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 X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2FC4DC4320A for ; Wed, 28 Jul 2021 18:23:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0FC0C6101C for ; Wed, 28 Jul 2021 18:23:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229719AbhG1SXJ (ORCPT ); Wed, 28 Jul 2021 14:23:09 -0400 Received: from mail.efficios.com ([167.114.26.124]:39326 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229542AbhG1SXI (ORCPT ); Wed, 28 Jul 2021 14:23:08 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id AE39735A877; Wed, 28 Jul 2021 14:23:06 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id NAP0lL2hjJ48; Wed, 28 Jul 2021 14:23:06 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id EE3F335A876; Wed, 28 Jul 2021 14:23:05 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com EE3F335A876 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1627496586; bh=hauLVrEgwWpB0ANJV3qETO85yNuqLONWAWa6VN6nqvY=; h=Date:From:To:Message-ID:MIME-Version; b=SEA18qDI1plWvATxaKsAHGsLukzrHFz6m2RxvH05mLRSpq+l6EtVPTB0iy02t/EX/ a5kVzQv6Dh0yLcQTZXMFyGx/6aobYxv5W4tr9h9hSQSSeZJvzno6pAgP2u/1297gG5 OoWCgWi5CdkEw/sF31eXjVQVVJ4zdp6NMla+zoWNgXSn9rvWcdcCZhief/jGOwed8M QeTUJ7GDjmQa6KiXQ2X0ds+8NdMjnoDBmjpR4wtvv3UhCjXcikRv/eqh2HCZkWSB76 uFIzatOvEni/7GzQEFucOVYtG4WBvJ2OnIejTjYKIBP+utqJDIFupIfDJ9LD77va1J OsHuZqjOop9EA== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id hG9UPV3k96T0; Wed, 28 Jul 2021 14:23:05 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id D84B935A875; Wed, 28 Jul 2021 14:23:05 -0400 (EDT) Date: Wed, 28 Jul 2021 14:23:05 -0400 (EDT) From: Mathieu Desnoyers To: paulmck Cc: rcu , linux-kernel , kernel-team , Ingo Molnar , Lai Jiangshan , Andrew Morton , Josh Triplett , Thomas Gleixner , Peter Zijlstra , rostedt , David Howells , Eric Dumazet , fweisbec , Oleg Nesterov , "Joel Fernandes, Google" , Linus Torvalds Message-ID: <2135064974.9081.1627496585724.JavaMail.zimbra@efficios.com> In-Reply-To: <20210728173715.GA9416@paulmck-ThinkPad-P17-Gen-1> References: <20210721202042.GA1472052@paulmck-ThinkPad-P17-Gen-1> <20210721202127.2129660-4-paulmck@kernel.org> <20210728173715.GA9416@paulmck-ThinkPad-P17-Gen-1> Subject: Re: [PATCH v2 rcu 04/18] rcu: Weaken ->dynticks accesses and updates MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4059 (ZimbraWebClient - FF90 (Linux)/8.8.15_GA_4059) Thread-Topic: Weaken ->dynticks accesses and updates Thread-Index: BoHMuKvfQXCwt8W17GsIqyHeJ9P0jg== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jul 28, 2021, at 1:37 PM, paulmck paulmck@kernel.org wrote: [...] > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 42a0032dd99f7..c87b3a271d65b 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -251,6 +251,15 @@ void rcu_softirq_qs(void) > rcu_tasks_qs(current, false); > } > > +/* > + * Increment the current CPU's rcu_data structure's ->dynticks field > + * with ordering. Return the new value. > + */ > +static noinstr unsigned long rcu_dynticks_inc(int incby) > +{ > + return arch_atomic_add_return(incby, this_cpu_ptr(&rcu_data.dynticks)); > +} > + [...] > @@ -308,7 +317,7 @@ static void rcu_dynticks_eqs_online(void) > > if (atomic_read(&rdp->dynticks) & 0x1) > return; Can the thread be migrated at this point ? If yes, then the check and the increment may happen on different cpu's rdps. Is that OK ? > - atomic_inc(&rdp->dynticks); > + rcu_dynticks_inc(1); > } Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com