Vincent Chen ad5d1122b8 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>		2020-06-10 19:47:16 -07:00
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boot	riscv: K210: Add a built-in device tree	2020-05-18 11:38:06 -07:00
configs	riscv: K210: Update defconfig	2020-05-18 11:38:07 -07:00
include	riscv: use vDSO common flow to reduce the latency of the time-related functions	2020-06-10 19:47:16 -07:00
kernel	riscv: use vDSO common flow to reduce the latency of the time-related functions	2020-06-10 19:47:16 -07:00
lib	RISC-V Patches for the 5.7 Merge Window, Part 1	2020-04-09 10:51:30 -07:00
mm	RISC-V: Don't mark init section as non-executable	2020-06-09 19:11:26 -07:00
net	bpf, riscv: Optimize BPF_JSET BPF_K using andi on RV64	2020-05-06 09:48:15 +02:00
Kbuild	riscv: Allow device trees to be built into the kernel	2020-05-18 11:38:05 -07:00
Kconfig	riscv: use vDSO common flow to reduce the latency of the time-related functions	2020-06-10 19:47:16 -07:00
Kconfig.debug	RISC-V: Remove EARLY_PRINTK support	2018-12-17 10:23:46 -08:00
Kconfig.socs	riscv: K210: Add a built-in device tree	2020-05-18 11:38:06 -07:00
Makefile	RISC-V Patches for the 5.7 Merge Window, Part 1	2020-04-09 10:51:30 -07:00