Re: How to use IP/UDP/TCP checksum offload HW?

[Grant Edwards <grant.b.edwards@xxxxxxxxx>]

On 2011-06-07, Laurie Gellatly <laurie.gellatly@xxxxxxxxx> wrote:

> I tried to enable this before without success.

Ah yes, I saw your (unanswered) post from a few years back asking
about this.  I was hoping there had been some progress since then.

> I agree that its a waste of processor time when it can be performed
> in hardware.

The last time I did some profiling, IP checksum calculation was a
pretty significant bottleneck for TCP throughput.  Back in the NetBSD
stack days, I got about a 20% improvement in throughput by writing my
own assembly-language IP checksum routine for ARM7.  The FreeBSD C
implementation and more recent versions of gcc do almost as well as
hand-tuned assembly, but it's still a big percentage of CPU usage in
TCP communications -- and it will be even worse now that I have a chip
that does scatter-gather DMA.  A part for US $4 that has IP checksum
offloading and scatter-gather DMA.  Back when I was a new grad...

> Must we look at the latest BSD code to see how to implement this?

Maybe.  Or there might be a simpler way to do it.  I would guess that
the current FreeBSD has an API to configure this on a per-interface
basis at run-time.

If we can assume that there is only one external interface, then we
don't need any API or runtime checks, just a few strategic #if/#endif
pairs and some CDL to control them.

-- 
Grant


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