topic Re:sycl::stream causing segfault? in Intel® oneAPI DPC++/C++ Compiler

sycl::stream causing segfault?

CFR — Thu, 09 Jul 2020 23:56:10 GMT

Given the following (example) source...

#include <CL/sycl.hpp> namespace sycl = cl::sycl; const int Nproc = 6; int main(int argc, char *argv[]) { sycl::device dev = sycl::cpu_selector().select_device(); sycl::queue q(dev); q.submit([&](sycl::handler& cgh) { sycl::stream sout {1024, 1024, cgh}; sout << "Kernel" << sycl::endl; cgh.parallel_for<class kernelCPU>( sycl::range<1> {Nproc}, [=] (sycl::item<1> item) { int idx = item.get_linear_id(); sout << idx << sycl::endl; } ); } ); }

... built/run as follows...

user@t570:~/OneAPI/SYCL$ dpcpp --version Intel(R) oneAPI DPC++ Compiler 2021.1-beta07 (2020.5.0.0604) Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /local/opt/inteloneapi/compiler/latest/linux/bin user@t570:~/OneAPI/SYCL$ make bug4 dpcpp -O3 -g -mavx2 -o bug4 bug4.cpp -lOpenCL -lsycl user@t570:~/OneAPI/SYCL$ ./bug4 PLEASE submit a bug report to https://software.intel.com/en-us/support/priority-support and include the crash backtrace. Segmentation fault (core dumped)

The offending line is the "sout << "Kernel" << sycl::endl;". Comment that out and the fault disappears.

I'm not sure if this is a dpc++ bug, or a "me" bug, but it said to report it so... (fyi I don't have priority support so I'm doing it here).

Re:sycl::stream causing segfault?

GouthamK_Intel — Fri, 10 Jul 2020 10:35:31 GMT

Hi,

As we discussed in your previous thread (https://community.intel.com/t5/Intel-oneAPI-Data-Parallel-C/std-ostream-lt-lt-vec-lt-T-length-gt-not-supoorted-in-OneAPI/m-p/1190955#M557).

The stream class is designed to use only within kernels in order to stream from the kernel back to the host CPU for printing via stdout.

The stream instance is constructed in host within the command group scope and takes maximum buffer size, maximum stream size, and command group handler instance as parameters.

cl::sycl::stream sout(<max_buffer_size>, <max_stream_size>, <cgh>);

maximum buffer size = the overall character stream that can be output in characters (a character is of size sizeof(char) bytes) during kernel invocation (the aggregate of outputs from all work items).

maximum stream size = this specifies the maximum size of the character stream (number of characters) that can be output within a work item before a flush must be performed (maximum number of characters that can be used in a single statement on the stream).

When strings are stream to the object within a kernel, the contents are stored on an internal cl_mem object until the kernel finishes execution. The output is then output to stdout when the stream object is destroyed by the runtime.

In the sample code provided by you, as sout<< () is getting invoked outside the kernel (parallel_for), it is causing the segmentation fault error. Whereas for the sout<<() which was invoked inside the kernel you don't see any issues.

Please let us know if the above information helped you.

Regards

Goutham

Re:sycl::stream causing segfault?

GouthamK_Intel — Wed, 15 Jul 2020 12:30:15 GMT

Hi,

Could you please confirm if your issue is resolved?

Regards

Goutham

Re: Re:sycl::stream causing segfault?

CFR — Fri, 17 Jul 2020 23:49:08 GMT

I understand my error. Thanks.

Re:sycl::stream causing segfault?

GouthamK_Intel — Mon, 20 Jul 2020 06:18:35 GMT

Hi,

Thanks for the confirmation.!

This issue has been resolved and we will no longer respond to this thread. If you require additional assistance from Intel, please start a new thread. Any further interaction in this thread will be considered community only.

Have a Good day.!

Thanks & Regards

Goutham