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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 7CDD8C433FF for ; Sun, 4 Aug 2019 14:44:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4611B20844 for ; Sun, 4 Aug 2019 14:44:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="IVjn9fgQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726197AbfHDOoK (ORCPT ); Sun, 4 Aug 2019 10:44:10 -0400 Received: from merlin.infradead.org ([205.233.59.134]:43142 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726181AbfHDOoK (ORCPT ); Sun, 4 Aug 2019 10:44:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=5rdh5G3lzzyq4EoUCDQ5vzYWt2z2/ddaXxkgEfQ0PHo=; b=IVjn9fgQ9/E+g8+WjfQVMK8Q5 j3vCPYCzAnTsHuLB3r5Um+aCRhNQoONqJDIW+mm7keg+rMTJOYyuQx3tLtFpeCUwFnt4qPMdU/eJV Y7y4b2LNzuhyq3dJ2QdG42K6fm+WX1m2hC1UzI0/vL2zzszTBpt+WEc43P+4zqMHji7qRWpHAp/Jz 214HVmu6/gHGEDUGbm9p9pHYDE/TE3qnvT3YPoLCkfwD9GWuSMZmO9f/XnK5RwL7LlyrcgeXGx8q2 TvtPgbj3uCporq3u8KsFfM7TXQainyMrQ5LwTpdcZrHMtS+fb54fKAVLSRsGVIDaK2o6x47Sda/0g Es6Wam6GA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1huHjE-0007Le-Lx; Sun, 04 Aug 2019 14:43:21 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CAEA2202989CD; Sun, 4 Aug 2019 16:43:17 +0200 (CEST) Date: Sun, 4 Aug 2019 16:43:17 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH RFC tip/core/rcu 14/14] rcu/nohz: Make multi_cpu_stop() enable tick on all online CPUs Message-ID: <20190804144317.GF2349@hirez.programming.kicks-ass.net> References: <20190802151435.GA1081@linux.ibm.com> <20190802151501.13069-14-paulmck@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190802151501.13069-14-paulmck@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Aug 02, 2019 at 08:15:01AM -0700, Paul E. McKenney wrote: > The multi_cpu_stop() function relies on the scheduler to gain control from > whatever is running on the various online CPUs, including any nohz_full > CPUs running long loops in kernel-mode code. Lack of the scheduler-clock > interrupt on such CPUs can delay multi_cpu_stop() for several minutes > and can also result in RCU CPU stall warnings. This commit therefore > causes multi_cpu_stop() to enable the scheduler-clock interrupt on all > online CPUs. This sounds wrong; should we be fixing sched_can_stop_tick() instead to return false when the stop task is runnable?