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Fri, 30 May 2025 08:00:33 -0700 (PDT) MIME-Version: 1.0 References: <93e83ed5-bcf3-4a5e-b713-4f9612ff7a6d@efficios.com> In-Reply-To: <93e83ed5-bcf3-4a5e-b713-4f9612ff7a6d@efficios.com> Date: Fri, 30 May 2025 16:00:23 +0100 X-Gm-Features: AX0GCFsCqZPn0wD19btFcuUJvqFbqOy72kp-BPzIVHnG-QNLvH6z3A8F26mvAHo Message-ID: Subject: Re: A question regarding isolated cpus and software interrupts To: Mathieu Desnoyers Cc: lttng-dev@lists.lttng.org, Frederic Weisbecker Content-Type: text/plain; charset="UTF-8" X-Mailman-Approved-At: Fri, 30 May 2025 11:02:32 -0400 X-BeenThere: lttng-dev@lists.lttng.org X-Mailman-Version: 2.1.39 Precedence: list List-Id: LTTng development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: David Aldrich via lttng-dev Reply-To: David Aldrich Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" Hi Mathieu Thanks for your reply. > How are the cores isolated on your system (exact kernel command line > options or commands issued) ? There are various degree of fine-tuning > to prevent disturbance from the tick (nohz full), scheduling, and > irqs that can be done explicitly. So depending on your specific > configuration, you may be missing isolation options that would > prevent the softirq from running on your isolated cpus. Our kernel parameters are: ro skew_tick=1 rcu_nocb_poll rcu_nocbs=4-31 nohz=on nohz_full=4-31 kthread_cpus=0-3 irqaffinity=0-3 isolcpus=managed_irq,domain,4-31 intel_pstate=passive nosoftlockup tsc=nowatchdog intel_iommu=on iommu=pt default_hugepagesz=1G hugepagesz=1G hugepages=4 vfio_pci.enable_sriov=1 vfio_pci.disable_idle_d3=1 (the affected thread runs on core 4). Best regards David