Messages in this thread | | | Date | Thu, 10 Feb 2000 15:46:16 -0800 | From | Pete Wyckoff <> | Subject | Re: Gigabit Linux Server Bottlenecks |
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Jes.Sorensen@cern.ch said: > >>>>> "Alexey" == kuznet <kuznet@ms2.inr.ac.ru> writes: > > >> There is no point in using it for transmit since the Linux TCP > >> stack currently doesn't support this. > > Alexey> Hmm... Are you sure? Until now I thought exaclty the same with > Alexey> opposite sign. 8) Namely: there are no reasons to awake the > Alexey> feature in TCP, because no drivers support this. > > Well in order to use it and really gain on it for transmit, you want > scatter/gather skbuffs, something which I really want to look at > (provided I can find the time). If you are doing the data copy anyway, > there checksum is almost free.
Agreed. Back in the early 2.2 days I changed the kernel in a generic way not to checksum outgoing TCP/UDP packets if it knew the card could handle it, and experimented using a Packet Engines Hamachi gigE. The changes to the stack are fairly small, and the gains are near negligible (max 5% faster) since a checksum while copying is indeed free.
The curious might see http://dancer.ca.sandia.gov/~pw, but I'd much rather see the card DMA the unchecksummed payload directly from userspace.
-- Pete
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