Slow memory access when using OpenCL without X11

[Alex Deucher]

I think you are probably using the CPU for OCL in the remote login
case.  When you log into the desktop, the permissions on the device
nodes get changed dynamically to support accelerated rendering.  You
probably need to change the permissions on the device nodes manually
if you are not logging into the desktop.

Alex

On Fri, Mar 8, 2019 at 2:43 PM Lauri Ehrenpreis <laurioma at gmail.com> wrote:
>
> Hi!
>
> I am using Ryzen 2400G with Gigabyte AMD B450 AORUS board. I have latest bios, ubuntu 18.04 and latest mainline kernel (5.0.0-050000-generic) installed. Also I have rocm-dev 2.1.96 but no rock-dkms installed.
>
> I found that when I log in over ssh and try to use OpenCL (doing clCreateContext is enough) then cpu memory accesses after that will slow down by 100x.
> If I connect HDMI cable and log in to desktop mode then this does not happen. Also if I don't call clCreateContext then everything works properly.
>
> Attached the test program and kernel log also. Test works like that :
> g++ cl_slow_test.cpp -o cl_slow_test -I /opt/rocm/opencl/include/ -L /opt/rocm/opencl/lib/x86_64/  -lOpenCL
> lauri at rv:~$ ./cl_slow_test 0 5
> speed 7003.145508 avg 7003.145508 mbytes/s
> speed 8427.357422 avg 7715.251465 mbytes/s
> speed 9203.049805 avg 8211.184570 mbytes/s
> speed 9845.956055 avg 8619.877930 mbytes/s
> speed 9882.748047 avg 8872.452148 mbytes/s
> lauri at rv:~$ ./cl_slow_test 1 5
> got 1 platforms 1 devices
> speed 1599.803589 avg 1599.803589 mbytes/s
> speed 1665.426392 avg 1632.614990 mbytes/s
> speed 146.137253 avg 1137.122437 mbytes/s
> speed 121.056877 avg 883.106018 mbytes/s
> speed 122.428970 avg 730.970581 mbytes/s
>
> I also tried latest amd-staging kernel https://github.com/M-Bab/linux-kernel-amdgpu-binaries and it had the same issue.
>
> Can anyone point me into right direction?
>
> Br,
> Lauri
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