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Fri, 09 May 2025 09:00:29 -0700 (PDT) MIME-Version: 1.0 Date: Fri, 9 May 2025 17:00:17 +0100 X-Gm-Features: AX0GCFs2qvXEm2I1fz6hUQ4wIpnEmwztq1SjP4_ZJhOyxh3mHqiJiH4kkkWk4KU Message-ID: Subject: Understanding SOFT IRQ 1 To: lttng-dev@lists.lttng.org Content-Type: text/plain; charset="UTF-8" X-Mailman-Approved-At: Fri, 09 May 2025 12:11:09 -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 I am just getting started with LTTng and Trace Compass. I can capture Kernel and UST events. My purpose is to investigate why a periodic task, running on an isolated core, has occasional blips i.e. it's period (duration) extends. I have inserted tracepoints to mark normal and extended durations. In Trace Compass the blip tracepoint is preceded by a brown state that is 'SOFT IRQ 1'. This extends down all cores. It lasts 105us and is likely to be the reason for the blip. Please could someone explain to me what may be happening here and how can I find out the reason for this SOFT IRQ? Best regards David