef __riscv_muldiv
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>
2022-06-20 13:15:25 -07:00
int dummy;
/* In lieu of a halt instruction, induce a long-latency stall. */
__asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
riscv: use vDSO common flow to reduce the latency of the time-related functions Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-06-09 22:14:48 +08:00
#endif
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>
2022-06-20 13:15:25 -07:00
} 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
}
riscv: use vDSO common flow to reduce the latency of the time-related functions Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-06-09 22:14:48 +08:00
barrier();
}
#endif /* __ASSEMBLY__ */
#endif /* __ASM_VDSO_PROCESSOR_H */
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