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SubjectRe: Early SPECWeb99 results on 2.5.33 with TSO on e1000

sorry for the late reply. catching up on kernel mail.

so all this TSO stuff looks v. v. similar to the IP-only fragmentation
that patricia gilfeather and i implemented on alteon acenics a couple of
years ago (see for a
general overview). it's exciting to see someone else take a stab on
different hardware and approaching some of the tcp-specific issues.

the main different, though, is that general purpose kernel development
still focussed on the improvements in *sending* speed. for real high
performance networking, the improvements are necessary in *receiving* cpu
utilization, in our estimation. (see our analysis of interrupt overhead
and the effect on receivers at gigabit speeds--i hope that this has become
common understanding by now)

i guess i can't disagree with david miller that the improvments in TSO are
due entirely to header retransmission for sending, but that's only because
sending wasn't CPU-intensive in the first place. we were able to get a
significant reduction in receiver cpu-utilization by reassembling IP
fragments on the receiver side (sort of a standards-based interrupt
mitigation strategy that has the benefit of not increasing latency the way
interrupt coalescing does).

anyway, nice work,


On Thu, 5 Sep 2002, David S. Miller wrote:

> It's the DMA bandwidth saved, most of the specweb runs on x86 hardware
> is limited by the DMA throughput of the PCI host controller. In
> particular some controllers are limited to smaller DMA bursts to
> work around hardware bugs.
> Ie. the headers that don't need to go across the bus are the critical
> resource saved by TSO.
> I think I've said this a million times, perhaps the next person who
> tries to figure out where the gains come from can just reply with
> a pointer to a URL of this email I'm typing right now :-)

todd underwood, vp & cto
oso grande technologies, inc.

"Those who give up essential liberties for temporary safety deserve
neither liberty nor safety." - Benjamin Franklin

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