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Date:      Wed, 23 Apr 1997 10:16:10 -0400 (EDT)
From:      Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
To:        Sujal Patel <smpatel@prognet.com>
Cc:        current@freebsd.org
Subject:   Possible networking bug in 2.2.1-Release
Message-ID:  <199704231416.KAA17910@khavrinen.lcs.mit.edu>
In-Reply-To: <Pine.BSF.3.95.970423000915.12595A-100000@sujal.prognet.com>
References:  <Pine.BSF.3.95.970423000915.12595A-100000@sujal.prognet.com>

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<<On Wed, 23 Apr 1997 00:24:26 -0700 (PDT), Sujal Patel <smpatel@prognet.com> said:

>         /*
>          * Verify that we have any chance at all of being able to queue
>          *      the packet or packet fragments
>          */
>         if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >= 
>		ifp->if_snd.ifq_maxlen) {
>                         error = ENOBUFS;
>                         goto bad;
>         }

This code is bogus, but it is unlikely to be the problem that you are
seeing.

There are three things wrong with this code:

1) It has a slow divide.
2) Fragments are a case to worry about on the slow path.
3) It knows far too much about the drop-tail queueing strategy.

(3) really bites, and when I implemented RED last year I tossed it
completely.  Unfortunately, my RED work has not made it into the main
line of FreeBSD yet.  I hope it will, some day, but it may take a
while before I have an environment where I can test it again.

-GAWollman

--
Garrett A. Wollman   | O Siem / We are all family / O Siem / We're all the same
wollman@lcs.mit.edu  | O Siem / The fires of freedom 
Opinions not those of| Dance in the burning flame
MIT, LCS, CRS, or NSA|                     - Susan Aglukark and Chad Irschick



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