Try to run stlbm

[lanwatch]

stlbm is a very good example of high-performance scientific computation using C++ which can be offloaded sucessfully to accelerators with top-notch performance.

I have tried to compile it using oneDPL, by modifying the cavity.cpp source to add the

#include <oneapi/dpl/execution>
#include <oneapi/dpl/algorithm>
#include <sycl/sycl.hpp>

includes before the standard ones, and defining a policy like:

static sycl::queue q;
static const auto mypolicy = dpl::execution::make_device_policy(q);

which then gets passed to the std::for_each invocations, instead of std::execution::par_unseq.

When doing that I get a rather long C++ error that boils down to:

/work/stlbm/apps/cavity.cpp:300:9: note: in instantiation of function template specialization 'oneapi::dpl::for_each<const oneapi::dpl::execution::device_policy<> &, std::array<double, 19> *, twopop_aos_bgk_unrolled::LBM>' requested here
  300 |         for_each(mypolicy, lattice, lattice + dim.nelem, lbm);
      |         ^
/work/oneDPL/include/oneapi/dpl/pstl/hetero/dpcpp/unseq_backend_sycl.h:90:5: note: candidate template ignored: substitution failure [with _ItemId = size_t, _Ranges = <const oneapi::dpl::__ranges::guard_view<std::array<double, 19> *> &>]: no matching function for call to object of type 'const twopop_aos_bgk_unrolled::LBM'
   90 |     operator()(const _ItemId __idx, _Ranges&&... __rngs) const -> decltype(__f(__rngs[__idx]...))

Seems like the argument to LBM::operator() should be a CellData = std::array<double, 19> instead of a std::array<double, 19> * (I believe, from cursory examination of the guard_view class). Maybe some "type dressing" has gone wrong?

[MikeDvorskiy]

Hello @lanwatch ,
Firstly,
It seems you pass into for_each algorithm a data type (aka std::array<double, 19> * ), which is not supported by oneDPL.

OneAPI library documentation tells:

"You can use one of the following ways to pass data to an algorithm executed with a device policy:

• oneapi:dpl::begin and oneapi::dpl::end functions
• Unified shared memory (USM) pointers and std::vector with USM allocators
• Iterators of host-side std::vector
  "
  Secondly, what is a twopop_aos_bgk_unrolled::LBM type?
  Probably, you should add const modificator for LBM::operator(..) ?