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 65F35C61D97 for ; Tue, 21 Nov 2023 22:52:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9B22A6B04F7; Tue, 21 Nov 2023 17:52:06 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 961D66B04FC; Tue, 21 Nov 2023 17:52:06 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 851806B0517; Tue, 21 Nov 2023 17:52:06 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 7559D6B04F7 for ; Tue, 21 Nov 2023 17:52:06 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 4FC23160A98 for ; Tue, 21 Nov 2023 22:52:06 +0000 (UTC) X-FDA: 81483461052.03.1DA91DE Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by imf15.hostedemail.com (Postfix) with ESMTP id ED59AA001B for ; Tue, 21 Nov 2023 22:52:03 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of "SRS0=YbhT=HC=goodmis.org=rostedt@kernel.org" designates 145.40.73.55 as permitted sender) smtp.mailfrom="SRS0=YbhT=HC=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=1700607124; 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=iNB+5XOZr3a3B6lMqiZCI2YyTYheSN+3jsAFYVitQaQ=; b=CzuhsPoTVAdEwnlu5UuuPbcPTVYKcc6odlUJdiBw3ch31vJxLiiy9g9Plw3y4bsPK83DPo JQpFqPUN/NcKnMZ8+YYT7qeyXHcb52wM+nhejcicPiFdPl0C3KJbFG88PCH5bapaWonl+H 9MV/kETrtaZmWzOLQ+4ayuCv7VTwAHE= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of "SRS0=YbhT=HC=goodmis.org=rostedt@kernel.org" designates 145.40.73.55 as permitted sender) smtp.mailfrom="SRS0=YbhT=HC=goodmis.org=rostedt@kernel.org"; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1700607124; a=rsa-sha256; cv=none; b=FOrGFpdEWbcWC9BkDzHXFJufjaYUVIANFtoqVUasCYn7zwCoh3PInH0Tl+JfjArfH5U4SH RX4qjgHGcZHb6CNOHSOlPIxovZRF8uiUqwqdsn/q/7W22ylMXp2htCqCDTokdSI6C7rTdf tgU+fyM2PTrcmw0s/b7WE6TC7pI34l8= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id ACC87CE1E13; Tue, 21 Nov 2023 22:51:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5F5FAC433C8; Tue, 21 Nov 2023 22:51:55 +0000 (UTC) Date: Tue, 21 Nov 2023 17:52:09 -0500 From: Steven Rostedt To: "Paul E. McKenney" Cc: Peter Zijlstra , Ankur Arora , linux-kernel@vger.kernel.org, tglx@linutronix.de, torvalds@linux-foundation.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 48/86] rcu: handle quiescent states for PREEMPT_RCU=n Message-ID: <20231121175209.1d7ec202@gandalf.local.home> In-Reply-To: <4605b4f4-8a2b-4653-b684-9c696c36ebd0@paulmck-laptop> References: <20231107215742.363031-1-ankur.a.arora@oracle.com> <20231107215742.363031-49-ankur.a.arora@oracle.com> <2027da00-273d-41cf-b9e7-460776181083@paulmck-laptop> <87lear4wj6.fsf@oracle.com> <46a4c47a-ba1c-4776-a6f8-6c2146cbdd0d@paulmck-laptop> <31d50051-e42c-4ef2-a1ac-e45370c3752e@paulmck-laptop> <20231121203049.GN8262@noisy.programming.kicks-ass.net> <1cdbb0f6-9078-4023-bf37-8d826ca0c711@paulmck-laptop> <20231121163834.571abb52@gandalf.local.home> <4605b4f4-8a2b-4653-b684-9c696c36ebd0@paulmck-laptop> 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-Rspamd-Queue-Id: ED59AA001B X-Rspam-User: X-Stat-Signature: bmb8ij1x6wo6is5xi5gcr7z6z8kopqdd X-Rspamd-Server: rspam01 X-HE-Tag: 1700607123-642116 X-HE-Meta: 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 udPdqcYK Nyw2OxDa6beqHzVCUFpPWQPsIyKkIcB4HUktpzDDu7NPnoaRBarDc8HXxUbPk9yk2MbRIsBJ+cs6yuIvaRCFU/SaQRsvxqfYFBuHnRCT65NfaFWq9dg/ubHJa2+MBTCZ9kz6Qn3PgtFdsZwFV1RexbuvVzE4Ob9RLbK14VOFjNgFiAaQppNa54tcUmtRQFWi7g1qamLuU7YEfPWsWQwomhLIaHwgywmLB1Y0nrubeHtrwxlwKpFdGbGVDkRPQJVMuzzAy9qzZSJ2Z7a4GLkrH7U3x1QahjEejGQpR07/uiTa1IZE7+58MfyiT/mHywQziXlpps6acH9QOPIxgcYZWXa0qwqtEjIa3BLztlmR0unR8txo= 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, 21 Nov 2023 14:26:33 -0800 "Paul E. McKenney" wrote: > On Tue, Nov 21, 2023 at 04:38:34PM -0500, Steven Rostedt wrote: > > On Tue, 21 Nov 2023 13:14:16 -0800 > > "Paul E. McKenney" wrote: > > > > > On Tue, Nov 21, 2023 at 09:30:49PM +0100, Peter Zijlstra wrote: > > > > On Tue, Nov 21, 2023 at 11:25:18AM -0800, Paul E. McKenney wrote: > > > > > #define preempt_enable() \ > > > > > do { \ > > > > > barrier(); \ > > > > > if (!IS_ENABLED(CONFIG_PREEMPT_RCU) && raw_cpu_read(rcu_data.rcu_urgent_qs) && \ > > > > > (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK | HARDIRQ_MASK | NMI_MASK) == PREEMPT_OFFSET) && > > > > > !irqs_disabled()) \ > > > > Could we make the above an else case of the below if ? > > Wouldn't that cause the above preempt_count() test to always fail? preempt_count_dec_and_test() returns true if preempt_count() is zero, which happens only if NEED_RESCHED is set, and the rest of preempt_count() is not set. (NEED_RESCHED bit in preempt_count() is really the inverse of NEED_RESCHED). Do we need to call rcu_all_qs() when we call the scheduler? Isn't scheduling a quiescent state for most RCU flavors? I thought this was to help move along the quiescent states without added cond_resched() around, which has: int __sched __cond_resched(void) { if (should_resched(0)) { preempt_schedule_common(); return 1; } /* * In preemptible kernels, ->rcu_read_lock_nesting tells the tick * whether the current CPU is in an RCU read-side critical section, * so the tick can report quiescent states even for CPUs looping * in kernel context. In contrast, in non-preemptible kernels, * RCU readers leave no in-memory hints, which means that CPU-bound * processes executing in kernel context might never report an * RCU quiescent state. Therefore, the following code causes * cond_resched() to report a quiescent state, but only when RCU * is in urgent need of one. */ #ifndef CONFIG_PREEMPT_RCU rcu_all_qs(); #endif return 0; } Where if we schedule, we don't call rcu_all_qs(). I stand by that being in the else statement. It looks like that would keep the previous work flow. -- Steve