From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD1421C701B; Thu, 6 Feb 2025 14:20:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738851604; cv=none; b=K0anJOdB3P/0SUk0ra5CG3tJmEYCMSFHaHvxpEMWGV04gH1GYbxe7FtBm/pK7tTmySUQyt2LssLamx/vqaPJFQrHZlVrN0DVx/Mp82f4gtilBf1/LW71bpI38DH51Lw6vZE7iJPnkRIpsSGB/zmZXDkzz6Rxz1oqMsAJzDe8VZg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738851604; c=relaxed/simple; bh=8zhiOVMWM2UTqpclKsMYw9zAEMLFGiqSBOPssYpwBi8=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Vwp3c6mzvyeKxULOLFJKKMYH/1zskysoTiSGZ1fPmICQAYdWl2hZToGyPAyLuJndzCSR87WgPIJ4g7EH7/FhUyaSRhLJoiWyqbK3otNN5+3nagJhJEi/Fd7Lg5GPJV3NwWGnLdzKqKEBxwhB3yyd1rtv9xn/Uydxx2fUK1eQ89g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90427C4CEE2; Thu, 6 Feb 2025 14:20:00 +0000 (UTC) Date: Thu, 6 Feb 2025 09:20:41 -0500 From: Steven Rostedt To: Peter Zijlstra Cc: Sebastian Andrzej Siewior , Joel Fernandes , Prakash Sangappa , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Thomas Gleixner , Ankur Arora , Linus Torvalds , linux-mm@kvack.org, x86@kernel.org, Andrew Morton , luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, Boris Ostrovsky , Konrad Wilk , jgross@suse.com, Andrew.Cooper3@citrix.com, Vineeth Pillai , Suleiman Souhlal , Ingo Molnar , Mathieu Desnoyers , Clark Williams , daniel.wagner@suse.com, Joseph Salisbury , broonie@gmail.com Subject: Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice Message-ID: <20250206092041.3fe52ff5@gandalf.local.home> In-Reply-To: <20250206135744.GQ7145@noisy.programming.kicks-ass.net> References: <9DA1FAE6-A008-4785-BDF9-541457E29807@joelfernandes.org> <20250204220418.35949317@gandalf.local.home> <20250205081635.397eacb0@gandalf.local.home> <20250206083039.0916ad24@gandalf.local.home> <20250206134408.lD_POjuG@linutronix.de> <20250206134859.GP7145@noisy.programming.kicks-ass.net> <20250206135353.i1tp4vDv@linutronix.de> <20250206135744.GQ7145@noisy.programming.kicks-ass.net> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 6 Feb 2025 14:57:44 +0100 Peter Zijlstra wrote: > Right, but so what? Same delay will happen if interrupt fires in the > middle of a preempt_disable() region. > > Or if interrupt gets pending while interrupts are disabled, except your > trace will not show that. > > Your worst case response time isn't affected. That's all that matters. So now if a task has this set, and an interrupt goes off and wakes an RT task, not only is the time of the interrupt the latency of the RT task, but also this extension of the SCHED_OTHER task. That is, where it use to be: event RT task scheduled | | v v time: |-------+-+----+-- ^ | interrupt If the interrupt triggered just as the task set this bit, we then have: event set Xus RT task scheduled | | | v v v time: |-------+-+----+-------+--+ ^ ^ | | interrupt Xus timer triggered This adds on *top* of the current latency, and is not just by itself. Yes, this may not happen often, but in RT we very much do care about the worst case scenarios. (That's the difference between an RT project and a project that just uses RT). -- Steve