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

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_VDSOCLOCKSOURCE_H
#define __ASM_VDSOCLOCKSOURCE_H

#define VDSO_ARCH_CLOCKMODES	\
	VDSO_CLOCKMODE_ARCHTIMER

#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			`/* SPDX-License-Identifier: GPL-2.0 */`
			`#ifndef __ASM_VDSOCLOCKSOURCE_H`
			`#define __ASM_VDSOCLOCKSOURCE_H`

			`#define VDSO_ARCH_CLOCKMODES \`
			`VDSO_CLOCKMODE_ARCHTIMER`

			`#endif`