Message-Id: <200307221319.h6MDJVgf007961@turing-police.cc.vt.edu>
To: Matthew Hunter <matthew@infodancer.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.4.21, NFS v3, and 3com 920 
In-Reply-To: Your message of "Tue, 22 Jul 2003 00:42:45 CDT."
             <20030722054245.GA768@infodancer.org> 
From: Valdis.Kletnieks@vt.edu
References: <20030722054245.GA768@infodancer.org>
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Date: Tue, 22 Jul 2003 09:19:31 -0400
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On Tue, 22 Jul 2003 00:42:45 CDT, Matthew Hunter <matthew@infodancer.org>  said:

> Running more tests, it turns out the speed problem is isolated to 
> the one machine, and only to *receiving* data.  Sending goes at 
> 8 M/s to other machines from the client machine.  Sending from 
> any machine to the client machine is slowed down, not just from 
> the server.

These symptoms sound suspiciously like a 100BaseT auto-negotiation
problem.  With some combinations of gear, if one end is set to auto-negotiate
and the other end is nailed to full/half duplex (sorry, can't remember which and
I've not my caffiene yet), things go horribly wrong and many packets
dissapear silently on transmission, forcing retransmit timeouts and bad
throughput.  Basically, you end up with one end thinking it's full duplex,
the other end at half - and if the full duplex side ever sends a packet while
the half side is sending, the packet's lost.

Try nailing the devices on both ends of the cat-5 to the same thing (full or
half).  This can of course be interesting if you have an unmanaged hub that
doesn't give you a choice...


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