GPU Track Fitting

[beomki-yeo]

The PR is still in WIP (and depends on #264). I didn't even generalize it for both CUDA and SYCL yet.
But I want to get some advises in advance because I am stuck right now.
The main problem was that I was forced to implement the template classes in the source file:
For example, traccc::cuda::fitting_algorithm is declared in traccc/device/cuda/include/traccc/cuda/fitting/fitting_algorithm.hpp and implemented in traccc/device/cuda/src/fitting/fitting_algorithm.cu
Because traccc::cuda::fitting_algorithm is a template class, it was necessary to explicitly instantiate explicitly the class with specific template parameters :/ (See the code below)

// Explicit template instantiation
using host_detector_type =
    detray::detector<detray::detector_registry::telescope_detector,
                     covfie::field>;
using device_detector_type =
    detray::detector<detray::detector_registry::telescope_detector,
                     covfie::field_view, detray::device_container_types>;
using b_field_t = typename host_detector_type::bfield_type;
using rk_stepper_type = detray::rk_stepper<b_field_t::view_t, transform3,
                                           detray::constrained_step<>>;
using device_navigator_type = detray::navigator<const device_detector_type>;
using device_fitter_type =
    kalman_fitter<rk_stepper_type, device_navigator_type>;
template class fitting_algorithm<device_fitter_type, host_detector_type>;

Instantiating the classes for every detector class is definitely not I want to do. I wonder if there is a workaround for this ?

[beomki-yeo]

I am also not sure if I can get rid of .cu implementation and put everything including kernels into the header file

[beomki-yeo]

I will be back after I make detray work with SYCL

[krasznaa]

In general I like it. But we'll unfortunately need to find some replacement for the recursive function call(s). At least for SYCL. (But I think CUDA would also benefit from not relying on recursive calls.)

[beomki-yeo]

But we'll unfortunately need to find some replacement for the recursive function call(s). At least for SYCL.

It will be resolved by acts-project/detray#369. There was only one recursive function from std::sort, and I implemented a custom sort function to work around it.

[krasznaa]

With some tremendous delay, let's finally push this in...

[krasznaa]

👍