On Wed, 14 May 2014, Arnd Bergmann wrote: > On Wednesday 14 May 2014 14:21:48 Thomas Gleixner wrote: > > > > So in the 32-on-64 case we'll have two compat variants: > > > > SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, > > struct timespec __user *, utime, u32 __user *, uaddr2, > > u32, val3) > > > > COMPAT_SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, > > struct compat_timespec __user *, utime, u32 __user *, uaddr2, > > u32, val3) > > > > COMPAT_SYSCALL_DEFINE6(futex64, u32 __user *, uaddr, int, op, u32, val, > > struct timespec64 __user *, utime, u32 __user *, uaddr2, > > u32, val3) > > > > The native 64bit futex64 syscall is mapped to futex. > > I was actually hoping that we could map the compat futex64 to futex > as well here, since 64-bit timespec and compat timespec64 would be > the same structure. Right, that might work with this one, but not for anything which has a pointer to a timespec and some other argument based on long. > > I'm curious, whether quite some code, like high frequency timestamps > > wouldn't be better of with a strict 64 bit nanosecond granular time > > represenation. > > At least in the kernel, I think ktime_t is already the right type > to use on both 64-bit and 32-bit architectures as it can be slow to > extract the seconds portion of 64-bit nanoseconds on a 32-bit machine. On some of them yes. On i386 the u64 nsec ktime_t variant is way more efficient. > FWIW, 64-bit ns gives us 584 years worth of nanoseconds, which > means none of us or the people we know will be around before this > becomes a problem ;-) Indeed. > For the user interface, we can decide which representation to use > for each syscall individually depending on the needs. We should just > not have to many different variants. I was going for timespec64 > just because that would allow us to keep the 64-bit kernel ABI > unchanged. Right. It's the way of least resistance. If there are desires from user space to have a new format instead of blindly timespec64 for certain syscalls, we should really think discuss that on a case by case basis. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
