Date: Sat, 28 Mar 2015 10:23:13 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: Gleb Smirnoff <glebius@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Fabien Thomas <fabient@freebsd.org> Subject: Re: svn commit: r280759 - head/sys/netinet Message-ID: <20150328172313.GC51048@funkthat.com> In-Reply-To: <20150328083443.GV64665@FreeBSD.org> References: <201503271326.t2RDQxd3056112@svn.freebsd.org> <20150328083443.GV64665@FreeBSD.org>
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Gleb Smirnoff wrote this message on Sat, Mar 28, 2015 at 11:34 +0300: > On Fri, Mar 27, 2015 at 01:26:59PM +0000, Fabien Thomas wrote: > F> Author: fabient > F> Date: Fri Mar 27 13:26:59 2015 > F> New Revision: 280759 > F> URL: https://svnweb.freebsd.org/changeset/base/280759 > F> > F> Log: > F> On multi CPU systems, we may emit successive packets with the same id. > F> Fix the race by using an atomic operation. > F> > F> Differential Revision: https://reviews.freebsd.org/D2141 > F> Obtained from: emeric.poupon@stormshield.eu > F> MFC after: 1 week > F> Sponsored by: Stormshield > > The D2141 says that benchmarking were done in presence of IPSEC, which > of course is the bottleneck and performance of this instruction can't > be benchmarked in its presence. Anyway, I believe that results of > right benchmark would still show little difference between atomic and > non-atomic increment of a shared value. > > I think we can use per-cpu ID counters, each CPU incrementing its > own. If we start with random values, then probability of two packets with > the same ID emitting at the allowed timeframe will be acceptably small. Please do not use per-cpu id counters.. That will just push the duplicate ids to being more rare, but just as much of a problem... Please read: https://tools.ietf.org/html/rfc6864 And then implement one hased upon source/dest/protocol... Thanks. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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