15 Replies Latest reply on Jan 14, 2009 3:22 PM by rick.weber

    Double memory copy in CAL ? What about calCtxResCreate ?

    jean-claude
      Optimizing memory exchanges between CPU & GPU

      Hi ,

      I have some basic question related to explicit/implicit memory exchanges between CPU and the GPU

      Here is some case:

      CALresource  Mrem;
      calResAllocRemote1D(&Mrem, &device, 1, 1024, CAL_FORMAT_INT_1, CAL_RESALLOC_CACHEABLE);


      This should allocate a 1024 int buffer in the PCI memory zone, correct?
      Moreover we ask this resource to be cacheable to get better CPU R/W access perf.

      Now consider:

      CALuint ptchx = 0;
      CALuint *pMem;

      calResMap((CALvoid**)&pMem, &ptchx, Mrem, 0);
           for (int i=0; i<1024; i++) *pMem++ = i; // or whatever CPU treatment
      calResUnmap(Mrem);


      (0) Should Mrem have been allocated as a local GPU resource, my understanding is that an intermediate PCI memory zone would be implicitly allocated at calResMap and that this PCI zone would be implicitly copied to local GPU mem at calResUnmap. Right?

      (1) Now since here Mrem is a remote resource:
      Is the writing directly done in Mrem, or does it occur first on an
      intermediate PCI memory zone and then is implicitly copied  to Mrem at the time of CalResUnMap(Mrem)?? Should it be the case then we face a hidden double copy...

      (2) The documentation suggests that double copy can be avoided through careful use of "calCtxResCreate" which doesn't appear to be accessible in the SDK.
      Is "calCtxResCreate" a ghost API?? How to use it?

      Thanks

      Jean-Claude