[PATCH] powerpc/vdso64: Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE
Michael Ellerman
mpe at ellerman.id.au
Thu Jul 20 23:18:26 AEST 2017
Santosh Sivaraj <santosh at fossix.org> writes:
> Current vDSO64 implementation does not have support for coarse
> clocks (CLOCK_MONOTONIC_COARSE, CLOCK_REALTIME_COARSE), for which it falls
> back to system call. Below is a benchmark of the difference in execution
> time with and without vDSO support.
Hi Santosh,
Great patch! Always good to see asm replaced with C.
> diff --git a/arch/powerpc/kernel/vdso64/gettime.c b/arch/powerpc/kernel/vdso64/gettime.c
> new file mode 100644
> index 0000000..01f411f
> --- /dev/null
> +++ b/arch/powerpc/kernel/vdso64/gettime.c
> @@ -0,0 +1,162 @@
...
> +static notrace int gettime_syscall_fallback(clockid_t clk_id,
> + struct timespec *tp)
> +{
> + register clockid_t id asm("r3") = clk_id;
> + register struct timespec *t asm("r4") = tp;
> + register int nr asm("r0") = __NR_clock_gettime;
> + register int ret asm("r3");
I guess this works. I've always been a bit nervous about register
variables TBH.
> + asm volatile("sc"
> + : "=r" (ret)
> + : "r"(nr), "r"(id), "r"(t)
> + : "memory");
Not sure we need the memory clobber?
It can clobber more registers than that though.
See: Documentation/powerpc/syscall64-abi.txt
> diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S b/arch/powerpc/kernel/vdso64/gettimeofday.S
> index 3820213..1258009 100644
> --- a/arch/powerpc/kernel/vdso64/gettimeofday.S
> +++ b/arch/powerpc/kernel/vdso64/gettimeofday.S
> @@ -51,85 +53,21 @@ V_FUNCTION_BEGIN(__kernel_gettimeofday)
...
> + stwu r1,-112(r1)
> + .cfi_register lr,r6
> + std r6,24(r1)
> + bl V_LOCAL_FUNC(kernel_clock_gettime)
> crclr cr0*4+so
Clearing CR0[SO] says that the syscall always succeeded.
What happens if you call this with a completely bogus clock id?
I think the solution is probably to do the syscall fallback in asm, and
everything else in C.
cheers
More information about the Linuxppc-dev
mailing list