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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, 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 BD90AC43387 for ; Thu, 10 Jan 2019 20:25:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 894A4208E3 for ; Thu, 10 Jan 2019 20:25:42 +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="GaCjm/pW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729985AbfAJUZl (ORCPT ); Thu, 10 Jan 2019 15:25:41 -0500 Received: from merlin.infradead.org ([205.233.59.134]:51422 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727750AbfAJUZl (ORCPT ); Thu, 10 Jan 2019 15:25:41 -0500 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=Jog9ZwrILLUqYnYEM9yeKYKLdJpnoiz07dnT1UexYGE=; b=GaCjm/pWe5FgFqzGylW36JSuR w7j55huQNZGwupGWfX4BGLueRjgeK52utJbgYLT7kgUX5tp4N1JpdhF0GqHPpWmjWPk9fXyfms3ed y7YHRBCZmXsRv0Yo36PbZDpFr7iJ/brdxCOIp+Bl9fUKtqXhlWrknAO2HhpJKlW2na/liadrci1XX /0dR9U5gBh4dzywQ2pkKart0smy6VEFlyQcsMqMpU2rRVFQvx3OiDxD/buSI0WEGWqprnhdQ9TCZy oJAQEEIUGRJ45RyVTbac+XoBZ9mc7sJ2VVPos8cNFkoSH6KE1GPnLpMbaQ1FzkWklshY6NFgNypYa 0apYNOGvg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1ghgtU-00071q-1C; Thu, 10 Jan 2019 20:25:36 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 823F59844AF; Thu, 10 Jan 2019 21:25:33 +0100 (CET) Date: Thu, 10 Jan 2019 21:25:33 +0100 From: Peter Zijlstra To: Florian Westphal Cc: Anatol Pomozov , Dmitry Vyukov , paulmck@linux.ibm.com, LKML Subject: Re: seqcount usage in xt_replace_table() Message-ID: <20190110202533.GK2861@worktop.programming.kicks-ass.net> References: <20190108223746.shuwx3ro7cgwz7hh@breakpoint.cc> <20190110124123.GA21224@hirez.programming.kicks-ass.net> <20190110144812.mkbokbj2iyryj6lv@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190110144812.mkbokbj2iyryj6lv@breakpoint.cc> 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 Thu, Jan 10, 2019 at 03:48:12PM +0100, Florian Westphal wrote: > Peter Zijlstra wrote: > > Is performance a concern in this path? There is no comment justifying > > this 'creative' stuff. > > We have to wait until all cpus are done with current iptables ruleset. > > Before this 'creative' change, this relied on get_counters > synchronization. And that caused wait times of 30 seconds or more on > busy systems. > > I have no objections swapping this with a synchronize_rcu() if that > makes it easier. Would using synchronize_rcu() not also mean you can get rid of that xt_write_recseq*() stuff entirely? Anyway, synchronize_rcu() can also take a little while, but I don't think anywere near 30 seconds. > (synchronize_rcu might be confusing though, as we don't use rcu > for table->private), and one 'has to know' that all the netfilter > hooks, including the iptables eval loop, run with rcu_read_lock > held). A comment can help there, right?