[Beignet] CL_MEM_USE_HOST_PTR involve extra copy?

[Guo, Yejun]

Hi,

please check the latest code of beignet, there is no copy needed between CPU and GPU if the host_ptr provided by application is page aligned, and the page align limitation is expected to be removed some days later. You can also try CL_MEM_ALLOC_HOST_PTR to avoid the extra copy without align limitation.

Btw, this zero-copy is supported starting from linux kernel 3.16 and libdrm 2.4.58.


From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of spring_wind
Sent: Tuesday, December 02, 2014 8:38 PM
To: beignet at lists.freedesktop.org
Subject: [Beignet] CL_MEM_USE_HOST_PTR involve extra copy?

Hi:
Intel opencl optimization guide said using CL_MEM_USE_HOST_PTR can avoid extra copy between CPU and GPU, but I noticed that in beignet's implementation source it was not like that:
/* Copy the data if required */
  if (flags & CL_MEM_COPY_HOST_PTR || flags & CL_MEM_USE_HOST_PTR)
    cl_buffer_subdata(mem->bo, 0, sz, data);

Could someone give me an answer?

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