From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 B6E2622577F; Thu, 6 Feb 2025 14:27:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738852058; cv=none; b=U6/DELhzG6+Bo99i59OkGYnNSvekcMs2BtCNELNls7ZWw8ddKkvrMHCPlbWKvsKTyzRQuLWw+IwGQoCgmQ9Sky4l9BDfoYD4cBL6qH1alHa3DoGcsPvprUBprcYJpbCfNVPwa9HyvWeeYb25Y4gPAc8pBo+j8OQm9GE0g3Z0U70= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738852058; c=relaxed/simple; bh=BezN76/8VPt9jHagI6jVcVKYjsqhc56dWOvbCZY7qQQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eqyl0dc1eOZDiXc10WyemHCL1LUxAzIO5r7fCmoDrBum30d4fu3QKVtNqGCCWqpZHDf7C1LQyLom1/BRSPLwa6KlaobjkMHICLGrlMK11w4gK49EObeyqUYwuQm0In9/ksghrK6l8z0yuXzIhoP7TJUrMv8yK1YG8yNWstXnTwE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=r/sXPZbY; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="r/sXPZbY" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=aHjwizHLsq1lp0fJhwaBPxokex1B77SgmxhHOi1t7L4=; b=r/sXPZbYGcHJakUNZ5H8VPoe8J 5t+SagAgodvqNeWJRNs61iA7b5jFFhQR6nvR6jI2szVVsvdl17Kt4HNUy/TTbDYQuwLwo9YaeF0Rl kXU5rbHE+BjzmQ+zZXrvj4/+tgbxyqeZn3BchWXCTjtFa+5QkSPY3cX/IuT4Cdg9QJ8ZKd/wkRb2L RT1S/LWVPiThEL9JUU+fgXykigzgHuuw1yldZBRp0abuKDxXxcwoacNCAuV76ChhVz/txX7RBEJgo +Te0w0e0+MNi7kxnqjk/PTt5BFfACddZiyadZed8Tt5l0wY2fiQ2MIbgH5u8V13OEmfQrb1myD/bj IjWlru7Q==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tg2qb-000000067kn-3VUi; Thu, 06 Feb 2025 14:27:17 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 6802E30050D; Thu, 6 Feb 2025 15:27:17 +0100 (CET) Date: Thu, 6 Feb 2025 15:27:17 +0100 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: Steven Rostedt , 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: <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> 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-Disposition: inline In-Reply-To: <20250206142234.-kcSg0xr@linutronix.de> On Thu, Feb 06, 2025 at 03:22:34PM +0100, Sebastian Andrzej Siewior wrote: > Then this feature adds 20us on top? The point has always been for the number to be < the observable scheduling latency. I'm not sure what that number is, and it is always hardware dependent. I measured it on a random test box when I did the prototype a long while ago, and ended up at 50us, but for all I know that machine was running a lockdep enabled kernel at the time (won't be the first and certainly won't be the last time I try and do a performance measurement on a debug kernel). That was not the important part -- but everybody fixates on the number, instead of the intent. I'm assuming you have a recent number around -- what's sane? 5us, less?