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Fix a race condition in splitVertices #45656

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Aug 8, 2024
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Fix a race condition in splitVertices #45656

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81 changes: 33 additions & 48 deletions RecoTracker/PixelVertexFinding/plugins/alpaka/splitVertices.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,30 +19,10 @@ namespace ALPAKA_ACCELERATOR_NAMESPACE::vertexFinder {
using WsSoAView = ::vertexFinder::PixelVertexWorkSpaceSoAView;
template <typename TAcc>
ALPAKA_FN_ACC ALPAKA_FN_INLINE __attribute__((always_inline)) void splitVertices(const TAcc& acc,
VtxSoAView& pdata,
WsSoAView& pws,
VtxSoAView& data,
WsSoAView& ws,
float maxChi2) {
constexpr bool verbose = false; // in principle the compiler should optmize out if false
const uint32_t threadIdxLocal(alpaka::getIdx<alpaka::Block, alpaka::Threads>(acc)[0u]);

auto& __restrict__ data = pdata;
auto& __restrict__ ws = pws;
auto nt = ws.ntrks();
float const* __restrict__ zt = ws.zt();
float const* __restrict__ ezt2 = ws.ezt2();
float* __restrict__ zv = data.zv();
float* __restrict__ wv = data.wv();
float const* __restrict__ chi2 = data.chi2();
Comment on lines -28 to -35
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These should no longer be needed, because the SoA accessors include the __restrict__ qualifier.

uint32_t& nvFinal = data.nvFinal();

int32_t const* __restrict__ nn = data.ndof();
int32_t* __restrict__ iv = ws.iv();

ALPAKA_ASSERT_ACC(zt);
ALPAKA_ASSERT_ACC(wv);
ALPAKA_ASSERT_ACC(chi2);
ALPAKA_ASSERT_ACC(nn);
Comment on lines -41 to -44
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These are no longer needed, because the SoA View should guarantee that these are non-null.


constexpr uint32_t MAXTK = 512;

auto& it = alpaka::declareSharedVar<uint32_t[MAXTK], __COUNTER__>(acc); // track index
Expand All @@ -51,32 +31,33 @@ namespace ALPAKA_ACCELERATOR_NAMESPACE::vertexFinder {
auto& ww = alpaka::declareSharedVar<float[MAXTK], __COUNTER__>(acc); // z weight
auto& nq = alpaka::declareSharedVar<uint32_t, __COUNTER__>(acc); // number of track for this vertex

const uint32_t blockIdx(alpaka::getIdx<alpaka::Grid, alpaka::Blocks>(acc)[0u]);
const uint32_t gridDimension(alpaka::getWorkDiv<alpaka::Grid, alpaka::Blocks>(acc)[0u]);

// one vertex per block
for (auto kv = blockIdx; kv < nvFinal; kv += gridDimension) {
if (nn[kv] < 4)
for (auto kv : cms::alpakatools::independent_groups(acc, data.nvFinal())) {
int32_t ndof = data[kv].ndof();
if (ndof < 4)
continue;
if (chi2[kv] < maxChi2 * float(nn[kv]))
if (data[kv].chi2() < maxChi2 * float(ndof))
continue;

ALPAKA_ASSERT_ACC(nn[kv] < int32_t(MAXTK));
ALPAKA_ASSERT_ACC(ndof < int32_t(MAXTK));

if ((uint32_t)nn[kv] >= MAXTK)
if ((uint32_t)ndof >= MAXTK)
continue; // too bad FIXME

nq = 0u;
if (cms::alpakatools::once_per_block(acc)) {
// reset the number of tracks for the current vertex
nq = 0u;
}
alpaka::syncBlockThreads(acc);

// copy to local
for (auto k : cms::alpakatools::independent_group_elements(acc, nt)) {
if (iv[k] == int(kv)) {
auto old = alpaka::atomicInc(acc, &nq, MAXTK, alpaka::hierarchy::Threads{});
zz[old] = zt[k] - zv[kv];
newV[old] = zz[old] < 0 ? 0 : 1;
ww[old] = 1.f / ezt2[k];
it[old] = k;
// cache the data of the tracks associated to the current vertex into shared memory
for (auto k : cms::alpakatools::independent_group_elements(acc, ws.ntrks())) {
if (ws[k].iv() == int(kv)) {
auto index = alpaka::atomicInc(acc, &nq, MAXTK, alpaka::hierarchy::Threads{});
it[index] = k;
zz[index] = ws[k].zt() - data[kv].zv();
newV[index] = zz[index] < 0 ? 0 : 1;
ww[index] = 1.f / ws[k].ezt2();
}
}

Expand All @@ -85,14 +66,14 @@ namespace ALPAKA_ACCELERATOR_NAMESPACE::vertexFinder {
auto& wnew = alpaka::declareSharedVar<float[2], __COUNTER__>(acc);
alpaka::syncBlockThreads(acc);

ALPAKA_ASSERT_ACC(int(nq) == nn[kv] + 1);
ALPAKA_ASSERT_ACC(int(nq) == ndof + 1);

int maxiter = 20;
// kt-min....
bool more = true;
while (alpaka::syncBlockThreadsPredicate<alpaka::BlockOr>(acc, more)) {
more = false;
if (0 == threadIdxLocal) {
if (cms::alpakatools::once_per_block(acc)) {
znew[0] = 0;
znew[1] = 0;
wnew[0] = 0;
Expand All @@ -107,7 +88,7 @@ namespace ALPAKA_ACCELERATOR_NAMESPACE::vertexFinder {
}
alpaka::syncBlockThreads(acc);

if (0 == threadIdxLocal) {
if (cms::alpakatools::once_per_block(acc)) {
znew[0] /= wnew[0];
znew[1] /= wnew[1];
}
Expand All @@ -134,30 +115,34 @@ namespace ALPAKA_ACCELERATOR_NAMESPACE::vertexFinder {

auto chi2Dist = dist2 / (1.f / wnew[0] + 1.f / wnew[1]);

if (verbose && 0 == threadIdxLocal)
printf("inter %d %f %f\n", 20 - maxiter, chi2Dist, dist2 * wv[kv]);
if constexpr (verbose) {
if (cms::alpakatools::once_per_block(acc))
printf("inter %d %f %f\n", 20 - maxiter, chi2Dist, dist2 * data[kv].wv());
}

if (chi2Dist < 4)
continue;

// get a new global vertex
auto& igv = alpaka::declareSharedVar<uint32_t, __COUNTER__>(acc);
if (0 == threadIdxLocal)
if (cms::alpakatools::once_per_block(acc))
igv = alpaka::atomicAdd(acc, &ws.nvIntermediate(), 1u, alpaka::hierarchy::Blocks{});
alpaka::syncBlockThreads(acc);
for (auto k : cms::alpakatools::uniform_elements(acc, nq)) {
if (1 == newV[k])
iv[it[k]] = igv;
ws[it[k]].iv() = igv;
}

// synchronise the threads before starting the next iteration of the loop over the vertices and resetting the shared memory
alpaka::syncBlockThreads(acc);
} // loop on vertices
}

class SplitVerticesKernel {
public:
template <typename TAcc>
ALPAKA_FN_ACC void operator()(const TAcc& acc, VtxSoAView pdata, WsSoAView pws, float maxChi2) const {
splitVertices(acc, pdata, pws, maxChi2);
ALPAKA_FN_ACC void operator()(const TAcc& acc, VtxSoAView data, WsSoAView ws, float maxChi2) const {
splitVertices(acc, data, ws, maxChi2);
}
};

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