<div style="line-height:1.7;color:#000000;font-size:14px;font-family:Arial"><br><div>I noticed that in kernel's source(3.12.13) drm_clflush_page used clflush instruction.<br>I wonder whether the clfush instruction only push data to LLC or RAM? If it is RAM, is it needless since CPU and GPU share LLC.<br><br>We are planning to use beignet to accelerate video analysis and image processing. The data flow will involve input and output between GPU and CPU, we expect it will be not a bottleneck.<br></div><br><pre>At 2014-12-03 10:36:28, "Zhigang Gong" <zhigang.gong@linux.intel.com> wrote: >On Wed, Dec 03, 2014 at 10:44:26AM +0800, spring_wind wrote: >> 1. clCreateBuffer(CL_MEM_USE_HOST_PTR) >> 2. clMapxx-->change the data pointed by host ptr--->clUnmapxxx >> >> Is that right? >The usual use scenario is as below: > >1. clCreateBuffer(CL_MEM_USE_HOST_PTR) >2. clEnqueueNDRangeKernel() to enqueue some kernel to do some > computation on GPU side and write to the above buffer. >3. clEnqueueMapBuffer() the buffer, and do some computation > on CPU side and modify the buffer content pointed by host_ptr. >4. clEnqueueUnmapBuffer() to give the buffer back to GPU. > >The step 3 and 4 are synchronization points defined by OpenCL >spec which are mandatory on all platforms to access a buffer >pointed by host_ptr shared by GPU and CPU. At step3, not only >a GPU cache flush (flush from GPU's L3 cache to CPU's LLC cache), >but also need to wait for all the kernel enqueued in step 2 >to be finished. > > >> >> I think clUnmapxx must contain cache flush operation although it may not involve extra copy, correct me if am wrong. > >You are right. >The cache flush is always a must when we switch between GPU >domain and CPU domain. But you can see, the above flush is >not so heavy, as it's not a flush between cache and slow >memory. > >> I am very concerned about the beignet performance on our product. > >You are welcome to share your detail concerns with us if possible. >And there are also some performance hint in the 'docs/optimization-guide.mdwn'. >We will continue to update that document. > >Thanks, >Zhigang Gong. > >> >> >> >> >> >> >> >> 在 2014-12-03 10:14:10，"Guo, Yejun" <yejun.guo@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@yeah.net] >> Sent: Wednesday, December 03, 2014 10:02 AM >> To: Guo, Yejun >> Cc:beignet@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@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@lists.freedesktop.org] On Behalf Of spring_wind >> Sent: Tuesday, December 02, 2014 8:38 PM >> To:beignet@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? >> >> >> >> > >> _______________________________________________ >> Beignet mailing list >> Beignet@lists.freedesktop.org >> http://lists.freedesktop.org/mailman/listinfo/beignet > >_______________________________________________ >Beignet mailing list >Beignet@lists.freedesktop.org >http://lists.freedesktop.org/mailman/listinfo/beignet </pre></div><br><br><span title="neteasefooter"><span id="netease_mail_footer"><span title="neteasefooter"><span id="netease_mail_footer"><a href="#" target="_blank"></a></span></span> </span></span>