Network Throughput Problem...

From: Matthew Faulkner
Date: Thu Oct 18 2007 - 11:42:39 EST


Hey all

I'm using netperf to perform TCP throughput tests via the localhost
interface. This is being done on a SMP machine. I'm forcing the
netperf server and client to run on the same core. However, for any
packet sizes below 523 the throughput is much lower compared to the
throughput when the packet sizes are greater than 524.

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. MBytes /s % S % S us/KB us/KB
65536 65536 523 30.01 81.49 50.00 50.00 11.984 11.984
65536 65536 524 30.01 460.61 49.99 49.99 2.120 2.120

The chances are i'm being stupid and there is an obvious reason for
this, but when i put the server and client on different cores i don't
see this effect.

Any help explaining this will be greatly appreciated.
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