Re: netperf & transmit path performance

From: Andi Kleen (ak@suse.de)
Date: Wed May 31 2000 - 13:08:34 EST


Kallol Biswas <kallol@bugula.fpk.hp.com> writes:
>
> Over a half duplex 10Mbps connection:
> TCP STREAM TEST to 198.168.10.67
> Recv Send Send Utilization Service Demand
> Socket Socket Message Elapsed Send Recv Send Recv
> Size Size Size Time Throughput local remote local remote
> bytes bytes bytes secs. 10^6bits/s % L % L us/KB us/KB
>
> 57344 57344 4096 300.07 6.96 3.52 2.16 41.461 101.728
>
> I am a bit concerned about the throughput over half duplex 10Mbps connection.
> Could some body tell how throughput can go low at 10Mbps?

Collisions of the data with the acks. The TCP ack clock gets out of sync.
 
>
> Simon Andrew Boggi got similar result over a half duplex connection
> with eepro100.
>
> With 21143 based card we get the throughput around
> 9.2 on 10Mbps. I do not know if there is any problem with 82559 in half duplex mode.

The 21143 uses a special patented Ethernet collision backoff algorithm that
works better than the normal backoff. The 82559 probably doesn't.

Morale: half duplex hurts.

-Andi

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