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Date:      Fri, 28 Jul 2000 23:43:09 +0200
From:      sthaug@nethelp.no
To:        archie@whistle.com
Cc:        silby@silby.com, freebsd-net@FreeBSD.ORG, jlemon@FreeBSD.ORG
Subject:   Re: sub-optimal tcp_ouput() performance in the face of ENOBUFS
Message-ID:  <20394.964820589@verdi.nethelp.no>
In-Reply-To: Your message of "Fri, 28 Jul 2000 14:34:48 -0700 (PDT)"
References:  <200007282134.OAA27448@bubba.whistle.com>

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> I understand the scenario described by the commit message. What
> I don't understand about this commit is this: suppose the exact
> same scenario happens, except that instead of ip_output() returning
> ENOBUFS, it returns zero, BUT the packet is dropped anyway because
> of (say) an Ethernet collision.

A normal Ethernet collision does *not* result in a dropped packet -
simply a packet which is transmitted a few microseconds later by the
Ethernet hardware.

If the packet has not been successfully transmitted in 16 attempts,
it is indeed dropped - but this is (or should be!) an extremely rare
event.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no


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