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

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Message-ID: <20260204130027.GE3016024@noisy.programming.kicks-ass.net>
Date: Wed, 4 Feb 2026 14:00:27 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Gary Guo <gary@...yguo.net>
Cc: 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>,
	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 04, 2026 at 12:32:45PM +0000, Gary Guo wrote:
> 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?

Perf uses NMI. Also, the 64bit code is actually simpler.