From owner-svn-src-head@FreeBSD.ORG Sat Mar 28 18:18:39 2015 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 813211F6; Sat, 28 Mar 2015 18:18:39 +0000 (UTC) Received: from cell.glebius.int.ru (glebius.int.ru [81.19.69.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "cell.glebius.int.ru", Issuer "cell.glebius.int.ru" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id DB57E2D5; Sat, 28 Mar 2015 18:18:37 +0000 (UTC) Received: from cell.glebius.int.ru (localhost [127.0.0.1]) by cell.glebius.int.ru (8.14.9/8.14.9) with ESMTP id t2SIIXkI031766 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sat, 28 Mar 2015 21:18:33 +0300 (MSK) (envelope-from glebius@FreeBSD.org) Received: (from glebius@localhost) by cell.glebius.int.ru (8.14.9/8.14.9/Submit) id t2SIIXBB031765; Sat, 28 Mar 2015 21:18:33 +0300 (MSK) (envelope-from glebius@FreeBSD.org) X-Authentication-Warning: cell.glebius.int.ru: glebius set sender to glebius@FreeBSD.org using -f Date: Sat, 28 Mar 2015 21:18:33 +0300 From: Gleb Smirnoff To: John-Mark Gurney Subject: Re: svn commit: r280759 - head/sys/netinet Message-ID: <20150328181833.GX64665@FreeBSD.org> References: <201503271326.t2RDQxd3056112@svn.freebsd.org> <20150328083443.GV64665@FreeBSD.org> <20150328172313.GC51048@funkthat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150328172313.GC51048@funkthat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Fabien Thomas X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 28 Mar 2015 18:18:39 -0000 On Sat, Mar 28, 2015 at 10:23:13AM -0700, John-Mark Gurney wrote: J> > On Fri, Mar 27, 2015 at 01:26:59PM +0000, Fabien Thomas wrote: J> > F> Author: fabient J> > F> Date: Fri Mar 27 13:26:59 2015 J> > F> New Revision: 280759 J> > F> URL: https://svnweb.freebsd.org/changeset/base/280759 J> > F> J> > F> Log: J> > F> On multi CPU systems, we may emit successive packets with the same id. J> > F> Fix the race by using an atomic operation. J> > F> J> > F> Differential Revision: https://reviews.freebsd.org/D2141 J> > F> Obtained from: emeric.poupon@stormshield.eu J> > F> MFC after: 1 week J> > F> Sponsored by: Stormshield J> > J> > The D2141 says that benchmarking were done in presence of IPSEC, which J> > of course is the bottleneck and performance of this instruction can't J> > be benchmarked in its presence. Anyway, I believe that results of J> > right benchmark would still show little difference between atomic and J> > non-atomic increment of a shared value. J> > J> > I think we can use per-cpu ID counters, each CPU incrementing its J> > own. If we start with random values, then probability of two packets with J> > the same ID emitting at the allowed timeframe will be acceptably small. J> J> Please do not use per-cpu id counters.. That will just push the J> duplicate ids to being more rare, but just as much of a problem... J> J> Please read: J> https://tools.ietf.org/html/rfc6864 J> J> And then implement one hased upon source/dest/protocol... I know about this RFC, but using per-cpu ID counter if a low hanging fruit and is improvement. What is important not only improvement in terms of lowering probability of collision, but also easy improvement in performance, since now global ip_id increment is a cache line thrasher. So, I don't see how existense of the RFC blocks introducing an easy improvement. And if anyone works on implementing the RFC, he shouldn't care what is in head before his work, either global or per-cpu counter. -- Totus tuus, Glebius.