linux-kernel - Re: [PATCH v17 02/16] preempt: Track NMI nesting to separate per-CPU counter

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Message-Id: <DG66HSCEA3XP.36DNV6A9HRNOK@garyguo.net>
Date: Wed, 04 Feb 2026 12:32:45 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Peter Zijlstra" <peterz@...radead.org>, "Lyude Paul" <lyude@...hat.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 "Thomas Gleixner" <tglx@...utronix.de>, "Boqun Feng"
 <boqun.feng@...il.com>, "Daniel Almeida" <daniel.almeida@...labora.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>,
 "Andrew Morton" <akpm@...ux-foundation.org>, "Ingo Molnar"
 <mingo@...hat.com>, "Will Deacon" <will@...nel.org>, "Waiman Long"
 <longman@...hat.com>, "Joel Fernandes" <joelagnelf@...dia.com>
Subject: Re: [PATCH v17 02/16] preempt: Track NMI nesting to separate
 per-CPU counter

On Wed Feb 4, 2026 at 11:12 AM GMT, Peter Zijlstra wrote:
> On Tue, Feb 03, 2026 at 01:15:21PM +0100, Peter Zijlstra wrote:
>> But I'm really somewhat sad that 64bit can't do better than this.
>
> Here, the below builds and boots (albeit with warnings because printf
> format crap sucks).

Hi Peter,

I am not sure if it's worth the complexity to do this for the NMI code path.
I don't think NMI code path is hot enough that this is necessary?

Best,
Gary

>
> ---
>  arch/x86/Kconfig               |  1 +
>  arch/x86/include/asm/preempt.h | 53 ++++++++++++++++++++++++++++++------------
>  arch/x86/kernel/cpu/common.c   |  2 +-
>  include/linux/hardirq.h        |  7 +++---
>  include/linux/preempt.h        | 52 ++++++++++++++++++++++++++++++++++-------
>  init/main.c                    |  2 +-
>  kernel/Kconfig.preempt         |  4 ++++
>  kernel/sched/core.c            |  8 +++----
>  kernel/softirq.c               | 10 +++++++-
>  kernel/time/timer.c            |  2 +-
>  lib/locking-selftest.c         |  2 +-
>  11 files changed, 106 insertions(+), 37 deletions(-)