Subject: Re: ipv6 TSO
To: Matthias Scheler <>
From: Steven M. Bellovin <>
List: tech-net
Date: 11/21/2006 07:50:28
On Tue, 21 Nov 2006 09:41:25 +0000, Matthias Scheler <>

> On Tue, Nov 21, 2006 at 12:52:56AM +0100, Hubert Feyrer wrote:
> > On Mon, 20 Nov 2006, Matthias Scheler wrote:
> > >I've uploaded a 900MB file FTP over TCPv6 (using a kernel producing some
> > >extra debugging output when TSOv6 is used) and compared the SHA512 hashes
> > >of the source and destination file.
> > 
> > What was the time and cpu utilization difference (assuming that's the 
> > point of TSO)?
> I'm not sure how to measure that properly. As a quick test I used "rcp"
> to transfer a 768MB file over IPv6 over Gigabit ethernet to "/dev/null"
> on the remote machine:
Hmm -- try running some other CPU-bound process in the background.  When
the file transfer is finished, kill it and see how much CPU time it got
(or, perhaps, how many times through some loop it got).

Rationale: checksum time is kernel time that's probably taken ultimately
from the idle time.  Your application used 20% of the CPU, so maybe it
would show as 20% of the checksum time being billed to you, but that's not
clear -- in the steady state, the application's write() calls are going to
be correlated with when checksum calculations are done.

		--Steven M. Bellovin,