On Tue, Dec 11, 2012 at 8:11 AM, <stef...@seibold.net> wrote:
> From: Stefani Seibold <stef...@seibold.net>
>
> This small patch add the functions vdso_gettimeofday(), vdso_clock_gettime()
> and vdso_time() support to the VDSO for x86 32-bit kernels.
>
> The reason to do this was to get a fast reliable time stamp. Many developers
> uses TSC to get a fast time time stamp, without knowing the pitfalls. VDSO
> time functions a fast and reliable way, because the kernel knows the best time
> source and the P- and C-state of the CPU.
>
> For x86 the vclock_gettime.c currently supports only the HPET and TSC timer,
> the ACPI timer should be easily to add with an other patch.
>
> The helper library to use the VDSO functions can be download at
> http://http://seibold.net/vdso.c
Wow -- another implementation. See Documentation/vDSO/parse_vdso.c.
(Also, I think your code will break if anyone ever strips the vdso.)
> --- a/arch/x86/vdso/vclock_gettime.c
> +++ b/arch/x86/vdso/vclock_gettime.c
> @@ -59,14 +59,23 @@ notrace static cycle_t vread_tsc(void)
>
> static notrace cycle_t vread_hpet(void)
> {
> +#ifdef CONFIG_X86_64
> return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + 0xf0);
> +#else
> + return readl(VVAR(vsyscall_hpet) + HPET_COUNTER);
> +#endif
> }
Is 0xf0 not equal to HPET_COUNTER?
>
> notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
> {
> long ret;
> +#ifdef CONFIG_X86_64
> asm("syscall" : "=a" (ret) :
> "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
> +#else
> + asm("int $0x80" : "=a" (ret) :
> + "a" (__NR_clock_gettime), "b" (clock), "c" (ts) : "memory");
> +#endif
> return ret;
> }
__kernel_vsyscall is probably much faster if you can figure out how to
call it from here :)
>
> @@ -74,15 +83,20 @@ notrace static long vdso_fallback_gtod(struct timeval
> *tv, struct timezone *tz)
> {
> long ret;
>
> +#ifdef CONFIG_X86_64
> asm("syscall" : "=a" (ret) :
> "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
> +#else
> + asm("int $0x80" : "=a" (ret) :
> + "a" (__NR_gettimeofday), "b" (tv), "c" (tz) : "memory");
> +#endif
> return ret;
> }
>
Ditto.
> --- a/arch/x86/vdso/vdso32/vdso32.lds.S
> +++ b/arch/x86/vdso/vdso32/vdso32.lds.S
> @@ -24,6 +24,16 @@ VERSION
> __kernel_vsyscall;
> __kernel_sigreturn;
> __kernel_rt_sigreturn;
> +#ifdef CONFIG_X86_32
> + clock_gettime;
> + __vdso_clock_gettime;
> + gettimeofday;
> + __vdso_gettimeofday;
> + gettimeofday;
> + __vdso_gettimeofday;
> + time;
> + __vdso_time;
> +#endif
Please remove the non-__vdso versions. They're not useful and x86-64
only has them for backwards compatibility.
> local: *;
> };
> }
> @@ -35,3 +45,8 @@ VDSO32_PRELINK = VDSO_PRELINK;
> VDSO32_vsyscall = __kernel_vsyscall;
> VDSO32_sigreturn = __kernel_sigreturn;
> VDSO32_rt_sigreturn = __kernel_rt_sigreturn;
> +#ifdef CONFIG_X86_32
> +VDSO32_clock_gettime = clock_gettime;
> +VDSO32_gettimeofday = gettimeofday;
> +VDSO32_time = time;
> +#endif
Yikes. What's this? (Just curious.)
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