Messages in this thread | | | Date | Thu, 11 Apr 2024 11:19:05 -0700 | From | Boqun Feng <> | Subject | Re: [PATCH v2] rust: time: add Ktime |
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On Thu, Apr 11, 2024 at 06:21:43PM +0200, Alice Ryhl wrote: > On Thu, Apr 11, 2024 at 5:57 PM Boqun Feng <boqun.feng@gmail.com> wrote: > > > > On Fri, Mar 22, 2024 at 08:59:38AM +0000, Alice Ryhl wrote: > > > + /// 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, > > We enable overflow checks even on release mode right now. But I don't
Oh, I was missing that, then we actually have to skip the overflow checking with wrapping_sub() to mirror what C side does, for performance reasons and for avoiding panics.
Regards, Boqun
> understand this nit because we only have an overflow condition if the > two ktimes differ by more than 2^31, and if that happens then that's a > *legitimate* overflow that we would want to catch. Or is there > something I am missing? > > Alice
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