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From: Peter Zijlstra <peterz@infradead.org>
To: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Lyude Paul <lyude@redhat.com>,
	rust-for-linux@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Boqun Feng <boqun.feng@gmail.com>,
	linux-kernel@vger.kernel.org,
	Daniel Almeida <daniel.almeida@collabora.com>,
	Danilo Krummrich <dakr@kernel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Uladzislau Rezki <urezki@gmail.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	Alex Gaynor <alex.gaynor@gmail.com>, Gary Guo <gary@garyguo.net>,
	Bj??rn Roy Baron <bjorn3_gh@protonmail.com>,
	Benno Lossin <lossin@kernel.org>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Alice Ryhl <aliceryhl@google.com>,
	Trevor Gross <tmgross@umich.edu>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	Ryo Takakura <ryotkkr98@gmail.com>,
	K Prateek Nayak <kprateek.nayak@amd.com>,
	"open list:CPU FREQUENCY SCALING FRAMEWORK"
	<linux-pm@vger.kernel.org>
Subject: Re: [PATCH v13 01/17] preempt: Track NMI nesting to separate per-CPU counter
Date: Tue, 14 Oct 2025 21:37:11 +0200	[thread overview]
Message-ID: <20251014193711.GB1206438@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <c58d01f7-2589-465b-b10e-ba39e01deee1@nvidia.com>

On Tue, Oct 14, 2025 at 01:59:00PM -0400, Joel Fernandes wrote:

> Would that break 32-bit x86? I have to research this more. This was what I
> initially thought of doing but ISTR some challenges. I'd like to think that was
> my imagination, but I will revisit it and see what it takes.

You can do a 64bit addition with 2 instructions on most 32 bit arch,
i386 in specific has: ADD+ADC. Same for many of the other simple ops.
Its multiplication and division where things get tricky, but luckily we
don't do much of those on __preempt_count.

  reply	other threads:[~2025-10-14 19:37 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20251013155205.2004838-1-lyude@redhat.com>
2025-10-13 15:48 ` [PATCH v13 01/17] preempt: Track NMI nesting to separate per-CPU counter Lyude Paul
2025-10-13 16:19   ` Lyude Paul
2025-10-13 16:32     ` Miguel Ojeda
2025-10-13 20:00   ` Peter Zijlstra
2025-10-13 21:27     ` Joel Fernandes
2025-10-14  8:25       ` Peter Zijlstra
2025-10-14 17:59         ` Joel Fernandes
2025-10-14 19:37           ` Peter Zijlstra [this message]
2025-10-14 10:48   ` Peter Zijlstra
2025-10-14 17:55     ` Joel Fernandes
2025-10-14 19:43       ` Peter Zijlstra
2025-10-14 22:05         ` Joel Fernandes
2025-10-20 20:44         ` Joel Fernandes
2025-10-30 22:56           ` Joel Fernandes

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