================
@@ -187,129 +246,56 @@ int32_t __kmpc_nvptx_teams_reduce_nowait_v2(
ThreadId = 0;
}
- uint32_t &IterCnt = state::getKernelLaunchEnvironment().ReductionIterCnt;
- uint32_t &Cnt = state::getKernelLaunchEnvironment().ReductionCnt;
-
// In non-generic mode all workers participate in the teams reduction.
// In generic mode only the team master participates in the teams
// reduction because the workers are waiting for parallel work.
uint32_t NumThreads = omp_get_num_threads();
uint32_t TeamId = omp_get_team_num();
uint32_t NumTeams = omp_get_num_teams();
- [[clang::loader_uninitialized]] static Local<unsigned> Bound;
- [[clang::loader_uninitialized]] static Local<unsigned> ChunkTeamCount;
-
- // Block progress for teams greater than the current upper
- // limit. We always only allow a number of teams less or equal
- // to the number of slots in the buffer.
- bool IsMaster = (ThreadId == 0);
- while (IsMaster) {
- Bound = atomic::load(&IterCnt, atomic::acquire);
- if (TeamId < Bound + num_of_records)
- break;
- }
- if (IsMaster) {
- int ModBockId = TeamId % num_of_records;
- if (TeamId < num_of_records) {
- lgcpyFct(GlobalBuffer, ModBockId, reduce_data);
- } else
- lgredFct(GlobalBuffer, ModBockId, reduce_data);
-
- // Propagate the memory writes above to the world.
- fence::kernel(atomic::release);
-
- // Increment team counter.
- // This counter is incremented by all teams in the current
- // num_of_records chunk.
- ChunkTeamCount = atomic::inc(&Cnt, num_of_records - 1u, atomic::seq_cst,
- atomic::MemScopeTy::device);
+ // Fast path for single-team kernels: no cross-team work required,
+ // the team-local reduction already produced the final result.
+ if (NumTeams <= 1)
+ return ThreadId == 0;
+
+ uint32_t &TeamsDone = state::getKernelLaunchEnvironment().ReductionTeamsDone;
+ void *GlobalBuffer = state::getKernelLaunchEnvironment().ReductionBuffer;
+ [[clang::loader_uninitialized]] static Local<uint32_t> TeamsDoneResult;
+
+ // Save the team's reduced value in the global buffer and atomically
+ // increment the teams-done counter.
+ if (ThreadId == 0) {
+ lgcpyFct(GlobalBuffer, TeamId, reduce_data);
+ TeamsDoneResult = atomic::inc(&TeamsDone, NumTeams - 1u, atomic::acq_rel,
+ atomic::MemScopeTy::device);
}
- // Synchronize in SPMD mode as in generic mode all but 1 threads are in the
- // state machine.
+ // This sync is needed so that all threads from last team see the shared
teams
+ // done counter value and know that they are in the last team.
if (mapping::isSPMDMode())
synchronize::threadsAligned(atomic::acq_rel);
- // reduce_data is global or shared so before being reduced within the
- // warp we need to bring it in local memory:
- // local_reduce_data = reduce_data[i]
- //
- // Example for 3 reduction variables a, b, c (of potentially different
- // types):
- //
- // buffer layout (struct of arrays):
- // a, a, ..., a, b, b, ... b, c, c, ... c
- // |__________|
- // num_of_records
- //
- // local_data_reduce layout (struct):
- // a, b, c
- //
- // Each thread will have a local struct containing the values to be
- // reduced:
- // 1. do reduction within each warp.
- // 2. do reduction across warps.
- // 3. write the final result to the main reduction variable
- // by returning 1 in the thread holding the reduction result.
-
- // Check if this is the very last team.
- unsigned NumRecs = kmpcMin(NumTeams, uint32_t(num_of_records));
- if (ChunkTeamCount == NumTeams - Bound - 1) {
- // Ensure we see the global memory writes by other teams
- fence::kernel(atomic::acquire);
-
- //
- // Last team processing.
- //
- if (ThreadId >= NumRecs)
- return 0;
- NumThreads = roundToWarpsize(kmpcMin(NumThreads, NumRecs));
- if (ThreadId >= NumThreads)
- return 0;
+ // If teams done counter reaches NumTeams-1, this is the last team.
+ if (TeamsDoneResult != NumTeams - 1u)
+ return 0;
----------------
jdoerfert wrote:
Technically, if we don't do 2 kernel reductions, we could use more than one
team if num teams is larger than num threads. But that's not important right
now.
https://github.com/llvm/llvm-project/pull/195102
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