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 722DFECDFBB for ; Thu, 19 Jul 2018 00:32:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1997720850 for ; Thu, 19 Jul 2018 00:32:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Nt/bdHgc" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1997720850 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 S1730096AbeGSBMf (ORCPT ); Wed, 18 Jul 2018 21:12:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:36242 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729309AbeGSBMe (ORCPT ); Wed, 18 Jul 2018 21:12:34 -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 CCF7E20661; Thu, 19 Jul 2018 00:32:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1531960329; bh=Ge6huWjWpmEFZuYAvn0G8qBZRWfPO/J3Qlt6nO0E0j0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Nt/bdHgc1/784+mJYWYc21Q5+JyTJZqhfBgurCM1Zyk/Fuq3U8Tk5n3611sLlDWlP +74XSzPdYcTgk38S+3G6DBxBAESkfujduq9JDpcIBL83oFJLIfnmQO/czhSqfW/pCR itx7+Egs2HRUhosMOy70b4X8yfhzNssDmm+bsxlI= Date: Thu, 19 Jul 2018 02:32:06 +0200 From: Frederic Weisbecker To: David Woodhouse Cc: paulmck@linux.vnet.ibm.com, Peter Zijlstra , mhillenb@amazon.de, linux-kernel , kvm Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested Message-ID: <20180719003205.GB5595@lerouge> References: <20180709203441.GE3593@linux.vnet.ibm.com> <1531168538.26547.5.camel@infradead.org> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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. Thanks.