netdev - Re: TSO on veth device slows transmission to a crawl

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Message-ID: <5525634A.10207@hp.com>
Date:	Wed, 08 Apr 2015 10:20:10 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Jan Engelhardt <jengelh@...i.de>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	Linux Networking Developer Mailing List <netdev@...r.kernel.org>
Subject: Re: TSO on veth device slows transmission to a crawl

On 04/08/2015 10:09 AM, Jan Engelhardt wrote:
> The problem won't manifest with netperf even if run for extended
> period (60 seconds). netperf is probably too smart, exploiting some
> form of parallelism.

Heh - I rather doubt netperf is all that smart.  Unless you use the 
likes of the -T global option to bind netperf/netserver to specific 
CPUs, it will just blythly run wherever the stack/scheduler decides it 
should run.

It is though still interesting you don't see the issue with netperf.  I 
don't know specifically how xinetd-chargen behaves but if it is like the 
chargen of old, I assume that means it is sitting there writing one byte 
at a time to the socket, and perhaps has TCP_NODELAY set.  If you want 
to emulate that with netperf, then something like:

netperf -H <receiver> -t TCP_STREAM -- -m 1 -D

would be the command-line to use.

happy benchmarking,

rick jones
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