Re: [PATCH] vfs: replace current_kernel_time64 with ktime equivalent

[Andi Kleen <ak@linux.intel.com>]

Arnd Bergmann <arnd@arndb.de> writes:
>
> To clarify: current_kernel_time() uses at most millisecond resolution rather
> than microsecond, as tkr_mono.xtime_nsec only gets updated during the
> timer tick.

Ah you're right. I remember now: the motivation was to make sure there
is basically no overhead. In some setups the full gtod can be rather
slow, particularly if it falls back to some crappy timer.

I think it would be ok if it falls back to jiffies if TSC or a similar
fast timer doesn't work. But the function you're using likely
doesn't do that?

> Has that time scale changed over the past 16 years as CPUs got faster
> (and system call entry times slower down again with recent changes)?

Maybe a bit, but not substantially.



-Andi