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

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Message-ID: <20260206084258.GO1282955@noisy.programming.kicks-ass.net>
Date: Fri, 6 Feb 2026 09:42:58 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: Boqun Feng <boqun@...nel.org>, Lyude Paul <lyude@...hat.com>,
	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>
Subject: Re: [PATCH v17 02/16] preempt: Track NMI nesting to separate per-CPU
 counter

On Thu, Feb 05, 2026 at 08:24:40PM -0500, Joel Fernandes wrote:

> > I guess Peter was trying to say it's not a slow path if you consider
> > perf event interrupts on x86? [1]
> 
> How are we handling this performance issue then on 32-bit x86 architecture with
> perf? Or are we saying we don't care about performance on 32-bit?

Yeah, in general I don't consider any 32bit architecture performance
critical at this point. Its pure legacy code, to be removed at some
point.

To x86_32 in particular, we make it limp along. It sorta builds and
sorta boots but meh. It doesn't even have most of the speculation fixes.
You really, as in *REALLY* should not be running a x86_32 kernel.

I mean, if you still want to run Linux on your museum grade Pentium-II
processor, don't let me stop you. Just don't expect miracles.