linux-kernel - Re: [PATCH v13 3/5] rust: time: Introduce Instant type

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Message-ID: <87lds3cjgx.fsf@kernel.org>
Date: Mon, 14 Apr 2025 09:04:14 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
Cc: "FUJITA Tomonori" <fujita.tomonori@...il.com>,
  <rust-for-linux@...r.kernel.org>,  "Gary Guo" <gary@...yguo.net>,  "Fiona
 Behrens" <me@...enk.dev>,  "Daniel Almeida"
 <daniel.almeida@...labora.com>,  <linux-kernel@...r.kernel.org>,
  <netdev@...r.kernel.org>,  <andrew@...n.ch>,  <hkallweit1@...il.com>,
  <tmgross@...ch.edu>,  <ojeda@...nel.org>,  <alex.gaynor@...il.com>,
  <bjorn3_gh@...tonmail.com>,  <benno.lossin@...ton.me>,
  <a.hindborg@...sung.com>,  <aliceryhl@...gle.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>,
  <tgunders@...hat.com>,  <david.laight.linux@...il.com>
Subject: Re: [PATCH v13 3/5] rust: time: Introduce Instant type

"Boqun Feng" <boqun.feng@...il.com> writes:

> On Sun, Apr 13, 2025 at 07:43:08PM +0900, FUJITA Tomonori 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
>>
>> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
>
> I probably need to drop my Reviewed-by because of something below:
>
>> Reviewed-by: Gary Guo <gary@...yguo.net>
>> Reviewed-by: Fiona Behrens <me@...enk.dev>
>> Tested-by: Daniel Almeida <daniel.almeida@...labora.com>
>> Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
>> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
>> ---
> [...]
>> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
>> index ce53f8579d18..27243eaaf8ed 100644
>> --- a/rust/kernel/time/hrtimer.rs
>> +++ b/rust/kernel/time/hrtimer.rs
>> @@ -68,7 +68,7 @@
>>  //! `start` operation.
>>
>>  use super::ClockId;
>> -use crate::{prelude::*, time::Ktime, types::Opaque};
>> +use crate::{prelude::*, time::Instant, types::Opaque};
>>  use core::marker::PhantomData;
>>  use pin_init::PinInit;
>>
>> @@ -189,7 +189,7 @@ pub trait HrTimerPointer: Sync + Sized {
>>
>>      /// Start the timer with expiry after `expires` time units. If the timer was
>>      /// already running, it is restarted with the new expiry time.
>> -    fn start(self, expires: Ktime) -> Self::TimerHandle;
>> +    fn start(self, expires: Instant) -> Self::TimerHandle;
>
> We should be able to use what I suggested:
>
> 	https://lore.kernel.org/rust-for-linux/Z_ALZsnwN53ZPBrB@boqun-archlinux/
>
> to make different timer modes (rel or abs) choose different expire type.
>
> I don't think we can merge this patch as it is, unfortunately, because
> it doesn't make sense for a relative timer to take an Instant as expires
> value.

I told Tomo he could use `Instant` in this location and either he or I
would fix it up later [1].

I don't want to block the series on this since the new API is not worse
than the old one where Ktime is overloaded for both uses.


Best regards,
Andreas Hindborg



[1] https://lore.kernel.org/all/877c41v7kf.fsf@kernel.org