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 5D5ED1A317F; Thu, 6 Feb 2025 14:56:31 +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=1738853792; cv=none; b=BtwWbJir8ow/xC+EaNeQm0m6BdL6P4gEsvAUHfJOVI/4noSCT2I7w1eIwdxB3SF9jXIyrwIKDfrpClTXsFeugkaPrN8XuHJGEzIU5iwyFhDnJq019Tz4r6ceW5M8HUESaHGX5tU+9OzDkeoI10MTBXirA0XjekFDmqaC3nSJqrI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738853792; c=relaxed/simple; bh=5UHJsNjDXs62YUdOMcsq/9tf8PVGSLIq75PwMvF+egA=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=A+mgYUyKJ9b1Rmap0tePqI5gSSF6jF7xktHcwWptJg+meeCFnN2ZmYEDP936ZsguLwVCXtmW3g3zDs6DXDUCjnVRVF2BIU1plTRv8hORR4VL2SuyHoNsSwFRaKUF8T9IkdrMdQlItRO8thHTZoY1WxJmF3USfids3H1Cm02axN0= 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 533F7C4CEDD; Thu, 6 Feb 2025 14:56:28 +0000 (UTC) Date: Thu, 6 Feb 2025 09:57:09 -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: <20250206095709.7a93ac36@gandalf.local.home> In-Reply-To: <20250206142717.GS7145@noisy.programming.kicks-ass.net> References: <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> <20250206142234.-kcSg0xr@linutronix.de> <20250206142717.GS7145@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 15:27:17 +0100 Peter Zijlstra wrote: > I'm assuming you have a recent number around -- what's sane? 5us, less? It really doesn't matter what the number is. No matter what it is, it adds to the latency. Just adding the timer and another interrupt just doubled the interrupt latency. If an RT task were to wake up but this flag is set to extend the currently running task, even if you made it 5us, it will be more than that. You need to enable a new timer, get back to user space, trigger another interrupt, before you can schedule the RT task from its original time it was to wake up and run. -- Steve