Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp]

[Artem Belevich]

On 7/8/08, Robert Watson <rwatson at freebsd.org> wrote:
>  There were some patches floating around for if_em to do a prefetch of the
> first bit of packet data on packets before handing them up the stack.  My

I found Andre Oppermann's optimization patch mentioned in july 2005
status report:
http://lists.freebsd.org/pipermail/freebsd-announce/2005-July/001012.html
http://www.nrg4u.com/freebsd/tcp_reass+prefetch-20041216.patch

Is that the patch you had in mind?

In the report Andre says: "Use [of prefetch] in both of these places
show a very significant performance gain but not yet fully
quantified."

"very significant" bit looks promising. Unfortunately, it does not
look like prefetch changes in the patch made it into official kernel.
I wonder why.

It should be easy enough to apply prefetch-related changes and see
if/how it affects forwarding performance.

--Artem