diff options
| author | Vincent Chen <vincent.chen@sifive.com> | 2020-06-09 22:14:48 +0800 |
|---|---|---|
| committer | Palmer Dabbelt <palmerdabbelt@google.com> | 2020-06-10 19:47:16 -0700 |
| commit | ad5d1122b82fbd6a816d1b9d26ee01a6dbc2d757 (patch) | |
| tree | 5e78643855b7be7a1bcffc4c7ee2769323ab181f /arch/riscv/kernel/vdso/Makefile | |
| parent | 05589dde649cd954a122b0ebb2cbe4ade8a80e98 (diff) | |
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>
Diffstat (limited to 'arch/riscv/kernel/vdso/Makefile')
| -rw-r--r-- | arch/riscv/kernel/vdso/Makefile | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile index 4c8b2a4a6a70..38ba55b0eb9d 100644 --- a/arch/riscv/kernel/vdso/Makefile +++ b/arch/riscv/kernel/vdso/Makefile @@ -1,12 +1,14 @@ # SPDX-License-Identifier: GPL-2.0-only # Copied from arch/tile/kernel/vdso/Makefile +# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before +# the inclusion of generic Makefile. +ARCH_REL_TYPE_ABS := R_RISCV_32|R_RISCV_64|R_RISCV_JUMP_SLOT +include $(srctree)/lib/vdso/Makefile # Symbols present in the vdso vdso-syms = rt_sigreturn ifdef CONFIG_64BIT -vdso-syms += gettimeofday -vdso-syms += clock_gettime -vdso-syms += clock_getres +vdso-syms += vgettimeofday endif vdso-syms += getcpu vdso-syms += flush_icache @@ -14,6 +16,10 @@ vdso-syms += flush_icache # Files to link into the vdso obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o +ifneq ($(c-gettimeofday-y),) + CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y) +endif + # Build rules targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds vdso-dummy.o obj-vdso := $(addprefix $(obj)/, $(obj-vdso)) |