[gdal-dev] GDAL using Nvidia - won't use OpenCL

[Jonathan Williams]

Hello,
I've been trying to compile GDAL with OpenCL support for an Nvidia
gt555m (this is an Alienware m14x r1 laptop) on Ubuntu desktop (I wanted
to run it headless, but Ubuntu server failed to boot with the Nvidia
drivers and without X installed).

Per the instructions at various sites, including here:
https://wiki.tiker.net/OpenCLHowTo , I installed Ubuntu packages
nvidia-346, nvidia-346-uvm, nvidia-libopencl1-346 and
nvidia-opencl-icd-346. Other combinations seemed to fail, including
adding nvidia-opencl-dev, and more recent Ubuntu Nvidia driver versions
didn't include the uvm package (I think the current driver is the 361
series).

So, after installing these packages and making sure everything was in
order in /etc/OpenCL/vendors, I verified OpenCL was functional using
test packages like MandelGPU/MandelCPU. The OpenCL speedup was obvious
using these tests.

After a lot of trial-and-error compilations, this is my configuration
for GDAL with OpenCL:

./configure \
--prefix=/usr \
--disable-rpath \
--with-threads=yes \
--with-ogr \
--with-geos \
--without-libtool \
--with-libz=internal \
--with-libtiff=internal \
--with-geotiff=internal \
--with-pg=/usr/bin/pg_config \
--with-expat-lib=/usr/lib/x86_64-linux-gnu/libexpat.so \
--with-netcdf=/usr/lib \
--with-png=internal \
--with-jpeg=internal \
--with-gif=internal \
--without-kakadu \
--without-mrsid \
--without-jp2mrsid \
--with-liblzma=yes \
--with-curl=/usr/lib/x86_64-linux-gnu \
--with-ecw=/usr/local/hexagon \
--with-python=yes \
--with-hide-internal-symbols \
--with-jasper=/usr/local \
--with-openjpeg=/usr/local \
--with-opencl=yes \
--with-opencl-include=/usr/include \
--with-opencl-lib="-L/usr/lib/x86_64-linux-gnu -lOpenCL"

While I did get a couple of errors with this, they seem unrelated to
anything important (complaining of a zero-length gnu_printf format
string, ./config.rpath not existing, and GDALmake.opt.in ignoring the
--datarootdir setting), and a look at the output indicates OpenCL
support is selected.

Compilation itself completes with no obvious errors, and the resulting
functions run correctly. However, there is no speedup from using -wo
"USE_OPENCL=TRUE" over -wo "USE_OPENCL=FALSE", nor is there any effect
seen using nvidia-smi monitoring.

The GDALWARP command I'm running is this:
gdalwarp -srcnodata 9999 -dstnodata 9999 -t_srs EPSG:4326 -of GTiff -tr
0.03 0.03 -r cubicspline -multi -wo "USE_OPENCL=TRUE" tmp.grib2 tmp.tif

vs.

gdalwarp -srcnodata 9999 -dstnodata 9999 -t_srs EPSG:4326 -of GTiff -tr
0.03 0.03 -r cubicspline -multi -wo "USE_OPENCL=FALSE" tmp.grib2 tmp.tif


This system has four cores and is multithreading, so -wo
"NUM_THREADS=ALL_CPUS" does produce a speedup. But again, USE_OPENCL
does not. In fact, the program is entirely functional and does exactly
what I want, except for opencl functionality.

I'm at a bit of a loss as to what might be wrong. I've tried various
combinations of the with-opencl flags. I'm running all functions as
root, and have tried modprobe nvidia-uvm. No errors, no debug problems
noted, it just won't use the GPU. Part of my problem is I'm not sure
what problems would produce an error, and what just would fail silently.

Any insight would be appreciated!

Best regards,
Jonathan Williams