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>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7c96149..128192e 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -12,6 +12,7 @@
config RISCV
def_bool y
+ select ARCH_CLOCKSOURCE_INIT
select ARCH_HAS_BINFMT_FLAT
select ARCH_HAS_DEBUG_VIRTUAL if MMU
select ARCH_HAS_DEBUG_WX
@@ -31,6 +32,7 @@
select GENERIC_ARCH_TOPOLOGY if SMP
select GENERIC_ATOMIC64 if !64BIT
select GENERIC_CLOCKEVENTS
+ select GENERIC_GETTIMEOFDAY if HAVE_GENERIC_VDSO
select GENERIC_IOREMAP
select GENERIC_IRQ_MULTI_HANDLER
select GENERIC_IRQ_SHOW
@@ -40,6 +42,7 @@
select GENERIC_SMP_IDLE_THREAD
select GENERIC_STRNCPY_FROM_USER if MMU
select GENERIC_STRNLEN_USER if MMU
+ select GENERIC_TIME_VSYSCALL if MMU && 64BIT
select HANDLE_DOMAIN_IRQ
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_KASAN if MMU && 64BIT
@@ -53,6 +56,7 @@
select HAVE_DMA_CONTIGUOUS if MMU
select HAVE_EBPF_JIT if MMU
select HAVE_FUTEX_CMPXCHG if FUTEX
+ select HAVE_GENERIC_VDSO if MMU && 64BIT
select HAVE_PCI
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
