Troubleshooting¶
Template Operators Cannot Be Found¶
The compiler omits the code of a template class method if that method
is not used in the code. This is a C++ issue and may cause
inconvenience when you want to invoke the omitted function. This
issue is seen in SYCL* because the basic classes (range, id,
nd_range, accessor, and others) are templates that have
several overloaded operators. Examples:
p index
Output:
$1 = cl::sycl::id<1> = {32}
p index + 5Output:
Could not find operator +.
As a solution, you can explicitly instantiate a template class in
your source. Then the methods of the template instance are available
in the binary. The instantiations can be surrounded with
#ifndef NDEBUG and #endif to avoid code bloat in release
builds. Example:
#ifndef NDEBUG
template class cl::sycl::id<1>;
template class cl::sycl::id<2>;
template class cl::sycl::id<3>;
template class cl::sycl::range<1>;
template class cl::sycl::nd_range<1>;
#endif // #ifndef NDEBUG
Accessor Operator [] Cannot Be Resolved¶
Elements of an accessor object cannot be accessed using the
multi-dimensional access syntax during expression evaluation. See
example below:
print anAccessor[5][3][4]
Example output:
Cannot resolve function operator[] to any overloaded instance
Instead, use an id object:
print workItemId
Example output:
$1 = cl::sycl::id<3> = {5, 3, 4}
print anAccessor[workItemId]
Example output:
$2 = 1234
Kernel Stops Responding¶
If the kernel that is offloaded to a GPU stops responding:
Check whether there are any stray `gdbserver-gt` processes running in the background:
ps -u $USER | grep gdbserver-gt
Stop background `gdbserver-gt` processes, if there are any:
killall -9 gdbserver-gt
Breakpoint Is Not Hit¶
If the breakpoints defined inside the kernel are not hit when running on a GPU, reset the GPU device (requires root access):
Unload the `igfxdcd` driver
modprobe -r igfxdcd
Reset the device
echo 0xffffffff | tee /sys/kernel/debug/dri/0/i915_wedged
Load the `igfxdcd` driver again
modprobe igfxdcd
If the breakpoints defined inside the kernel are not hit when running on a GPU, and Virtualization technology for directed I/O (VT-d) is enabled, disable VT-d through the BIOS menu.
Debug companion driver is not supported with VT-d enabled.