linux-kernel - Re: [PATCH v8 3/7] rust: time: Introduce Instant type

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Message-ID: <CAH5fLggz0t3wTxSNUw9oVBDbR_PSWpQysaSSt6drd7vw8AXQfw@mail.gmail.com>
Date: Thu, 16 Jan 2025 10:32:45 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>, 
	rust-for-linux@...r.kernel.org, netdev@...r.kernel.org, andrew@...n.ch, 
	hkallweit1@...il.com, tmgross@...ch.edu, ojeda@...nel.org, 
	alex.gaynor@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, a.hindborg@...sung.com, anna-maria@...utronix.de, 
	frederic@...nel.org, tglx@...utronix.de, arnd@...db.de, jstultz@...gle.com, 
	sboyd@...nel.org, mingo@...hat.com, peterz@...radead.org, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com
Subject: Re: [PATCH v8 3/7] rust: time: Introduce Instant type

On Thu, Jan 16, 2025 at 5:42 AM FUJITA Tomonori
<fujita.tomonori@...il.com> wrote:
>
> Introduce a type representing a specific point in time. We could use
> the Ktime type but C's ktime_t is used for both timestamp and
> timedelta. To avoid confusion, introduce a new Instant type for
> timestamp.
>
> Rename Ktime to Instant and modify their methods for timestamp.
>
> Implement the subtraction operator for Instant:
>
> Delta = Instant A - Instant B
>
> The operation never overflows (Instant ranges from 0 to
> `KTIME_MAX`).
>
> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> ---
>  rust/kernel/time.rs | 48 +++++++++++++++------------------------------
>  1 file changed, 16 insertions(+), 32 deletions(-)
>
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 55a365af85a3..da54a70f8f1f 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -31,59 +31,43 @@ pub fn msecs_to_jiffies(msecs: Msecs) -> Jiffies {
>      unsafe { bindings::__msecs_to_jiffies(msecs) }
>  }
>
> -/// A Rust wrapper around a `ktime_t`.
> +/// A specific point in time.
>  #[repr(transparent)]
>  #[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord)]
> -pub struct Ktime {
> +pub struct Instant {
> +    // Range from 0 to `KTIME_MAX`.
>      inner: bindings::ktime_t,
>  }
>
> -impl Ktime {
> -    /// Create a `Ktime` from a raw `ktime_t`.
> +impl Instant {
> +    /// Create a `Instant` from a raw `ktime_t`.
>      #[inline]
> -    pub fn from_raw(inner: bindings::ktime_t) -> Self {
> +    fn from_raw(inner: bindings::ktime_t) -> Self {
>          Self { inner }
>      }

Please keep this function public.

>      /// Get the current time using `CLOCK_MONOTONIC`.
>      #[inline]
> -    pub fn ktime_get() -> Self {
> +    pub fn now() -> Self {
>          // SAFETY: It is always safe to call `ktime_get` outside of NMI context.
>          Self::from_raw(unsafe { bindings::ktime_get() })
>      }
>
> -    /// Divide the number of nanoseconds by a compile-time constant.
>      #[inline]
> -    fn divns_constant<const DIV: i64>(self) -> i64 {
> -        self.to_ns() / DIV
> -    }
> -
> -    /// Returns the number of nanoseconds.
> -    #[inline]
> -    pub fn to_ns(self) -> i64 {
> -        self.inner
> -    }
> -
> -    /// Returns the number of milliseconds.
> -    #[inline]
> -    pub fn to_ms(self) -> i64 {
> -        self.divns_constant::<NSEC_PER_MSEC>()
> +    /// Return the amount of time elapsed since the `Instant`.
> +    pub fn elapsed(&self) -> Delta {

Nit: This places the #[inline] marker before the documentation. Please
move it after to be consistent.

Alice