Messages in this thread |  | | Date | Sat, 02 Sep 2000 16:47:33 -0600 | From | "Jeff V. Merkey" <> | Subject | Re: zero-copy TCP |
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Andi Kleen wrote: > > On Sat, Sep 02, 2000 at 04:28:18PM -0600, Jeff V. Merkey wrote: > > > > > > Alan Cox wrote: > > > > > > 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. > > > > You stated in an earlier message you copied the data when you caclulated > > the TCPIP checksum? No you say you don't. Perhaps I misunderstood. > > Linux always does a single copy for TCP, and the checksum is folded into > that. Doing just the checksum alone wouldn't be much less costly. > > [Note this is only true for 2.4 in the fast path, 2.2 RX usually does > checksum and copy-to-user separated, unless you have hardware RX checksumming > > For TX we always do a single copy checksum out of user space or out of the > page cache when you use sendfile or mmap]
This makes sense.
Jeff
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