Messages in this thread Patch in this message | | | Date | Thu, 11 Apr 2024 08:56:58 -0700 | From | Boqun Feng <> | Subject | Re: [PATCH v2] rust: time: add Ktime |
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On Fri, Mar 22, 2024 at 08:59:38AM +0000, Alice Ryhl wrote: > Introduce a wrapper around `ktime_t` with a few different useful > methods. > > Rust Binder will use these bindings to compute how many milliseconds a > transaction has been active for when dumping the current state of the > Binder driver. This replicates the logic in C Binder [1]. > > For a usage example in Rust Binder, see [2]. > > The `ktime_get` method cannot be safely called in NMI context. This > requirement is not checked by these abstractions, but it is intended > that klint [3] or a similar tool will be used to check it in the future. > > Link: https://lore.kernel.org/lkml/5ac8c0d09392290be789423f0dd78a520b830fab.1682333709.git.zhangchuang3@xiaomi.com/ [1] > Link: https://r.android.com/3004103 [2] > Link: https://rust-for-linux.com/klint [3] > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > Changes in v2: > - Mention that ktime_get cannot be safely called in NMI context. > - Link to v1: https://lore.kernel.org/r/20240320-rust-ktime_ms_delta-v1-1-ccb8672a0941@google.com > --- > rust/kernel/time.rs | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 60 insertions(+) > > diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs > index 25a896eed468..6811d5cadbd4 100644 > --- a/rust/kernel/time.rs > +++ b/rust/kernel/time.rs > @@ -5,6 +5,9 @@ > //! This module contains the kernel APIs related to time and timers that > //! have been ported or wrapped for usage by Rust code in the kernel. > > +/// The number of nanoseconds per millisecond. > +pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64; > + > /// The time unit of Linux kernel. One jiffy equals (1/HZ) second. > pub type Jiffies = core::ffi::c_ulong; > > @@ -18,3 +21,60 @@ pub fn msecs_to_jiffies(msecs: Msecs) -> Jiffies { > // matter what the argument is. > unsafe { bindings::__msecs_to_jiffies(msecs) } > } > + > +/// A Rust wrapper around a `ktime_t`. > +#[repr(transparent)] > +#[derive(Copy, Clone)] > +pub struct Ktime { > + inner: bindings::ktime_t, > +} > + > +impl Ktime { > + /// Create a `Ktime` from a raw `ktime_t`. > + #[inline] > + pub fn from_raw(inner: bindings::ktime_t) -> Self { > + Self { inner } > + } > + > + /// Get the current time using `CLOCK_MONOTONIC`. > + #[inline] > + pub fn ktime_get() -> 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>() > + } > +} > + > +/// Returns the number of milliseconds between two ktimes. > +#[inline] > +pub fn ktime_ms_delta(later: Ktime, earlier: Ktime) -> i64 { > + (later - earlier).to_ms() > +} > + > +impl core::ops::Sub for Ktime { > + type Output = Ktime; > + > + #[inline] > + fn sub(self, other: Ktime) -> Ktime { > + Self { > + inner: self.inner - other.inner,
Nit: although we use "Release mode" to compile Rust code in kernel, so i64 substraction behaves as 2's complement wrap, I think it's better we use wrapping_sub here: self.inner.wrapping_sub(other.inner)
however it's not a correctness issue for now, so with or without it, Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Regards, Boqun
> + } > + } > +} > > --- > base-commit: 768409cff6cc89fe1194da880537a09857b6e4db > change-id: 20240320-rust-ktime_ms_delta-74b00c9ab872 > > Best regards, > -- > Alice Ryhl <aliceryhl@google.com> >
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