[Beignet] CL_MEM_USE_HOST_PTR involve extra copy?

[spring_wind]

1. clCreateBuffer(CL_MEM_USE_HOST_PTR)
2. clMapxx-->change the data pointed by host ptr--->clUnmapxxx

Is that right?

I think clUnmapxx must contain cache flush operation although it may not involve extra copy, correct me if am wrong.
I am very concerned about the beignet performance on our product.







在 2014-12-03 10:14:10，"Guo, Yejun" <yejun.guo at intel.com> 写道：


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> 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] 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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