Subject: Re: Skipping TCP / UDP / IP checksums on loopback traffic
To: Jonathan Stone <>
From: Nathan J. Williams <>
List: tech-net
Date: 10/25/2004 12:39:06
Jonathan Stone <> writes:

> My take is, the benchmarks you allude to are deficient benchmarks.
> The answer to *that* is better benchmarks (e.g., netperf, or lmbench's
> network benchmark run over a point-to-point link between two hosts).

I tend to agree that changing this for the purpose of looking better
on benchmarks is somewhat bogus

But what is the virtue of doing the checksumming in this case at all?
I see a slight complexity advantage in checksumming everywhere, but
that's it.

> And (in case its not obvious): yes, I *do* have some interest in
> network-throughput benchmarks over local-loopback. Personally, I'm
> much less interested in those benchmarks if they elide checksumming.

I'm curious. Having said that the benchmarks this change targets are
deficient, what is it about your benchmarks for this case that is

Finally, I note that Jason's change included the ever-popular
sysctl knob for turning the checksumming back on. Would this address
your concern about your benchmarks? If not, I would like to advocate
its removal, because from where I stand there's no reason for this
behavior to be optional.

        - Nathan