linux-kernel - Re: [RFC RESEND v10 03/14] irq & spin_lock: Add counted interrupt disabling/enabling

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Message-ID: <703f5e6f-4bfe-4134-ae40-d9d14cd04879@nvidia.com>
Date: Mon, 16 Jun 2025 14:37:49 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Lyude Paul <lyude@...hat.com>,
 rust-for-linux@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
 linux-kernel@...r.kernel.org, Daniel Almeida <daniel.almeida@...labora.com>,
 Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
 David Woodhouse <dwmw@...zon.co.uk>, Jens Axboe <axboe@...nel.dk>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, NeilBrown
 <neilb@...e.de>, Caleb Sander Mateos <csander@...estorage.com>,
 Ryo Takakura <ryotkkr98@...il.com>, K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [RFC RESEND v10 03/14] irq & spin_lock: Add counted interrupt
 disabling/enabling



On 6/16/2025 2:02 PM, Boqun Feng wrote:
> On Mon, Jun 16, 2025 at 01:54:47PM -0400, Joel Fernandes wrote:
> [..]
>>>> Your SOB is placed wrong, should be below Boqun's. This way it gets
>>>> lost.
>>>>
>>>> Also, is there effort planned to fully remove the save/restore variant?
>>>> As before, my main objection is adding variants with overlapping
>>>> functionality while not cleaning up the pre-existing code.
>>>>
>>> My plan is to map local_irq_disable() to local_interrupt_disable() and
>>> keep local_irq_save() as it is. That is, local_irq_disable() is the
>>> auto-pilot version and local_irq_save/restore() is the manual version.
>>> The reason is that I can see more "creative" (i.e. unpaired) usage of
>>> local_irq_save/restore(), and maybe someone would like to keep them.
>>> Thoughts?
>> My thought is it is better to keep them separate at first, let
>> local_interrupt_disable() stabilize with a few users, then convert the
>> callers (possibly with deprecation warnings with checkpatch), and then remove
>> the old API.
>>
> No objection to doing it slowly 😉 My point was more about the plan is
> to replace local_irq_disable() with local_interrupt_disable() other than
> replacing local_irq_save() with local_interrupt_disable().

At first glance that makes sense. Was there some concern about overhead? Me and
Steve did some experiments back in the day where we found local_irq_disable()
can be performance-sensitive, but we were adding tracers/tracing which
presumably can be higher overhead than what this series is doing.

thanks,

 - Hiek