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 0CF7CC4167D for ; Wed, 8 Nov 2023 16:22:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6F5218001F; Wed, 8 Nov 2023 11:22:31 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6A4C28D0073; Wed, 8 Nov 2023 11:22:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 593848001F; Wed, 8 Nov 2023 11:22:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 499748D0073 for ; Wed, 8 Nov 2023 11:22:31 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 227F7B5F86 for ; Wed, 8 Nov 2023 16:22:31 +0000 (UTC) X-FDA: 81435304902.02.8E1F811 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf24.hostedemail.com (Postfix) with ESMTP id 6B200180014 for ; Wed, 8 Nov 2023 16:22:29 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=none; spf=pass (imf24.hostedemail.com: domain of "SRS0=kuE6=GV=goodmis.org=rostedt@kernel.org" designates 139.178.84.217 as permitted sender) smtp.mailfrom="SRS0=kuE6=GV=goodmis.org=rostedt@kernel.org"; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1699460549; 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=AWK7F7ktH4yHp95lDLz0hqsekdY8ZekFpyRo3UMHRxk=; b=a/HSXuWMein5q+Pcpl2+vGqU7SJ54sbrl26dFhkDOygOH+DYsD9qN/jIzAqzI0M5xaa1gR DxBD7NvLtVFj0Ul4s4YrlT+FF329SRmHX3OUde1CKbQMMMi/q2kBWid7+vNsKxMozM0QUd EMu85BkJ6Cxo0IWwq8ooz5JFV3IN4cE= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1699460549; a=rsa-sha256; cv=none; b=I44547C/ZdtpQGldPfDqJWMS8oAV2qn6b4smSr09Rc8s6/9hn53qsq5QzrKmCbGUZHIMBd RPWX05+wXdNe9YjqemX2+JzXKdSFnEALV+0mGnk6dDtCjnOuWBvxlCUzr7CaWg8Ur59QvI 8NjrXI2bRyidFLLVKTnpAG71CNOk9os= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none; spf=pass (imf24.hostedemail.com: domain of "SRS0=kuE6=GV=goodmis.org=rostedt@kernel.org" designates 139.178.84.217 as permitted sender) smtp.mailfrom="SRS0=kuE6=GV=goodmis.org=rostedt@kernel.org"; dmarc=none Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 1C8B6614EC; Wed, 8 Nov 2023 16:22:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2548FC433C8; Wed, 8 Nov 2023 16:22:24 +0000 (UTC) Date: Wed, 8 Nov 2023 11:22:27 -0500 From: Steven Rostedt To: Thomas Gleixner Cc: Peter Zijlstra , Ankur Arora , linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, paulmck@kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.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@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, mingo@kernel.org, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com Subject: Re: [RFC PATCH 00/86] Make the kernel preemptible Message-ID: <20231108112227.62f0c5a8@gandalf.local.home> In-Reply-To: <877cmsgsrg.ffs@tglx> References: <20231107215742.363031-1-ankur.a.arora@oracle.com> <20231108085156.GD8262@noisy.programming.kicks-ass.net> <87bkc4lfxp.fsf@oracle.com> <20231108101330.GK3818@noisy.programming.kicks-ass.net> <877cmsgsrg.ffs@tglx> X-Mailer: Claws Mail 3.19.1 (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-Stat-Signature: iui8duji3c6bq8jdatzcozpgyud4eihg X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6B200180014 X-Rspam-User: X-HE-Tag: 1699460549-196706 X-HE-Meta: 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 QAIh/Vtp j28N0oVmgh8E2QKSLSqKrnf/1g49Vjzvt0jzqDVDJaf1xMuWDDuuGSHr99a1gSO4KfjF1QXrrx8DPZ5sFfraFqGBfqlfKJqmUfJz0hfaI5psQ13+Bq/4oDtVBY/7KJqq9/LrXdbfNCGnMRbtHA5cWzPODsizTDwHarfTew0t6vKI3Fo0Ve7uQqZ+BvbHbc70so6iM5CTQ3vRKUvgWst5UzsCoGj17S3+LVtFR2JtXakyPAPdhiz7tWHNJs/6n4LdXW9oyTwOX9rAuevupAJleQfFhP9xjS68UNPUqQLTkftbeqlsM0gaIXxYORg== 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 Wed, 08 Nov 2023 16:38:11 +0100 Thomas Gleixner wrote: > On Wed, Nov 08 2023 at 11:13, Peter Zijlstra wrote: > > On Wed, Nov 08, 2023 at 02:04:02AM -0800, Ankur Arora wrote: > > I'm not understanding, those should stay obviously. > > > > The current preempt_dynamic stuff has 5 toggles: > > > > /* > > * SC:cond_resched > > * SC:might_resched > > * SC:preempt_schedule > > * SC:preempt_schedule_notrace > > * SC:irqentry_exit_cond_resched > > * > > * > > * NONE: > > * cond_resched <- __cond_resched > > * might_resched <- RET0 > > * preempt_schedule <- NOP > > * preempt_schedule_notrace <- NOP > > * irqentry_exit_cond_resched <- NOP > > * > > * VOLUNTARY: > > * cond_resched <- __cond_resched > > * might_resched <- __cond_resched > > * preempt_schedule <- NOP > > * preempt_schedule_notrace <- NOP > > * irqentry_exit_cond_resched <- NOP > > * > > * FULL: > > * cond_resched <- RET0 > > * might_resched <- RET0 > > * preempt_schedule <- preempt_schedule > > * preempt_schedule_notrace <- preempt_schedule_notrace > > * irqentry_exit_cond_resched <- irqentry_exit_cond_resched > > */ > > > > If you kill voluntary as we know it today, you can remove cond_resched > > and might_resched, but the remaining 3 are still needed to switch > > between NONE and FULL. > > No. The whole point of LAZY is to keep preempt_schedule(), > preempt_schedule_notrace(), irqentry_exit_cond_resched() always enabled. Right. * NONE: * cond_resched <- __cond_resched * might_resched <- RET0 * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP Peter, how can you say we can get rid of cond_resched() in NONE when you show that NONE still uses it? I thought the entire point of this was to get rid of all the cond_resched() and they are there for PREEMPT_NONE as well as VOLUNTARY. As you showed above, the only difference between NONE and VOLUNTARY was the might_sleep. > > Look at my PoC: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/ And I've been saying that many times already ;-) Thanks Thomas for reiterating it. -- Steve