Date: Sat, 28 Mar 2015 17:45:20 +0000 From: "Bjoern A. Zeeb" <bz@FreeBSD.org> To: John-Mark Gurney <jmg@funkthat.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Gleb Smirnoff <glebius@freebsd.org>, src-committers <src-committers@freebsd.org> Subject: Re: svn commit: r280759 - head/sys/netinet Message-ID: <CCF2D383-E17B-4A3A-BFB8-F39FA9DAFDBC@FreeBSD.org> In-Reply-To: <20150328172313.GC51048@funkthat.com> References: <201503271326.t2RDQxd3056112@svn.freebsd.org> <20150328083443.GV64665@FreeBSD.org> <20150328172313.GC51048@funkthat.com>
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> On 28 Mar 2015, at 17:23 , John-Mark Gurney <jmg@funkthat.com> wrote: >=20 > 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>=20 >> 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> =20 >> F> Differential Revision: https://reviews.freebsd.org/D2141 >> F> Obtained from: emeric.poupon@stormshield.eu >> F> MFC after: 1 week >> F> Sponsored by: Stormshield >>=20 >> 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. >>=20 >> 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. >=20 > 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... >=20 > Please read: > https://tools.ietf.org/html/rfc6864 >=20 > And then implement one hased upon source/dest/protocol=E2=80=A6 and if someone is interested in reviving this as well (read the old = thread from then on net@) https://people.freebsd.org/~bz/20110313-01-rfc6056.diff =E2=80=94=20 Bjoern A. Zeeb Charles Haddon Spurgeon: "Friendship is one of the sweetest joys of life. Many might have failed beneath the bitterness of their trial had they not found a friend."
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