From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 865C4C0219B for ; Tue, 11 Feb 2025 15:30:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0A3656B008C; Tue, 11 Feb 2025 10:30:54 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0541D6B0092; Tue, 11 Feb 2025 10:30:54 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E5EE86B0093; Tue, 11 Feb 2025 10:30:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id C5F5C6B008C for ; Tue, 11 Feb 2025 10:30:53 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 9AC5FC058A for ; Tue, 11 Feb 2025 15:28:02 +0000 (UTC) X-FDA: 83108044446.03.4A063F5 Received: from nyc.source.kernel.org (nyc.source.kernel.org [147.75.193.91]) by imf16.hostedemail.com (Postfix) with ESMTP id F26D6180012 for ; Tue, 11 Feb 2025 15:28:00 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf16.hostedemail.com: domain of "SRS0=6phq=VC=goodmis.org=rostedt@kernel.org" designates 147.75.193.91 as permitted sender) smtp.mailfrom="SRS0=6phq=VC=goodmis.org=rostedt@kernel.org" ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1739287681; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qqbfA9auZAq67fysheKMMoUR5ij83rlbzAtLZgsazho=; b=beOv5MQr3qjuFus9h5RaObROdQyQ+ICdSaOyXJqo52y12RbDb9QcTLq7kasCk3K/iJRghX 6CEZcaHy2sOO4zBCnyolOOLsYA/TxwzGN88PBiQovu994S7gxlCZyG4j3fT8l1G4VDKTSc XivS/hPZ7VuM3AqdCn1fBiE1qMf+V0U= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf16.hostedemail.com: domain of "SRS0=6phq=VC=goodmis.org=rostedt@kernel.org" designates 147.75.193.91 as permitted sender) smtp.mailfrom="SRS0=6phq=VC=goodmis.org=rostedt@kernel.org" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1739287681; a=rsa-sha256; cv=none; b=HVo9SnEc0eWefZroQQC9+sgkdu+KZ4SQIqbec4WyiVjG2ijtvz39HASJ8skm8a7Zy8ANN7 SYztuncearGXIl2ANxP7BtvLciu3pFGdNqfDGPkyJWypTfYsz3FHii5gyWw3XwoFl79PBy XE/A7wly53flFifkn4NSckDMbEIbdvY= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id C3601A407C3; Tue, 11 Feb 2025 15:26:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 650FAC4CEDD; Tue, 11 Feb 2025 15:27:56 +0000 (UTC) Date: Tue, 11 Feb 2025 10:28:01 -0500 From: Steven Rostedt To: Sebastian Andrzej Siewior Cc: Joel Fernandes , Prakash Sangappa , Peter Zijlstra , 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: <20250211102801.5b32d610@gandalf.local.home> In-Reply-To: <20250211082138.iqvedSfG@linutronix.de> 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> <20250210144321.1f5974a6@gandalf.local.home> <20250211082138.iqvedSfG@linutronix.de> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: F26D6180012 X-Stat-Signature: iwcsjo154w9ueoz1hi7b3e5wis8bxbkm X-HE-Tag: 1739287680-3758 X-HE-Meta: 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 MkQT7ydk hopGjtvIip8hzFb/ShPAFKW98N4inWK3iHUF4Opf9kSM83fWfTrDUw2Krl9zkMxsJJ5IgtNOxPer2hMYk4PHQ7AfWfWPHndi6GlLHs66SWNZDuyrQfRuhgbzrIH2tzBqexBbnSpopgRl7adYICorIL+Y2CM0nW7CxiKRU2UCB41afxPFQNhLTmLZuH22g9L+rV7Onldyta3h1sOgTI9mxn+Hdo/4jPPVZUEKk7gPBzOT0eZwo59yWG9u62Wi4iO6ifLWiRSmQBTqV9nYGiUlIL7eEv3XcjDeva+7xlblbh9jUhmSB3/3GsDEvgCNQAs6rvyCa X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 11 Feb 2025 09:21:38 +0100 Sebastian Andrzej Siewior wrote: > We don't follow this behaviour exactly today. > > Adding this behaviour back vs the behaviour we have now, doesn't seem to > improve anything at visible levels. We don't have a counter but we can > look at the RCU nesting counter which should be zero once locks have > been dropped. So this can be used for testing. > > But as I said: using "run to completion" and preempt on the return > userland rather than once the lazy flag is seen and all locks have been > released appears to be better. > > It is (now) possible that you run for a long time and get preempted > while holding a spinlock_t. It is however more likely that you release > all locks and get preempted while returning to userland. IIUC, today, LAZY causes all SCHED_OTHER tasks to act more like PREEMPT_NONE. Is that correct? Now that the PREEMPT_RT is not one of the preemption selections, when you select PREEMPT_RT, you can pick between CONFIG_PREEMPT and CONFIG_PREEMPT_LAZY. Where CONFIG_PREEMPT will preempt the kernel at the scheduler tick if preemption is enabled and CONFIG_PREEMPT_LAZY will not preempt the kernel on a scheduler tick and wait for exit to user space. Sebastian, It appears you only tested the CONFIG_PREEMPT_LAZY selection. Have you tested the difference of how CONFIG_PREEMPT behaves between PREEMPT_RT and no PREEMPT_RT? I think that will show a difference like we had in the past. I can see people picking both PREEMPT_RT and CONFIG_PREEMPT (Full), but then wondering why their non RT tasks are suffering from a performance penalty from that. -- Steve