Messages in this thread |  | | Date | Sun, 3 Sep 2000 00:39:38 +0200 | From | "Andi Kleen" <> | Subject | Re: zero-copy TCP |
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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]
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