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Wyatt IV" To: Gabriele Monaco Cc: linux-kernel@vger.kernel.org, Anna-Maria Behnsen , Thomas Gleixner , Waiman Long , Tejun Heo , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , cgroups@vger.kernel.org, "John B. Wyatt IV" Subject: Re: [PATCH v12 9/9] timers: Exclude isolated cpus from timer migration Message-ID: References: <20250915145920.140180-11-gmonaco@redhat.com> <20250915145920.140180-20-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250915145920.140180-20-gmonaco@redhat.com> On Mon, Sep 15, 2025 at 04:59:30PM +0200, Gabriele Monaco wrote: Your patchset continues to pass when applied against v6.17-rc4-rt3 on a preview of RHEL 10.2. rtla osnoise top -c 1 -e sched:sched_switch -s 20 -T 1 -t -d 30m -q duration: 0 00:30:00 | time is in us CPU Period Runtime Noise % CPU Aval Max Noise Max Single HW NMI IRQ Softirq Thread 1 #1799 1799000001 3351316 99.81371 2336 9 400 0 1799011 0 23795 > This effect was noticed on a 128 cores machine running oslat on the > isolated cores (1-31,33-63,65-95,97-127). The tool monopolises CPUs, > and the CPU with lowest count in a timer migration hierarchy (here 1 > and 65) appears as always active and continuously pulls global timers, > from the housekeeping CPUs. This ends up moving driver work (e.g. > delayed work) to isolated CPUs and causes latency spikes: > If you do another version; you may want to amend the cover letter to include this affect can be noticed with a machine with as few as 20cores/40threads with isocpus set to: 1-9,11-39 with rtla-osnoise-top Tested-by: John B. Wyatt IV Tested-by: John B. Wyatt IV -- Sincerely, John Wyatt Software Engineer, Core Kernel Red Hat