linux-kernel - Re: [RFC PATCH v1] stop_machine: Add stop_housekeeping

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Message-ID: <CADDUTFy_50LR97ZgE=9TduSK0nHwYy+OxjAdA_-Fy+zANT_m-g@mail.gmail.com>
Date: Mon, 6 Jan 2025 15:08:11 +0200
From: Costa Shulyupin <costa.shul@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: Re: [RFC PATCH v1] stop_machine: Add stop_housekeeping_cpuslocked()

On Wed, 18 Dec 2024 at 19:38, Frederic Weisbecker <frederic@...nel.org> wrote:
> And so given the cost of such analysis and resulting possible patches, here
> is an important question: is it worth the effort? What is the usecase of
> shutting down a CPU while other isolated CPUs run critical isolated stuff?

The goal is to implement dynamic CPU isolation for realtime tasks such as DPDK.

Thomas Gleixner in https://lore.kernel.org/lkml/87bjz2210r.ffs@tglx/ suggested:
"CPU hotplug solves this problem without any hackery. Take a CPU offline,
change the mask of that CPU and bring it online again. Repeat until all
CPU changes are done."

Unfortunately, CPU HP interferes with realtime tests and is
unsuitable for dynamic CPU isolation.

Meanwhile, the maximum number of hyperthreads is climbing to 1024,
increasing the demand for CPU HP.

Thank you,
Costa