Re: [PATCH v15 5/6] rust: time: Add wrapper for fsleep() function

["Arnd Bergmann" <arnd@arndb.de>]

On Tue, Apr 29, 2025, at 15:17, FUJITA Tomonori wrote:
> On Mon, 28 Apr 2025 20:16:47 +0200 Andreas Hindborg <a.hindborg@kernel.org> wrote:
>      /// Return the number of milliseconds in the [`Delta`].
>      #[inline]
> -    pub const fn as_millis(self) -> i64 {
> -        self.as_nanos() / NSEC_PER_MSEC
> +    pub fn as_millis(self) -> i64 {
> +        math64::div64_s64(self.as_nanos(), NSEC_PER_MSEC)
>      }
>  }

I think simply calling ktime_to_ms()/ktime_to_us() should result
in reasonably efficient code, since the C version is able to
convert the constant divisor into a multiply/shift operation.

div64_s64() itself is never optimized for constant arguments since
the C version is not inline, if any driver needs those, this is
better done open-coded so hopefully it gets caught in review
when this is called in a fast path.

       Arnd