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Message-ID: <87r0753nu7.fsf@kernel.org>
Date: Wed, 20 Nov 2024 16:51:44 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Lyude Paul" <lyude@...hat.com>
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "Anna-Maria Behnsen"
<anna-maria@...utronix.de>, "Frederic Weisbecker" <frederic@...nel.org>,
"Thomas Gleixner" <tglx@...utronix.de>, "Alex Gaynor"
<alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
<gary@...yguo.net>, Björn Roy Baron
<bjorn3_gh@...tonmail.com>, "Benno
Lossin" <benno.lossin@...ton.me>, "Alice Ryhl" <aliceryhl@...gle.com>,
"Trevor Gross" <tmgross@...ch.edu>, <rust-for-linux@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 11/13] rust: hrtimer: add `TimerMode`
"Lyude Paul" <lyude@...hat.com> writes:
> On Thu, 2024-10-17 at 15:04 +0200, Andreas Hindborg wrote:
>> Allow selection of timer mode by passing a `TimerMode` variant to
>> `Timer::new`.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>> ---
>> rust/kernel/hrtimer.rs | 88 +++++++++++++++++++++++++++++++++++++++++++++++---
>> 1 file changed, 84 insertions(+), 4 deletions(-)
>>
>> diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
>> index 2c1573e19576de93afc959d71e94173e2c1ed715..1674d1dcba39cc7ab82e1f189002afa365ee9341 100644
>> --- a/rust/kernel/hrtimer.rs
>> +++ b/rust/kernel/hrtimer.rs
>> @@ -38,12 +38,13 @@
>> /// # Invariants
>> ///
>> /// * `self.timer` is initialized by `bindings::hrtimer_init`.
>> -#[repr(transparent)]
>> #[pin_data]
>> #[repr(C)]
>> pub struct Timer<U> {
>> #[pin]
>> timer: Opaque<bindings::hrtimer>,
>> + // This field goes away when `bindings::hrtimer_setup` is added.
>> + mode: TimerMode,
>> _t: PhantomData<U>,
>> }
>>
>> @@ -56,7 +57,7 @@ unsafe impl<U> Sync for Timer<U> {}
>>
>> impl<T> Timer<T> {
>> /// Return an initializer for a new timer instance.
>> - pub fn new() -> impl PinInit<Self>
>> + pub fn new(mode: TimerMode) -> impl PinInit<Self>
>> where
>> T: TimerCallback,
>> {
>> @@ -70,7 +71,7 @@ pub fn new() -> impl PinInit<Self>
>> bindings::hrtimer_init(
>> place,
>> bindings::CLOCK_MONOTONIC as i32,
>> - bindings::hrtimer_mode_HRTIMER_MODE_REL,
>> + mode.into(),
>> );
>> }
>>
>> @@ -83,6 +84,7 @@ pub fn new() -> impl PinInit<Self>
>> // exclusive access.
>> unsafe { core::ptr::write(function, Some(T::CallbackTarget::run)) };
>> }),
>> + mode: mode,
>> _t: PhantomData,
>> })
>> }
>> @@ -330,7 +332,7 @@ unsafe fn start(self_ptr: *const Self, expires: Ktime) {
>> Self::c_timer_ptr(self_ptr).cast_mut(),
>> expires.to_ns(),
>> 0,
>> - bindings::hrtimer_mode_HRTIMER_MODE_REL,
>> + (*Self::raw_get_timer(self_ptr)).mode.into(),
>> );
>> }
>> }
>> @@ -362,6 +364,84 @@ fn from(value: TimerRestart) -> Self {
>> }
>> }
>>
>> +/// Operational mode of [`Timer`].
>> +#[derive(Clone, Copy)]
>> +pub enum TimerMode {
>> + /// Timer expires at the given expiration time.
>> + Absolute,
>> + /// Timer expires after the given expiration time interpreted as a duration from now.
>> + Relative,
>> + /// Timer does not move between CPU cores.
>> + Pinned,
>> + /// Timer handler is executed in soft irq context.
>> + Soft,
>> + /// Timer handler is executed in hard irq context.
>> + Hard,
>> + /// Timer expires at the given expiration time.
>> + /// Timer does not move between CPU cores.
>> + AbsolutePinned,
>> + /// Timer expires after the given expiration time interpreted as a duration from now.
>> + /// Timer does not move between CPU cores.
>> + RelativePinned,
>> + /// Timer expires at the given expiration time.
>> + /// Timer handler is executed in soft irq context.
>> + AbsoluteSoft,
>> + /// Timer expires after the given expiration time interpreted as a duration from now.
>> + /// Timer handler is executed in soft irq context.
>> + RelativeSoft,
>> + /// Timer expires at the given expiration time.
>> + /// Timer does not move between CPU cores.
>> + /// Timer handler is executed in soft irq context.
>> + AbsolutePinnedSoft,
>> + /// Timer expires after the given expiration time interpreted as a duration from now.
>> + /// Timer does not move between CPU cores.
>> + /// Timer handler is executed in soft irq context.
>> + RelativePinnedSoft,
>> + /// Timer expires at the given expiration time.
>> + /// Timer handler is executed in hard irq context.
>> + AbsoluteHard,
>> + /// Timer expires after the given expiration time interpreted as a duration from now.
>> + /// Timer handler is executed in hard irq context.
>> + RelativeHard,
>> + /// Timer expires at the given expiration time.
>> + /// Timer does not move between CPU cores.
>> + /// Timer handler is executed in hard irq context.
>> + AbsolutePinnedHard,
>> + /// Timer expires after the given expiration time interpreted as a duration from now.
>> + /// Timer does not move between CPU cores.
>> + /// Timer handler is executed in hard irq context.
>> + RelativePinnedHard,
>> +}
>> +
>> +impl From<TimerMode> for bindings::hrtimer_mode {
>> + fn from(value: TimerMode) -> Self {
>> + use bindings::*;
>> + match value {
>> + TimerMode::Absolute => hrtimer_mode_HRTIMER_MODE_ABS,
>> + TimerMode::Relative => hrtimer_mode_HRTIMER_MODE_REL,
>> + TimerMode::Pinned => hrtimer_mode_HRTIMER_MODE_PINNED,
>> + TimerMode::Soft => hrtimer_mode_HRTIMER_MODE_SOFT,
>> + TimerMode::Hard => hrtimer_mode_HRTIMER_MODE_HARD,
>> + TimerMode::AbsolutePinned => hrtimer_mode_HRTIMER_MODE_ABS_PINNED,
>> + TimerMode::RelativePinned => hrtimer_mode_HRTIMER_MODE_REL_PINNED,
>> + TimerMode::AbsoluteSoft => hrtimer_mode_HRTIMER_MODE_ABS_SOFT,
>> + TimerMode::RelativeSoft => hrtimer_mode_HRTIMER_MODE_REL_SOFT,
>> + TimerMode::AbsolutePinnedSoft => hrtimer_mode_HRTIMER_MODE_ABS_PINNED_SOFT,
>> + TimerMode::RelativePinnedSoft => hrtimer_mode_HRTIMER_MODE_REL_PINNED_SOFT,
>> + TimerMode::AbsoluteHard => hrtimer_mode_HRTIMER_MODE_ABS_HARD,
>> + TimerMode::RelativeHard => hrtimer_mode_HRTIMER_MODE_REL_HARD,
>> + TimerMode::AbsolutePinnedHard => hrtimer_mode_HRTIMER_MODE_ABS_PINNED_HARD,
>> + TimerMode::RelativePinnedHard => hrtimer_mode_HRTIMER_MODE_REL_PINNED_HARD,
>> + }
>> + }
>> +}
>
> Are we sure we actually need to explicitly convert it like this? You should be
> able to use #[repr(…)] to indicate that the enum is the same type as the
> actual C constant, and then we can just assign the value of each C constant as
> the discriminant for each enum value in TimerMode.
>
Some combinations of modes are illegal. With this approach, it is not
possible to name the illegal combinations.
Interesting discussion is happening on Zulip regarding a possible
solution for enums like this [1].
Best regards,
Andreas Hindborg
[1] https://rust-for-linux.zulipchat.com/#narrow/channel/291565-Help/topic/Best.20way.20to.20handle.20enum.2Fflags.20situation
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