Messages in this thread |  | | Date | Sat, 02 Sep 2000 16:20:58 -0600 | From | "Jeff V. Merkey" <> | Subject | Re: zero-copy TCP |
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Alan Cox wrote: > > > > Sounds like Linux - one DMA and one copy to user space. > > > > Alan, Please. I'm in your code and there are copies all over the > > place. I agree you have a "fast path" for most stuff, but there's all > > There arent copies all over the case for the paths that occur. Like 99.999% > of the time. Fragmented packets dont happen except for NFS (which is a rather > broken protocol anyway).
There are.
> > One DMA, one copy to user space > > > kinds of handles lookups, linear list searching like > > > > while (x) > > { > > x = x->next > > } > > timers are constructed to be close to O(1), the tcp hash isnt a linear lookup, > the socket operations from user space use file-> dereferences not a lookup
It is is there's a hash collision.
> > > nothing in TCPIP except at the stream head. Why do you need to copy > > data anyway to checksum an IP packet anyway? I noticed you do the right > > thing and keep the headers and data as separate fragments during header > > construction, so why do you need to copy data for checksumming? > > We dont copy for checksumming. We fold the single user space copy and the > checksum operation into one path, because on any modern CPU it costs precisely > the same to copy as to copy/checksum. > > I don't think you've actually sat and instrumented the TCP code
In Linux, no, in Netware, yes. I'm in your TCP code now and it's fairly large.
Jeff
> > Alan > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > Please read the FAQ at http://www.tux.org/lkml/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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