Messages in this thread |  | | Date | Thu, 12 Sep 2002 01:28:34 -0600 (MDT) | From | Todd Underwood <> | Subject | Re: Early SPECWeb99 results on 2.5.33 with TSO on e1000 |
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folx,
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 http://www.cs.unm.edu/~maccabe/SSL/frag/FragPaper1/ 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,
t.
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. todd@osogrande.com
"Those who give up essential liberties for temporary safety deserve neither liberty nor safety." - Benjamin Franklin
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