//===---- Parallelism.cpp - OpenMP GPU parallel implementation ---- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Parallel implementation in the GPU. Here is the pattern:
//
// while (not finished) {
//
// if (master) {
// sequential code, decide which par loop to do, or if finished
// __kmpc_kernel_prepare_parallel() // exec by master only
// }
// syncthreads // A
// __kmpc_kernel_parallel() // exec by all
// if (this thread is included in the parallel) {
// switch () for all parallel loops
// __kmpc_kernel_end_parallel() // exec only by threads in parallel
// }
//
//
// The reason we don't exec end_parallel for the threads not included
// in the parallel loop is that for each barrier in the parallel
// region, these non-included threads will cycle through the
// syncthread A. Thus they must preserve their current threadId that
// is larger than thread in team.
//
// To make a long story short...
//
//===----------------------------------------------------------------------===//
#include "Debug.h"
#include "Interface.h"
#include "Mapping.h"
#include "State.h"
#include "Synchronization.h"
#include "Types.h"
#include "Utils.h"
using namespace ompx;
#pragma omp begin declare target device_type(nohost)
namespace {
uint32_t determineNumberOfThreads(int32_t NumThreadsClause) {
uint32_t NThreadsICV =
NumThreadsClause != -1 ? NumThreadsClause : icv::NThreads;
uint32_t NumThreads = mapping::getMaxTeamThreads();
if (NThreadsICV != 0 && NThreadsICV < NumThreads)
NumThreads = NThreadsICV;
// SPMD mode allows any number of threads, for generic mode we round down to a
// multiple of WARPSIZE since it is legal to do so in OpenMP.
if (mapping::isSPMDMode())
return NumThreads;
if (NumThreads < mapping::getWarpSize())
NumThreads = 1;
else
NumThreads = (NumThreads & ~((uint32_t)mapping::getWarpSize() - 1));
return NumThreads;
}
// Invoke an outlined parallel function unwrapping arguments (up to 32).
[[clang::always_inline]] void invokeMicrotask(int32_t global_tid,
int32_t bound_tid, void *fn,
void **args, int64_t nargs) {
switch (nargs) {
#include "generated_microtask_cases.gen"
default:
PRINT("Too many arguments in kmp_invoke_microtask, aborting execution.\n");
__builtin_trap();
}
}
} // namespace
extern "C" {
[[clang::always_inline]] void __kmpc_parallel_spmd(IdentTy *ident,
int32_t num_threads,
void *fn, void **args,
const int64_t nargs) {
uint32_t TId = mapping::getThreadIdInBlock();
uint32_t NumThreads = determineNumberOfThreads(num_threads);
uint32_t PTeamSize =
NumThreads == mapping::getMaxTeamThreads() ? 0 : NumThreads;
// Avoid the race between the read of the `icv::Level` above and the write
// below by synchronizing all threads here.
synchronize::threadsAligned(atomic::seq_cst);
{
// Note that the order here is important. `icv::Level` has to be updated
// last or the other updates will cause a thread specific state to be
// created.
state::ValueRAII ParallelTeamSizeRAII(state::ParallelTeamSize, PTeamSize,
1u, TId == 0, ident,
/*ForceTeamState=*/true);
state::ValueRAII ActiveLevelRAII(icv::ActiveLevel, 1u, 0u, TId == 0, ident,
/*ForceTeamState=*/true);
state::ValueRAII LevelRAII(icv::Level, 1u, 0u, TId == 0, ident,
/*ForceTeamState=*/true);
// Synchronize all threads after the main thread (TId == 0) set up the
// team state properly.
synchronize::threadsAligned(atomic::acq_rel);
state::ParallelTeamSize.assert_eq(PTeamSize, ident,
/*ForceTeamState=*/true);
icv::ActiveLevel.assert_eq(1u, ident, /*ForceTeamState=*/true);
icv::Level.assert_eq(1u, ident, /*ForceTeamState=*/true);
// Ensure we synchronize before we run user code to avoid invalidating the
// assumptions above.
synchronize::threadsAligned(atomic::relaxed);
if (!PTeamSize || TId < PTeamSize)
invokeMicrotask(TId, 0, fn, args, nargs);
// Synchronize all threads at the end of a parallel region.
synchronize::threadsAligned(atomic::seq_cst);
}
// Synchronize all threads to make sure every thread exits the scope above;
// otherwise the following assertions and the assumption in
// __kmpc_target_deinit may not hold.
synchronize::threadsAligned(atomic::acq_rel);
state::ParallelTeamSize.assert_eq(1u, ident, /*ForceTeamState=*/true);
icv::ActiveLevel.assert_eq(0u, ident, /*ForceTeamState=*/true);
icv::Level.assert_eq(0u, ident, /*ForceTeamState=*/true);
// Ensure we synchronize to create an aligned region around the assumptions.
synchronize::threadsAligned(atomic::relaxed);
return;
}
[[clang::always_inline]] void
__kmpc_parallel_51(IdentTy *ident, int32_t, int32_t if_expr,
int32_t num_threads, int proc_bind, void *fn,
void *wrapper_fn, void **args, int64_t nargs) {
uint32_t TId = mapping::getThreadIdInBlock();
// Assert the parallelism level is zero if disabled by the user.
ASSERT((config::mayUseNestedParallelism() || icv::Level == 0),
"nested parallelism while disabled");
// Handle the serialized case first, same for SPMD/non-SPMD:
// 1) if-clause(0)
// 2) parallel in task or other thread state inducing construct
// 3) nested parallel regions
if (OMP_UNLIKELY(!if_expr || state::HasThreadState ||
(config::mayUseNestedParallelism() && icv::Level))) {
state::DateEnvironmentRAII DERAII(ident);
++icv::Level;
invokeMicrotask(TId, 0, fn, args, nargs);
return;
}
// From this point forward we know that there is no thread state used.
ASSERT(state::HasThreadState == false, nullptr);
if (mapping::isSPMDMode()) {
// This was moved to its own routine so it could be called directly
// in certain situations to avoid resource consumption of unused
// logic in parallel_51.
__kmpc_parallel_spmd(ident, num_threads, fn, args, nargs);
return;
}
uint32_t NumThreads = determineNumberOfThreads(num_threads);
uint32_t MaxTeamThreads = mapping::getMaxTeamThreads();
uint32_t PTeamSize = NumThreads == MaxTeamThreads ? 0 : NumThreads;
// We do *not* create a new data environment because all threads in the team
// that are active are now running this parallel region. They share the
// TeamState, which has an increase level-var and potentially active-level
// set, but they do not have individual ThreadStates yet. If they ever
// modify the ICVs beyond this point a ThreadStates will be allocated.
bool IsActiveParallelRegion = NumThreads > 1;
if (!IsActiveParallelRegion) {
state::ValueRAII LevelRAII(icv::Level, 1u, 0u, true, ident);
invokeMicrotask(TId, 0, fn, args, nargs);
return;
}
void **GlobalArgs = nullptr;
if (nargs) {
__kmpc_begin_sharing_variables(&GlobalArgs, nargs);
switch (nargs) {
default:
for (int I = 0; I < nargs; I++)
GlobalArgs[I] = args[I];
break;
case 16:
GlobalArgs[15] = args[15];
[[fallthrough]];
case 15:
GlobalArgs[14] = args[14];
[[fallthrough]];
case 14:
GlobalArgs[13] = args[13];
[[fallthrough]];
case 13:
GlobalArgs[12] = args[12];
[[fallthrough]];
case 12:
GlobalArgs[11] = args[11];
[[fallthrough]];
case 11:
GlobalArgs[10] = args[10];
[[fallthrough]];
case 10:
GlobalArgs[9] = args[9];
[[fallthrough]];
case 9:
GlobalArgs[8] = args[8];
[[fallthrough]];
case 8:
GlobalArgs[7] = args[7];
[[fallthrough]];
case 7:
GlobalArgs[6] = args[6];
[[fallthrough]];
case 6:
GlobalArgs[5] = args[5];
[[fallthrough]];
case 5:
GlobalArgs[4] = args[4];
[[fallthrough]];
case 4:
GlobalArgs[3] = args[3];
[[fallthrough]];
case 3:
GlobalArgs[2] = args[2];
[[fallthrough]];
case 2:
GlobalArgs[1] = args[1];
[[fallthrough]];
case 1:
GlobalArgs[0] = args[0];
[[fallthrough]];
case 0:
break;
}
}
{
// Note that the order here is important. `icv::Level` has to be updated
// last or the other updates will cause a thread specific state to be
// created.
state::ValueRAII ParallelTeamSizeRAII(state::ParallelTeamSize, PTeamSize,
1u, true, ident,
/*ForceTeamState=*/true);
state::ValueRAII ParallelRegionFnRAII(state::ParallelRegionFn, wrapper_fn,
(void *)nullptr, true, ident,
/*ForceTeamState=*/true);
state::ValueRAII ActiveLevelRAII(icv::ActiveLevel, 1u, 0u, true, ident,
/*ForceTeamState=*/true);
state::ValueRAII LevelRAII(icv::Level, 1u, 0u, true, ident,
/*ForceTeamState=*/true);
// Master signals work to activate workers.
synchronize::threads(atomic::seq_cst);
// Master waits for workers to signal.
synchronize::threads(atomic::seq_cst);
}
if (nargs)
__kmpc_end_sharing_variables();
}
[[clang::noinline]] bool __kmpc_kernel_parallel(ParallelRegionFnTy *WorkFn) {
// Work function and arguments for L1 parallel region.
*WorkFn = state::ParallelRegionFn;
// If this is the termination signal from the master, quit early.
if (!*WorkFn)
return false;
// Set to true for workers participating in the parallel region.
uint32_t TId = mapping::getThreadIdInBlock();
bool ThreadIsActive = TId < state::getEffectivePTeamSize();
return ThreadIsActive;
}
[[clang::noinline]] void __kmpc_kernel_end_parallel() {
// In case we have modified an ICV for this thread before a ThreadState was
// created. We drop it now to not contaminate the next parallel region.
ASSERT(!mapping::isSPMDMode(), nullptr);
uint32_t TId = mapping::getThreadIdInBlock();
state::resetStateForThread(TId);
ASSERT(!mapping::isSPMDMode(), nullptr);
}
uint16_t __kmpc_parallel_level(IdentTy *, uint32_t) { return omp_get_level(); }
int32_t __kmpc_global_thread_num(IdentTy *) { return omp_get_thread_num(); }
void __kmpc_push_num_teams(IdentTy *loc, int32_t tid, int32_t num_teams,
int32_t thread_limit) {}
void __kmpc_push_proc_bind(IdentTy *loc, uint32_t tid, int proc_bind) {}
}
#pragma omp end declare target
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