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charset=utf-8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\)) Subject: Re: [PATCH v1 2/2] rust: Add read_poll_timeout_atomic function From: Daniel Almeida In-Reply-To: Date: Tue, 26 Aug 2025 13:59:46 -0300 Cc: FUJITA Tomonori , a.hindborg@kernel.org, alex.gaynor@gmail.com, ojeda@kernel.org, aliceryhl@google.com, anna-maria@linutronix.de, bjorn3_gh@protonmail.com, boqun.feng@gmail.com, frederic@kernel.org, gary@garyguo.net, jstultz@google.com, linux-kernel@vger.kernel.org, lossin@kernel.org, lyude@redhat.com, rust-for-linux@vger.kernel.org, sboyd@kernel.org, tglx@linutronix.de, tmgross@umich.edu, acourbot@nvidia.com Content-Transfer-Encoding: quoted-printable Message-Id: <33725E09-3994-4306-AD4F-4A0253261DE1@collabora.com> References: <20250821035710.3692455-1-fujita.tomonori@gmail.com> <20250821035710.3692455-3-fujita.tomonori@gmail.com> To: Danilo Krummrich X-Mailer: Apple Mail (2.3826.700.81) X-ZohoMailClient: External > On 26 Aug 2025, at 11:12, Danilo Krummrich wrote: >=20 > On Thu Aug 21, 2025 at 5:57 AM CEST, FUJITA Tomonori wrote: >> +pub fn read_poll_timeout_atomic( >> + mut op: Op, >> + mut cond: Cond, >> + delay_delta: Delta, >> + timeout_delta: Delta, >> +) -> Result >> +where >> + Op: FnMut() -> Result, >> + Cond: FnMut(&T) -> bool, >> +{ >> + let mut left_ns =3D timeout_delta.as_nanos(); >> + let delay_ns =3D delay_delta.as_nanos(); >> + >> + loop { >> + let val =3D op()?; >> + if cond(&val) { >> + // Unlike the C version, we immediately return. >> + // We know the condition is met so we don't need to = check again. >> + return Ok(val); >> + } >> + >> + if left_ns < 0 { >> + // Unlike the C version, we immediately return. >> + // We have just called `op()` so we don't need to call = it again. >> + return Err(ETIMEDOUT); >> + } >> + >> + if !delay_delta.is_zero() { >> + udelay(delay_delta); >> + left_ns -=3D delay_ns; >> + } >> + >> + cpu_relax(); >> + left_ns -=3D 1; >=20 > How do we know that each iteration costs 1ns? To make it even more = obvious, we > don't control the implementation of cond(). Shouldn't we use ktime for = this? I don=E2=80=99t think ktime can be used from an atomic context? =E2=80=94 Daniel