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Alpaka n-body changes #822

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merged 4 commits into from
Jan 4, 2024
Merged

Alpaka n-body changes #822

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ed2ec19
Use SoA MB for global memory
bernhardmgruber Jan 3, 2024
6e53f52
Optimize alpaka n-body for slides/thesis
bernhardmgruber Jan 4, 2024
a25149e
Print global memory for alpaka devices
bernhardmgruber Jan 4, 2024
66d91dc
Only run GM layout variations when running update
bernhardmgruber Jan 4, 2024
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77 changes: 39 additions & 38 deletions examples/alpaka/nbody/nbody.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -43,9 +43,9 @@ constexpr auto runUpdate = true; // run update step. Useful to disable for bench
#endif

#if ANY_CPU_ENABLED
constexpr auto elementsPerThread = xsimd::batch<float>::size;
constexpr auto threadsPerBlock = 1;
constexpr auto sharedElementsPerBlock = 1;
constexpr auto elementsPerThread = xsimd::batch<float>::size;
constexpr auto aosoaLanes = elementsPerThread;
#elif ANY_GPU_ENABLED
constexpr auto threadsPerBlock = 256;
Expand Down Expand Up @@ -101,9 +101,6 @@ struct llama::SimdTraits<Batch, std::enable_if_t<xsimd::is_batch<Batch>::value>>
}
};

template<typename T>
using MakeBatch = xsimd::batch<T>;

template<typename T, std::size_t N>
struct MakeSizedBatchImpl
{
Expand Down Expand Up @@ -166,66 +163,67 @@ LLAMA_FN_HOST_ACC_INLINE void pPInteraction(const Acc& acc, ParticleRefI& pis, P
pis(tag::Vel{}) += dist * sts;
}

template<int Elems, typename QuotedSMMapping>
template<int ThreadsPerBlock, int SharedElementsPerBlock, int ElementsPerThread, typename QuotedSMMapping>
struct UpdateKernel
{
// TODO(bgruber): make this an IILE in C++20
template<typename Mapping, typename Acc, std::size_t... Is>
ALPAKA_FN_HOST_ACC auto makeSharedViewHelper(const Acc& acc, std::index_sequence<Is...>) const
{
return llama::View{
Mapping{},
llama::Array<std::byte*, sizeof...(Is)>{
alpaka::declareSharedVar<std::byte[Mapping{}.blobSize(Is)], Is>(acc)...}};
}

template<typename Acc, typename View>
ALPAKA_FN_HOST_ACC void operator()(const Acc& acc, View particles) const
{
auto sharedView = [&]
{
// if there is only 1 shared element per block, use just a variable (in registers) instead of shared memory
if constexpr(sharedElementsPerBlock == 1)
if constexpr(SharedElementsPerBlock == 1)
{
using Mapping = llama::mapping::MinAlignedOne<llama::ArrayExtents<int, 1>, SharedMemoryParticle>;
return allocViewUninitialized(Mapping{}, llama::bloballoc::Array<Mapping{}.blobSize(0)>{});
}
else
{
using ArrayExtents = llama::ArrayExtents<int, sharedElementsPerBlock>;
using Mapping = typename QuotedSMMapping::template fn<ArrayExtents, SharedMemoryParticle>;
constexpr auto sharedMapping = Mapping{};

llama::Array<std::byte*, Mapping::blobCount> sharedMems{};
boost::mp11::mp_for_each<boost::mp11::mp_iota_c<Mapping::blobCount>>(
[&](auto i)
{
auto& sharedMem = alpaka::declareSharedVar<std::byte[sharedMapping.blobSize(i)], i>(acc);
sharedMems[i] = &sharedMem[0];
});
return llama::View{sharedMapping, sharedMems};
using Mapping = typename QuotedSMMapping::
template fn<llama::ArrayExtents<int, SharedElementsPerBlock>, SharedMemoryParticle>;
return makeSharedViewHelper<Mapping>(acc, std::make_index_sequence<Mapping::blobCount>{});
}
}();

const auto ti = alpaka::getIdx<alpaka::Grid, alpaka::Threads>(acc)[0];
const auto tbi = alpaka::getIdx<alpaka::Block, alpaka::Threads>(acc)[0];

auto pis = llama::SimdN<typename View::RecordDim, Elems, MakeSizedBatch>{};
llama::loadSimd(particles(ti * Elems), pis);
auto pis = llama::SimdN<Particle, ElementsPerThread, MakeSizedBatch>{};
llama::loadSimd(particles(ti * ElementsPerThread), pis);

for(int blockOffset = 0; blockOffset < problemSize; blockOffset += sharedElementsPerBlock)
for(int blockOffset = 0; blockOffset < problemSize; blockOffset += SharedElementsPerBlock)
{
for(int j = 0; j < sharedElementsPerBlock; j += threadsPerBlock)
for(int j = 0; j < SharedElementsPerBlock; j += ThreadsPerBlock)
sharedView(j) = particles(blockOffset + tbi + j);
alpaka::syncBlockThreads(acc);
for(int j = 0; j < sharedElementsPerBlock; ++j)
for(int j = 0; j < SharedElementsPerBlock; ++j)
pPInteraction(acc, pis, sharedView(j));
alpaka::syncBlockThreads(acc);
}
llama::storeSimd(pis(tag::Vel{}), particles(ti * Elems)(tag::Vel{}));
llama::storeSimd(pis(tag::Vel{}), particles(ti * ElementsPerThread)(tag::Vel{}));
}
};

template<int Elems>
template<int ElementsPerThread>
struct MoveKernel
{
template<typename Acc, typename View>
ALPAKA_FN_HOST_ACC void operator()(const Acc& acc, View particles) const
{
const auto ti = alpaka::getIdx<alpaka::Grid, alpaka::Threads>(acc)[0];
const auto i = ti * Elems;
llama::SimdN<Vec3, Elems, MakeSizedBatch> pos;
llama::SimdN<Vec3, Elems, MakeSizedBatch> vel;
const auto i = ti * ElementsPerThread;
llama::SimdN<Vec3, ElementsPerThread, MakeSizedBatch> pos;
llama::SimdN<Vec3, ElementsPerThread, MakeSizedBatch> vel;
llama::loadSimd(particles(i)(tag::Pos{}), pos);
llama::loadSimd(particles(i)(tag::Vel{}), vel);
llama::storeSimd(pos + vel * +timestep, particles(i)(tag::Pos{}));
Expand Down Expand Up @@ -354,7 +352,8 @@ void run(std::ostream& plotFile)
{
if constexpr(runUpdate)
{
auto updateKernel = UpdateKernel<elementsPerThread, QuotedMappingSM>{};
auto updateKernel
= UpdateKernel<threadsPerBlock, sharedElementsPerBlock, elementsPerThread, QuotedMappingSM>{};
alpaka::exec<Acc>(queue, workdiv, updateKernel, llama::shallowCopy(accView));
statsUpdate(watch.printAndReset("update", '\t'));
}
Expand Down Expand Up @@ -413,20 +412,22 @@ set y2tics auto
problemSize / 1024,
alpaka::getAccName<Acc>());

constexpr auto runSMVariations = hasSharedMem<Acc> && runUpdate;

run<Acc, AoS, AoS>(plotFile);
if constexpr(hasSharedMem<Acc>)
if constexpr(runSMVariations)
run<Acc, AoS, SoA_SB>(plotFile);
if constexpr(hasSharedMem<Acc>)
if constexpr(runSMVariations)
run<Acc, AoS, AoSoA>(plotFile);
run<Acc, SoA_SB, AoS>(plotFile);
if constexpr(hasSharedMem<Acc>)
run<Acc, SoA_SB, SoA_SB>(plotFile);
if constexpr(hasSharedMem<Acc>)
run<Acc, SoA_SB, AoSoA>(plotFile);
run<Acc, SoA_MB, AoS>(plotFile);
if constexpr(runSMVariations)
run<Acc, SoA_MB, SoA_SB>(plotFile);
if constexpr(runSMVariations)
run<Acc, SoA_MB, AoSoA>(plotFile);
run<Acc, AoSoA, AoS>(plotFile);
if constexpr(hasSharedMem<Acc>)
if constexpr(runSMVariations)
run<Acc, AoSoA, SoA_SB>(plotFile);
if constexpr(hasSharedMem<Acc>)
if constexpr(runSMVariations)
run<Acc, AoSoA, AoSoA>(plotFile);
run<Acc, SplitGpuGems, AoS>(plotFile);

Expand Down
3 changes: 2 additions & 1 deletion examples/common/env.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -98,9 +98,10 @@ namespace common
const auto devName = trim(getName(dev)); // TODO(bgruber): drop trim after fix lands in alpaka
const auto devProps = alpaka::getAccDevProps<Acc>(dev);
env += fmt::format(
"; alpaka acc: {}, dev[0]: {}, SMem: {}KiB",
"; alpaka acc: {}, dev[0]: {}, {}MiB GM, {}KiB SM",
accName,
devName,
alpaka::getMemBytes(dev) / 1024 / 1024,
devProps.m_sharedMemSizeBytes / 1024);
}
#endif
Expand Down
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