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=-2.1 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 BF6EFC0650F for ; Mon, 5 Aug 2019 08:07:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9810F20818 for ; Mon, 5 Aug 2019 08:07:58 +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="GPQWyTvO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727723AbfHEIH5 (ORCPT ); Mon, 5 Aug 2019 04:07:57 -0400 Received: from merlin.infradead.org ([205.233.59.134]:47256 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726423AbfHEIH5 (ORCPT ); Mon, 5 Aug 2019 04:07:57 -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=hQA/rHY648PLuDHdt0h8sdeUqJlY++q1WEQC024LSPw=; b=GPQWyTvOO6m8SdhjgY7gIUtSt 8td4m7e5ShiEOi/gFXT67z1QlfvbOoXqXC94vtc6tPLADjYpr/T03SlVHwhCdrgD6wqDo2qx0PsXl y4Vvp6xJkj13Qr2DwVoJt5jwnAOMe8w9tRojqYXOjZ3Cbg/2iisbX99BHQhNxz1fv457wOcGPw9Xp B9WjroZnZMHKQgZuQ4SsmJ90DIUyAOeyzcE1T6CGvFfUTRxKSD4KIzF+U4XOBUPA79baEvWVX8krj X844yml+HqGp/2tDNFgXFp+6k4DTWOjE11r0fyQxhdeOhPbeg2zgkgLda89/uSFox19DR8dNbrX1W U6zXwx/Yw==; 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 1huY1q-0006OZ-0J; Mon, 05 Aug 2019 08:07:38 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BA9AB20238109; Mon, 5 Aug 2019 10:07:36 +0200 (CEST) Date: Mon, 5 Aug 2019 10:07:36 +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: <20190805080736.GI2349@hirez.programming.kicks-ass.net> References: <20190802151435.GA1081@linux.ibm.com> <20190802151501.13069-14-paulmck@linux.ibm.com> <20190804144317.GF2349@hirez.programming.kicks-ass.net> <20190804144835.GB2386@hirez.programming.kicks-ass.net> <20190804184159.GC28441@linux.ibm.com> <20190804202446.GA25634@linux.ibm.com> <20190805041901.GA17621@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190805041901.GA17621@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 04, 2019 at 09:19:01PM -0700, Paul E. McKenney wrote: > On Sun, Aug 04, 2019 at 01:24:46PM -0700, Paul E. McKenney wrote: > > For whatever it is worth, the things on my list include using 25 rounds > > of resched_cpu() on each CPU with ten-jiffy wait between each (instead of > > merely 10 rounds), using waitqueues or some such to actually force a > > meaningful context switch on the other CPUs, etc. That really should not be needed. What are those other CPUs doing? > Which appears to have reduced the bug rate by about a factor of two. > (But statistics and all that.) Which is just weird.. > I am now trying the same test, but with CONFIG_PREEMPT=y and without > quite so much hammering on the scheduler. This is keying off Peter's > earlier mention of preemption. If this turns out to be solid, perhaps > we outlaw CONFIG_PREEMPT=n && CONFIG_NO_HZ_FULL=y? CONFIG_PREEMPT=n should work just fine, _something_ is off.