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=-1.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_HIGH,URG_BIZ, USER_AGENT_MUTT autolearn=ham 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 9634DC468C6 for ; Thu, 19 Jul 2018 13:15:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 474F42084E for ; Thu, 19 Jul 2018 13:15:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ie9qnVVy" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 474F42084E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731800AbeGSN6U (ORCPT ); Thu, 19 Jul 2018 09:58:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:43862 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727487AbeGSN6U (ORCPT ); Thu, 19 Jul 2018 09:58:20 -0400 Received: from localhost (LFbn-NCY-1-241-207.w83-194.abo.wanadoo.fr [83.194.85.207]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BF26A20673; Thu, 19 Jul 2018 13:15:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1532006113; bh=Eld0MB2d5l2hQnQhLMaf53EFD0TiAyriU6rKi9aBvNU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Ie9qnVVy0i0Y1/tv/22rlneY1ZLJfs1VPuu4YC+VvB4MKcXOdegVKxECGsA6CzSQs WgkoFZMYdnC1MQf23UZP9cBIs5EgtFA0G1y8jJKdZQS9nTkc4smlNBfwn5bJY0uvao aWDlw0pJsEK6R6LeGxwebB8Sh4svJP7OSxkzO1/o= Date: Thu, 19 Jul 2018 15:15:10 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: David Woodhouse , Peter Zijlstra , mhillenb@amazon.de, linux-kernel , kvm Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested Message-ID: <20180719131509.GD5595@lerouge> References: <20180709204248.GF3593@linux.vnet.ibm.com> <1531169145.26547.8.camel@infradead.org> <20180709210532.GH3593@linux.vnet.ibm.com> <20180709220823.GA18045@linux.vnet.ibm.com> <1531319025.8759.57.camel@infradead.org> <20180711144303.GQ3593@linux.vnet.ibm.com> <20180711164952.GA29994@linux.vnet.ibm.com> <20180719003205.GB5595@lerouge> <20180719031152.GR12945@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180719031152.GR12945@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 18, 2018 at 08:11:52PM -0700, Paul E. McKenney wrote: > On Thu, Jul 19, 2018 at 02:32:06AM +0200, Frederic Weisbecker wrote: > > On Wed, Jul 11, 2018 at 06:03:42PM +0100, David Woodhouse wrote: > > > On Wed, 2018-07-11 at 09:49 -0700, Paul E. McKenney wrote: > > > > And here is an updated v4.15 patch with Marius's Reported-by and David's > > > > fix to my lost exclamation point. > > > > > > Thanks. Are you sending the original version of that to Linus? It'd be > > > useful to have the commit ID so that we can watch for it landing, and > > > chase this one up to Greg. > > > > > > As discussed on IRC, this patch reduces synchronize_sched() latency for > > > us from ~4600s to ~160ms, which is nice. > > > > > > However, it isn't going to be sufficient in the NO_HZ_FULL case. For > > > that you want a patch like the one below, which happily reduces the > > > latency in our (!NO_HZ_FULL) case still further to ~40ms. > > > > That is interesting. As I replied to Paul, we are already calling > > rcu_user_enter/exit() on guest_enter/exit_irqsoff(). So I'm wondering why > > you're seeing such an optimization by repeating those calls. > > > > Perhaps the rcu_user_* somehow aren't actually called from > > __context_tracking_enter()...? Some bug in context tracking? > > Otherwise it's a curious side effect. > > David is working with v4.15. Is this maybe something that has changed > since then? Hmm, nope I think the context tracking code hasn't changed for a while.