Am Dienstag, den 11.12.2012, 11:27 -0800 schrieb John Stultz: > On 12/11/2012 08:11 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. > Very cool. There have been similar implementations of this patch over > the years, but they were all bit more hackish then this. > Thanks, i think it is not more hackish than the x86 64 code.
> > > 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. > Although the ACPI PM timer requires port-io which would need tweaking to > allow normal users to access it. And I'm not sure if the performance > would be much improved, as the port-io probably dominates the > performance cost. > It was only an idea. I think it would be easy to give the ioperm read for the ACPI Timer without breaking anything. > > The helper library to use the VDSO functions can be download at > > http://http://seibold.net/vdso.c > > The libary is very small, only 228 lines of code. Compile it with > > gcc -Wall -O3 -fpic vdso.c -lrt -shared -o libvdso.so > > and use it with LD_PRELOAD=<path>/libvdso.so > > > > This kind of helper must be integrated into glibc, for x86 64-bit and > > PowerPC it is already there. > > > A few notes below... > > > > diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h > > index 59c6c40..45ba688 100644 > > --- a/arch/x86/include/asm/compat.h > > +++ b/arch/x86/include/asm/compat.h > > @@ -295,6 +295,10 @@ static inline compat_uptr_t ptr_to_compat(void __user > > *uptr) > > > > static inline void __user *arch_compat_alloc_user_space(long len) > > { > > +#ifdef CONFIG_X86_32 > > + struct pt_regs *regs = task_pt_regs(current); > > + return (void __user *)regs->sp - len; > > +#else > > compat_uptr_t sp; > > > > if (test_thread_flag(TIF_IA32)) { > > @@ -305,6 +309,7 @@ static inline void __user > > *arch_compat_alloc_user_space(long len) > > } > > > > return (void __user *)round_down(sp - len, 16); > > +#endif > > } > > This style of in-line ifdefs are ugly and hard to read. > > So instead of doing: > void myfunction (void) > { > #ifdef 32bits > 32_bit_implementation(); > #else > 64_bit_implementation(); > #endif > } > > Where possible, please do: > #ifdef 32bits > void myfunction1(void) > { > 32_bit implementation(); > } > void myfunction2(void) > { > .... > #else /*64 bit versions */ > void myfunction1(void) > { > 64_bit implementation(); > } > void myfunction2(void) > .... > #endif > > > diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c > > index 4df6c37..2dc6b72 100644 > > --- 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 > > } > > > > 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; > > } > Same point here. > > Will be fixed. > > diff --git a/arch/x86/vdso/vdso32/vclock_gettime.c > > b/arch/x86/vdso/vdso32/vclock_gettime.c > > new file mode 100644 > > index 0000000..c9a1909 > > --- /dev/null > > +++ b/arch/x86/vdso/vdso32/vclock_gettime.c > > @@ -0,0 +1,7 @@ > > +/* > > + * since vgtod layout differs between X86_64 and x86_32, it is not > > possible to > > + * provide a 32 bit vclock with a 64 bit kernel > > + */ > > +#ifdef CONFIG_X86_32 > > +#include "../vclock_gettime.c" > > +#endif > Could you expand a bit as to why a compat layer isn't possible? It seems > we could easily convert the vsyscall_gtod_data to a more explicit > arch-neutral size. Or is it the actual data page mapping? > This could be done in a subsequent patch. First i want not change to much, to make the review easier. Converting the vsyscall_gtod_data to arch neutral is not so easy, because the size of time_t, timezone and timespec differs. So currently 32 bit programs running under a 64 bit kernel will not get a VDSO with time functions. But real 32 bit kernel will provide it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/