Date: Thu, 15 Aug 2013 05:23:38 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Peter Wemm <peter@wemm.org> Cc: Lawrence Stewart <lstewart@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Lev Serebryakov <lev@freebsd.org>, FreeBSD Net <net@freebsd.org> Subject: Re: it's the output, not ack coalescing (Re: TSO and FreeBSD vs Linux) Message-ID: <20130815032338.GA74257@onelab2.iet.unipi.it> In-Reply-To: <CAGE5yCrdptEAK7y_qBM3Og9U45o1_0ZtN0ANXg6WwXNTqX-1GQ@mail.gmail.com> References: <520A6D07.5080106@freebsd.org> <520AFBE8.1090109@freebsd.org> <520B24A0.4000706@freebsd.org> <520B3056.1000804@freebsd.org> <20130814102109.GA63246@onelab2.iet.unipi.it> <587579055.20130814154713@serebryakov.spb.ru> <CAJ-VmokxgWKeuPFGEE-wzLcYpyt3Ua90JZH2BBTj39LoTSUsMg@mail.gmail.com> <CAGE5yCrdptEAK7y_qBM3Og9U45o1_0ZtN0ANXg6WwXNTqX-1GQ@mail.gmail.com>
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On Wed, Aug 14, 2013 at 12:40:19PM -0700, Peter Wemm wrote: > On Wed, Aug 14, 2013 at 11:11 AM, Adrian Chadd <adrian@freebsd.org> wrote: > > On 14 August 2013 04:47, Lev Serebryakov <lev@freebsd.org> wrote: > > > > > >> And we should invalidate this info on ARP/route changes, or connection > >> will be lost in such cases, am I right?.. So, on each such event code > >> should look into all sockets and check, if routing/ARP information is > >> still > >> valid for them. Or we should store lists of sockets in routing and ARP > >> tables... I don't know, what is worse. > >> > > > > .. or per-CPU copies of the ARP table.. ? > > Local cache at each consumer and check a generation number to see if > it needs to be re-validated before using. The obvious problem with > this though is that big networks tend to kill your caches. if you expect this to be problematic you can partition the entries and use a different generation number per cluster. Anyways if you really want to be guaranteed you need atomic reads on the generation numbers (or ticks), which I have heard are expensive on !i386/amd64 machines. This is why I would probably try to live with races (which for arp are a non problem). cheers luigi
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