[openib-general] sdp sockets and zcopy?

Wed Apr 28 14:09:43 PDT 2004

    Abhijit> Hello, when do SDP socket writes translate to Zcopy?

    Abhijit> looking at the code (ulp/sdp/*) it seems that write(2) on
    Abhijit> (sdp) socket fd's always happen via Bcopy mechanism
    Abhijit> unless AIO support is compiled in (and socket aio is used
    Abhijit> by the user app). is my understanding correct?

    Abhijit> because from the code, write(2) happens via
    Abhijit> tsSdpInetSend() which looks to be doing a copy into
    Abhijit> kernel space always. (i.e. using Bcopy method).

Hi, Libor (the main author of the SDP code) is out for a few days, so
I will try to answer for him.

You are correct that the current SDP code does zero-copy only for
asynch IO.  It should be possible to do blocking reads and writes into
zero-copy, but the current code treats both nonblocking and blocking
IO the same way.

Adding zero-copy for blocking IO has been on our to-do list for a
while but the work has not been done yet.  If you're interested in
working on this, you should try and coordinate with Libor when he gets
back next week.

 - Roland

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