[Beignet] CL_MEM_USE_HOST_PTR involve extra copy?

[Guo, Yejun]

Just need to invoke clMapxx function before you access the host ptr from CPU side, and invoke clUnmapxx function after the CPU access. There is no extra copy inside clMap/Unmapxx if all the conditions are satisfied. You can refer to the code in runtime_use_host_ptr_buffer.cpp under beignet/utests.


From: spring_wind [mailto:spring_wind at yeah.net]
Sent: Wednesday, December 03, 2014 10:02 AM
To: Guo, Yejun
Cc: beignet at lists.freedesktop.org
Subject: Re:RE: [Beignet] CL_MEM_USE_HOST_PTR involve extra copy?

You mean if I use CL_MEM_USE_HOST_PTR and host ptr is page aligned, I change the data pointed by host ptr from CPU side, I don't have to do any flush opertaion or I should still call clMapxx function?




在 2014-12-03 08:37:15，"Guo, Yejun" <yejun.guo at intel.com<mailto:yejun.guo at intel.com>> 写道：

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<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<mailto: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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