| //===- AsyncParallelFor.cpp - Implementation of Async Parallel For --------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements scf.parallel to scf.for + async.execute conversion pass. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "PassDetail.h" |
| #include "mlir/Dialect/Arithmetic/IR/Arithmetic.h" |
| #include "mlir/Dialect/Async/IR/Async.h" |
| #include "mlir/Dialect/Async/Passes.h" |
| #include "mlir/Dialect/SCF/SCF.h" |
| #include "mlir/Dialect/StandardOps/IR/Ops.h" |
| #include "mlir/IR/BlockAndValueMapping.h" |
| #include "mlir/IR/ImplicitLocOpBuilder.h" |
| #include "mlir/IR/PatternMatch.h" |
| #include "mlir/Transforms/GreedyPatternRewriteDriver.h" |
| #include "mlir/Transforms/RegionUtils.h" |
| |
| using namespace mlir; |
| using namespace mlir::async; |
| |
| #define DEBUG_TYPE "async-parallel-for" |
| |
| namespace { |
| |
| // Rewrite scf.parallel operation into multiple concurrent async.execute |
| // operations over non overlapping subranges of the original loop. |
| // |
| // Example: |
| // |
| // scf.parallel (%i, %j) = (%lbi, %lbj) to (%ubi, %ubj) step (%si, %sj) { |
| // "do_some_compute"(%i, %j): () -> () |
| // } |
| // |
| // Converted to: |
| // |
| // // Parallel compute function that executes the parallel body region for |
| // // a subset of the parallel iteration space defined by the one-dimensional |
| // // compute block index. |
| // func parallel_compute_function(%block_index : index, %block_size : index, |
| // <parallel operation properties>, ...) { |
| // // Compute multi-dimensional loop bounds for %block_index. |
| // %block_lbi, %block_lbj = ... |
| // %block_ubi, %block_ubj = ... |
| // |
| // // Clone parallel operation body into the scf.for loop nest. |
| // scf.for %i = %blockLbi to %blockUbi { |
| // scf.for %j = block_lbj to %block_ubj { |
| // "do_some_compute"(%i, %j): () -> () |
| // } |
| // } |
| // } |
| // |
| // And a dispatch function depending on the `asyncDispatch` option. |
| // |
| // When async dispatch is on: (pseudocode) |
| // |
| // %block_size = ... compute parallel compute block size |
| // %block_count = ... compute the number of compute blocks |
| // |
| // func @async_dispatch(%block_start : index, %block_end : index, ...) { |
| // // Keep splitting block range until we reached a range of size 1. |
| // while (%block_end - %block_start > 1) { |
| // %mid_index = block_start + (block_end - block_start) / 2; |
| // async.execute { call @async_dispatch(%mid_index, %block_end); } |
| // %block_end = %mid_index |
| // } |
| // |
| // // Call parallel compute function for a single block. |
| // call @parallel_compute_fn(%block_start, %block_size, ...); |
| // } |
| // |
| // // Launch async dispatch for [0, block_count) range. |
| // call @async_dispatch(%c0, %block_count); |
| // |
| // When async dispatch is off: |
| // |
| // %block_size = ... compute parallel compute block size |
| // %block_count = ... compute the number of compute blocks |
| // |
| // scf.for %block_index = %c0 to %block_count { |
| // call @parallel_compute_fn(%block_index, %block_size, ...) |
| // } |
| // |
| struct AsyncParallelForPass |
| : public AsyncParallelForBase<AsyncParallelForPass> { |
| AsyncParallelForPass() = default; |
| |
| AsyncParallelForPass(bool asyncDispatch, int32_t numWorkerThreads, |
| int32_t minTaskSize) { |
| this->asyncDispatch = asyncDispatch; |
| this->numWorkerThreads = numWorkerThreads; |
| this->minTaskSize = minTaskSize; |
| } |
| |
| void runOnOperation() override; |
| }; |
| |
| struct AsyncParallelForRewrite : public OpRewritePattern<scf::ParallelOp> { |
| public: |
| AsyncParallelForRewrite(MLIRContext *ctx, bool asyncDispatch, |
| int32_t numWorkerThreads, int32_t minTaskSize) |
| : OpRewritePattern(ctx), asyncDispatch(asyncDispatch), |
| numWorkerThreads(numWorkerThreads), minTaskSize(minTaskSize) {} |
| |
| LogicalResult matchAndRewrite(scf::ParallelOp op, |
| PatternRewriter &rewriter) const override; |
| |
| private: |
| bool asyncDispatch; |
| int32_t numWorkerThreads; |
| int32_t minTaskSize; |
| }; |
| |
| struct ParallelComputeFunctionType { |
| FunctionType type; |
| llvm::SmallVector<Value> captures; |
| }; |
| |
| struct ParallelComputeFunction { |
| FuncOp func; |
| llvm::SmallVector<Value> captures; |
| }; |
| |
| } // namespace |
| |
| // Converts one-dimensional iteration index in the [0, tripCount) interval |
| // into multidimensional iteration coordinate. |
| static SmallVector<Value> delinearize(ImplicitLocOpBuilder &b, Value index, |
| ArrayRef<Value> tripCounts) { |
| SmallVector<Value> coords(tripCounts.size()); |
| assert(!tripCounts.empty() && "tripCounts must be not empty"); |
| |
| for (ssize_t i = tripCounts.size() - 1; i >= 0; --i) { |
| coords[i] = b.create<arith::RemSIOp>(index, tripCounts[i]); |
| index = b.create<arith::DivSIOp>(index, tripCounts[i]); |
| } |
| |
| return coords; |
| } |
| |
| // Returns a function type and implicit captures for a parallel compute |
| // function. We'll need a list of implicit captures to setup block and value |
| // mapping when we'll clone the body of the parallel operation. |
| static ParallelComputeFunctionType |
| getParallelComputeFunctionType(scf::ParallelOp op, PatternRewriter &rewriter) { |
| // Values implicitly captured by the parallel operation. |
| llvm::SetVector<Value> captures; |
| getUsedValuesDefinedAbove(op.region(), op.region(), captures); |
| |
| llvm::SmallVector<Type> inputs; |
| inputs.reserve(2 + 4 * op.getNumLoops() + captures.size()); |
| |
| Type indexTy = rewriter.getIndexType(); |
| |
| // One-dimensional iteration space defined by the block index and size. |
| inputs.push_back(indexTy); // blockIndex |
| inputs.push_back(indexTy); // blockSize |
| |
| // Multi-dimensional parallel iteration space defined by the loop trip counts. |
| for (unsigned i = 0; i < op.getNumLoops(); ++i) |
| inputs.push_back(indexTy); // loop tripCount |
| |
| // Parallel operation lower bound, upper bound and step. |
| for (unsigned i = 0; i < op.getNumLoops(); ++i) { |
| inputs.push_back(indexTy); // lower bound |
| inputs.push_back(indexTy); // upper bound |
| inputs.push_back(indexTy); // step |
| } |
| |
| // Types of the implicit captures. |
| for (Value capture : captures) |
| inputs.push_back(capture.getType()); |
| |
| // Convert captures to vector for later convenience. |
| SmallVector<Value> capturesVector(captures.begin(), captures.end()); |
| return {rewriter.getFunctionType(inputs, TypeRange()), capturesVector}; |
| } |
| |
| // Create a parallel compute fuction from the parallel operation. |
| static ParallelComputeFunction |
| createParallelComputeFunction(scf::ParallelOp op, PatternRewriter &rewriter) { |
| OpBuilder::InsertionGuard guard(rewriter); |
| ImplicitLocOpBuilder b(op.getLoc(), rewriter); |
| |
| ModuleOp module = op->getParentOfType<ModuleOp>(); |
| |
| // Make sure that all constants will be inside the parallel operation body to |
| // reduce the number of parallel compute function arguments. |
| cloneConstantsIntoTheRegion(op.getLoopBody(), rewriter); |
| |
| ParallelComputeFunctionType computeFuncType = |
| getParallelComputeFunctionType(op, rewriter); |
| |
| FunctionType type = computeFuncType.type; |
| FuncOp func = FuncOp::create(op.getLoc(), "parallel_compute_fn", type); |
| func.setPrivate(); |
| |
| // Insert function into the module symbol table and assign it unique name. |
| SymbolTable symbolTable(module); |
| symbolTable.insert(func); |
| rewriter.getListener()->notifyOperationInserted(func); |
| |
| // Create function entry block. |
| Block *block = b.createBlock(&func.getBody(), func.begin(), type.getInputs()); |
| b.setInsertionPointToEnd(block); |
| |
| unsigned offset = 0; // argument offset for arguments decoding |
| |
| // Returns `numArguments` arguments starting from `offset` and updates offset |
| // by moving forward to the next argument. |
| auto getArguments = [&](unsigned numArguments) -> ArrayRef<Value> { |
| auto args = block->getArguments(); |
| auto slice = args.drop_front(offset).take_front(numArguments); |
| offset += numArguments; |
| return {slice.begin(), slice.end()}; |
| }; |
| |
| // Block iteration position defined by the block index and size. |
| Value blockIndex = block->getArgument(offset++); |
| Value blockSize = block->getArgument(offset++); |
| |
| // Constants used below. |
| Value c0 = b.create<arith::ConstantIndexOp>(0); |
| Value c1 = b.create<arith::ConstantIndexOp>(1); |
| |
| // Multi-dimensional parallel iteration space defined by the loop trip counts. |
| ArrayRef<Value> tripCounts = getArguments(op.getNumLoops()); |
| |
| // Compute a product of trip counts to get the size of the flattened |
| // one-dimensional iteration space. |
| Value tripCount = tripCounts[0]; |
| for (unsigned i = 1; i < tripCounts.size(); ++i) |
| tripCount = b.create<arith::MulIOp>(tripCount, tripCounts[i]); |
| |
| // Parallel operation lower bound and step. |
| ArrayRef<Value> lowerBound = getArguments(op.getNumLoops()); |
| offset += op.getNumLoops(); // skip upper bound arguments |
| ArrayRef<Value> step = getArguments(op.getNumLoops()); |
| |
| // Remaining arguments are implicit captures of the parallel operation. |
| ArrayRef<Value> captures = getArguments(block->getNumArguments() - offset); |
| |
| // Find one-dimensional iteration bounds: [blockFirstIndex, blockLastIndex]: |
| // blockFirstIndex = blockIndex * blockSize |
| Value blockFirstIndex = b.create<arith::MulIOp>(blockIndex, blockSize); |
| |
| // The last one-dimensional index in the block defined by the `blockIndex`: |
| Value blockEnd0 = b.create<arith::AddIOp>(blockFirstIndex, blockSize); |
| Value blockEnd1 = b.create<arith::MinSIOp>(blockEnd0, tripCount); |
| Value blockLastIndex = b.create<arith::SubIOp>(blockEnd1, c1); |
| |
| // Convert one-dimensional indices to multi-dimensional coordinates. |
| auto blockFirstCoord = delinearize(b, blockFirstIndex, tripCounts); |
| auto blockLastCoord = delinearize(b, blockLastIndex, tripCounts); |
| |
| // Compute loops upper bounds derived from the block last coordinates: |
| // blockEndCoord[i] = blockLastCoord[i] + 1 |
| // |
| // Block first and last coordinates can be the same along the outer compute |
| // dimension when inner compute dimension contains multiple blocks. |
| SmallVector<Value> blockEndCoord(op.getNumLoops()); |
| for (size_t i = 0; i < blockLastCoord.size(); ++i) |
| blockEndCoord[i] = b.create<arith::AddIOp>(blockLastCoord[i], c1); |
| |
| // Construct a loop nest out of scf.for operations that will iterate over |
| // all coordinates in [blockFirstCoord, blockLastCoord] range. |
| using LoopBodyBuilder = |
| std::function<void(OpBuilder &, Location, Value, ValueRange)>; |
| using LoopNestBuilder = std::function<LoopBodyBuilder(size_t loopIdx)>; |
| |
| // Parallel region induction variables computed from the multi-dimensional |
| // iteration coordinate using parallel operation bounds and step: |
| // |
| // computeBlockInductionVars[loopIdx] = |
| // lowerBound[loopIdx] + blockCoord[loopIdx] * step[loopDdx] |
| SmallVector<Value> computeBlockInductionVars(op.getNumLoops()); |
| |
| // We need to know if we are in the first or last iteration of the |
| // multi-dimensional loop for each loop in the nest, so we can decide what |
| // loop bounds should we use for the nested loops: bounds defined by compute |
| // block interval, or bounds defined by the parallel operation. |
| // |
| // Example: 2d parallel operation |
| // i j |
| // loop sizes: [50, 50] |
| // first coord: [25, 25] |
| // last coord: [30, 30] |
| // |
| // If `i` is equal to 25 then iteration over `j` should start at 25, when `i` |
| // is between 25 and 30 it should start at 0. The upper bound for `j` should |
| // be 50, except when `i` is equal to 30, then it should also be 30. |
| // |
| // Value at ith position specifies if all loops in [0, i) range of the loop |
| // nest are in the first/last iteration. |
| SmallVector<Value> isBlockFirstCoord(op.getNumLoops()); |
| SmallVector<Value> isBlockLastCoord(op.getNumLoops()); |
| |
| // Builds inner loop nest inside async.execute operation that does all the |
| // work concurrently. |
| LoopNestBuilder workLoopBuilder = [&](size_t loopIdx) -> LoopBodyBuilder { |
| return [&, loopIdx](OpBuilder &nestedBuilder, Location loc, Value iv, |
| ValueRange args) { |
| ImplicitLocOpBuilder nb(loc, nestedBuilder); |
| |
| // Compute induction variable for `loopIdx`. |
| computeBlockInductionVars[loopIdx] = nb.create<arith::AddIOp>( |
| lowerBound[loopIdx], nb.create<arith::MulIOp>(iv, step[loopIdx])); |
| |
| // Check if we are inside first or last iteration of the loop. |
| isBlockFirstCoord[loopIdx] = nb.create<arith::CmpIOp>( |
| arith::CmpIPredicate::eq, iv, blockFirstCoord[loopIdx]); |
| isBlockLastCoord[loopIdx] = nb.create<arith::CmpIOp>( |
| arith::CmpIPredicate::eq, iv, blockLastCoord[loopIdx]); |
| |
| // Check if the previous loop is in its first or last iteration. |
| if (loopIdx > 0) { |
| isBlockFirstCoord[loopIdx] = nb.create<arith::AndIOp>( |
| isBlockFirstCoord[loopIdx], isBlockFirstCoord[loopIdx - 1]); |
| isBlockLastCoord[loopIdx] = nb.create<arith::AndIOp>( |
| isBlockLastCoord[loopIdx], isBlockLastCoord[loopIdx - 1]); |
| } |
| |
| // Keep building loop nest. |
| if (loopIdx < op.getNumLoops() - 1) { |
| // Select nested loop lower/upper bounds depending on out position in |
| // the multi-dimensional iteration space. |
| auto lb = nb.create<SelectOp>(isBlockFirstCoord[loopIdx], |
| blockFirstCoord[loopIdx + 1], c0); |
| |
| auto ub = nb.create<SelectOp>(isBlockLastCoord[loopIdx], |
| blockEndCoord[loopIdx + 1], |
| tripCounts[loopIdx + 1]); |
| |
| nb.create<scf::ForOp>(lb, ub, c1, ValueRange(), |
| workLoopBuilder(loopIdx + 1)); |
| nb.create<scf::YieldOp>(loc); |
| return; |
| } |
| |
| // Copy the body of the parallel op into the inner-most loop. |
| BlockAndValueMapping mapping; |
| mapping.map(op.getInductionVars(), computeBlockInductionVars); |
| mapping.map(computeFuncType.captures, captures); |
| |
| for (auto &bodyOp : op.getLoopBody().getOps()) |
| nb.clone(bodyOp, mapping); |
| }; |
| }; |
| |
| b.create<scf::ForOp>(blockFirstCoord[0], blockEndCoord[0], c1, ValueRange(), |
| workLoopBuilder(0)); |
| b.create<ReturnOp>(ValueRange()); |
| |
| return {func, std::move(computeFuncType.captures)}; |
| } |
| |
| // Creates recursive async dispatch function for the given parallel compute |
| // function. Dispatch function keeps splitting block range into halves until it |
| // reaches a single block, and then excecutes it inline. |
| // |
| // Function pseudocode (mix of C++ and MLIR): |
| // |
| // func @async_dispatch(%block_start : index, %block_end : index, ...) { |
| // |
| // // Keep splitting block range until we reached a range of size 1. |
| // while (%block_end - %block_start > 1) { |
| // %mid_index = block_start + (block_end - block_start) / 2; |
| // async.execute { call @async_dispatch(%mid_index, %block_end); } |
| // %block_end = %mid_index |
| // } |
| // |
| // // Call parallel compute function for a single block. |
| // call @parallel_compute_fn(%block_start, %block_size, ...); |
| // } |
| // |
| static FuncOp createAsyncDispatchFunction(ParallelComputeFunction &computeFunc, |
| PatternRewriter &rewriter) { |
| OpBuilder::InsertionGuard guard(rewriter); |
| Location loc = computeFunc.func.getLoc(); |
| ImplicitLocOpBuilder b(loc, rewriter); |
| |
| ModuleOp module = computeFunc.func->getParentOfType<ModuleOp>(); |
| |
| ArrayRef<Type> computeFuncInputTypes = |
| computeFunc.func.type().cast<FunctionType>().getInputs(); |
| |
| // Compared to the parallel compute function async dispatch function takes |
| // additional !async.group argument. Also instead of a single `blockIndex` it |
| // takes `blockStart` and `blockEnd` arguments to define the range of |
| // dispatched blocks. |
| SmallVector<Type> inputTypes; |
| inputTypes.push_back(async::GroupType::get(rewriter.getContext())); |
| inputTypes.push_back(rewriter.getIndexType()); // add blockStart argument |
| inputTypes.append(computeFuncInputTypes.begin(), computeFuncInputTypes.end()); |
| |
| FunctionType type = rewriter.getFunctionType(inputTypes, TypeRange()); |
| FuncOp func = FuncOp::create(loc, "async_dispatch_fn", type); |
| func.setPrivate(); |
| |
| // Insert function into the module symbol table and assign it unique name. |
| SymbolTable symbolTable(module); |
| symbolTable.insert(func); |
| rewriter.getListener()->notifyOperationInserted(func); |
| |
| // Create function entry block. |
| Block *block = b.createBlock(&func.getBody(), func.begin(), type.getInputs()); |
| b.setInsertionPointToEnd(block); |
| |
| Type indexTy = b.getIndexType(); |
| Value c1 = b.create<arith::ConstantIndexOp>(1); |
| Value c2 = b.create<arith::ConstantIndexOp>(2); |
| |
| // Get the async group that will track async dispatch completion. |
| Value group = block->getArgument(0); |
| |
| // Get the block iteration range: [blockStart, blockEnd) |
| Value blockStart = block->getArgument(1); |
| Value blockEnd = block->getArgument(2); |
| |
| // Create a work splitting while loop for the [blockStart, blockEnd) range. |
| SmallVector<Type> types = {indexTy, indexTy}; |
| SmallVector<Value> operands = {blockStart, blockEnd}; |
| |
| // Create a recursive dispatch loop. |
| scf::WhileOp whileOp = b.create<scf::WhileOp>(types, operands); |
| Block *before = b.createBlock(&whileOp.before(), {}, types); |
| Block *after = b.createBlock(&whileOp.after(), {}, types); |
| |
| // Setup dispatch loop condition block: decide if we need to go into the |
| // `after` block and launch one more async dispatch. |
| { |
| b.setInsertionPointToEnd(before); |
| Value start = before->getArgument(0); |
| Value end = before->getArgument(1); |
| Value distance = b.create<arith::SubIOp>(end, start); |
| Value dispatch = |
| b.create<arith::CmpIOp>(arith::CmpIPredicate::sgt, distance, c1); |
| b.create<scf::ConditionOp>(dispatch, before->getArguments()); |
| } |
| |
| // Setup the async dispatch loop body: recursively call dispatch function |
| // for the seconds half of the original range and go to the next iteration. |
| { |
| b.setInsertionPointToEnd(after); |
| Value start = after->getArgument(0); |
| Value end = after->getArgument(1); |
| Value distance = b.create<arith::SubIOp>(end, start); |
| Value halfDistance = b.create<arith::DivSIOp>(distance, c2); |
| Value midIndex = b.create<arith::AddIOp>(start, halfDistance); |
| |
| // Call parallel compute function inside the async.execute region. |
| auto executeBodyBuilder = [&](OpBuilder &executeBuilder, |
| Location executeLoc, ValueRange executeArgs) { |
| // Update the original `blockStart` and `blockEnd` with new range. |
| SmallVector<Value> operands{block->getArguments().begin(), |
| block->getArguments().end()}; |
| operands[1] = midIndex; |
| operands[2] = end; |
| |
| executeBuilder.create<CallOp>(executeLoc, func.sym_name(), |
| func.getCallableResults(), operands); |
| executeBuilder.create<async::YieldOp>(executeLoc, ValueRange()); |
| }; |
| |
| // Create async.execute operation to dispatch half of the block range. |
| auto execute = b.create<ExecuteOp>(TypeRange(), ValueRange(), ValueRange(), |
| executeBodyBuilder); |
| b.create<AddToGroupOp>(indexTy, execute.token(), group); |
| b.create<scf::YieldOp>(ValueRange({start, midIndex})); |
| } |
| |
| // After dispatching async operations to process the tail of the block range |
| // call the parallel compute function for the first block of the range. |
| b.setInsertionPointAfter(whileOp); |
| |
| // Drop async dispatch specific arguments: async group, block start and end. |
| auto forwardedInputs = block->getArguments().drop_front(3); |
| SmallVector<Value> computeFuncOperands = {blockStart}; |
| computeFuncOperands.append(forwardedInputs.begin(), forwardedInputs.end()); |
| |
| b.create<CallOp>(computeFunc.func.sym_name(), |
| computeFunc.func.getCallableResults(), computeFuncOperands); |
| b.create<ReturnOp>(ValueRange()); |
| |
| return func; |
| } |
| |
| // Launch async dispatch of the parallel compute function. |
| static void doAsyncDispatch(ImplicitLocOpBuilder &b, PatternRewriter &rewriter, |
| ParallelComputeFunction ¶llelComputeFunction, |
| scf::ParallelOp op, Value blockSize, |
| Value blockCount, |
| const SmallVector<Value> &tripCounts) { |
| MLIRContext *ctx = op->getContext(); |
| |
| // Add one more level of indirection to dispatch parallel compute functions |
| // using async operations and recursive work splitting. |
| FuncOp asyncDispatchFunction = |
| createAsyncDispatchFunction(parallelComputeFunction, rewriter); |
| |
| Value c0 = b.create<arith::ConstantIndexOp>(0); |
| Value c1 = b.create<arith::ConstantIndexOp>(1); |
| |
| // Appends operands shared by async dispatch and parallel compute functions to |
| // the given operands vector. |
| auto appendBlockComputeOperands = [&](SmallVector<Value> &operands) { |
| operands.append(tripCounts); |
| operands.append(op.lowerBound().begin(), op.lowerBound().end()); |
| operands.append(op.upperBound().begin(), op.upperBound().end()); |
| operands.append(op.step().begin(), op.step().end()); |
| operands.append(parallelComputeFunction.captures); |
| }; |
| |
| // Check if the block size is one, in this case we can skip the async dispatch |
| // completely. If this will be known statically, then canonicalization will |
| // erase async group operations. |
| Value isSingleBlock = |
| b.create<arith::CmpIOp>(arith::CmpIPredicate::eq, blockCount, c1); |
| |
| auto syncDispatch = [&](OpBuilder &nestedBuilder, Location loc) { |
| ImplicitLocOpBuilder nb(loc, nestedBuilder); |
| |
| // Call parallel compute function for the single block. |
| SmallVector<Value> operands = {c0, blockSize}; |
| appendBlockComputeOperands(operands); |
| |
| nb.create<CallOp>(parallelComputeFunction.func.sym_name(), |
| parallelComputeFunction.func.getCallableResults(), |
| operands); |
| nb.create<scf::YieldOp>(); |
| }; |
| |
| auto asyncDispatch = [&](OpBuilder &nestedBuilder, Location loc) { |
| // Create an async.group to wait on all async tokens from the concurrent |
| // execution of multiple parallel compute function. First block will be |
| // executed synchronously in the caller thread. |
| Value groupSize = b.create<arith::SubIOp>(blockCount, c1); |
| Value group = b.create<CreateGroupOp>(GroupType::get(ctx), groupSize); |
| |
| ImplicitLocOpBuilder nb(loc, nestedBuilder); |
| |
| // Launch async dispatch function for [0, blockCount) range. |
| SmallVector<Value> operands = {group, c0, blockCount, blockSize}; |
| appendBlockComputeOperands(operands); |
| |
| nb.create<CallOp>(asyncDispatchFunction.sym_name(), |
| asyncDispatchFunction.getCallableResults(), operands); |
| |
| // Wait for the completion of all parallel compute operations. |
| b.create<AwaitAllOp>(group); |
| |
| nb.create<scf::YieldOp>(); |
| }; |
| |
| // Dispatch either single block compute function, or launch async dispatch. |
| b.create<scf::IfOp>(TypeRange(), isSingleBlock, syncDispatch, asyncDispatch); |
| } |
| |
| // Dispatch parallel compute functions by submitting all async compute tasks |
| // from a simple for loop in the caller thread. |
| static void |
| doSequentialDispatch(ImplicitLocOpBuilder &b, PatternRewriter &rewriter, |
| ParallelComputeFunction ¶llelComputeFunction, |
| scf::ParallelOp op, Value blockSize, Value blockCount, |
| const SmallVector<Value> &tripCounts) { |
| MLIRContext *ctx = op->getContext(); |
| |
| FuncOp compute = parallelComputeFunction.func; |
| |
| Value c0 = b.create<arith::ConstantIndexOp>(0); |
| Value c1 = b.create<arith::ConstantIndexOp>(1); |
| |
| // Create an async.group to wait on all async tokens from the concurrent |
| // execution of multiple parallel compute function. First block will be |
| // executed synchronously in the caller thread. |
| Value groupSize = b.create<arith::SubIOp>(blockCount, c1); |
| Value group = b.create<CreateGroupOp>(GroupType::get(ctx), groupSize); |
| |
| // Call parallel compute function for all blocks. |
| using LoopBodyBuilder = |
| std::function<void(OpBuilder &, Location, Value, ValueRange)>; |
| |
| // Returns parallel compute function operands to process the given block. |
| auto computeFuncOperands = [&](Value blockIndex) -> SmallVector<Value> { |
| SmallVector<Value> computeFuncOperands = {blockIndex, blockSize}; |
| computeFuncOperands.append(tripCounts); |
| computeFuncOperands.append(op.lowerBound().begin(), op.lowerBound().end()); |
| computeFuncOperands.append(op.upperBound().begin(), op.upperBound().end()); |
| computeFuncOperands.append(op.step().begin(), op.step().end()); |
| computeFuncOperands.append(parallelComputeFunction.captures); |
| return computeFuncOperands; |
| }; |
| |
| // Induction variable is the index of the block: [0, blockCount). |
| LoopBodyBuilder loopBuilder = [&](OpBuilder &loopBuilder, Location loc, |
| Value iv, ValueRange args) { |
| ImplicitLocOpBuilder nb(loc, loopBuilder); |
| |
| // Call parallel compute function inside the async.execute region. |
| auto executeBodyBuilder = [&](OpBuilder &executeBuilder, |
| Location executeLoc, ValueRange executeArgs) { |
| executeBuilder.create<CallOp>(executeLoc, compute.sym_name(), |
| compute.getCallableResults(), |
| computeFuncOperands(iv)); |
| executeBuilder.create<async::YieldOp>(executeLoc, ValueRange()); |
| }; |
| |
| // Create async.execute operation to launch parallel computate function. |
| auto execute = nb.create<ExecuteOp>(TypeRange(), ValueRange(), ValueRange(), |
| executeBodyBuilder); |
| nb.create<AddToGroupOp>(rewriter.getIndexType(), execute.token(), group); |
| nb.create<scf::YieldOp>(); |
| }; |
| |
| // Iterate over all compute blocks and launch parallel compute operations. |
| b.create<scf::ForOp>(c1, blockCount, c1, ValueRange(), loopBuilder); |
| |
| // Call parallel compute function for the first block in the caller thread. |
| b.create<CallOp>(compute.sym_name(), compute.getCallableResults(), |
| computeFuncOperands(c0)); |
| |
| // Wait for the completion of all async compute operations. |
| b.create<AwaitAllOp>(group); |
| } |
| |
| LogicalResult |
| AsyncParallelForRewrite::matchAndRewrite(scf::ParallelOp op, |
| PatternRewriter &rewriter) const { |
| // We do not currently support rewrite for parallel op with reductions. |
| if (op.getNumReductions() != 0) |
| return failure(); |
| |
| ImplicitLocOpBuilder b(op.getLoc(), rewriter); |
| |
| // Compute trip count for each loop induction variable: |
| // tripCount = ceil_div(upperBound - lowerBound, step); |
| SmallVector<Value> tripCounts(op.getNumLoops()); |
| for (size_t i = 0; i < op.getNumLoops(); ++i) { |
| auto lb = op.lowerBound()[i]; |
| auto ub = op.upperBound()[i]; |
| auto step = op.step()[i]; |
| auto range = b.create<arith::SubIOp>(ub, lb); |
| tripCounts[i] = b.create<arith::CeilDivSIOp>(range, step); |
| } |
| |
| // Compute a product of trip counts to get the 1-dimensional iteration space |
| // for the scf.parallel operation. |
| Value tripCount = tripCounts[0]; |
| for (size_t i = 1; i < tripCounts.size(); ++i) |
| tripCount = b.create<arith::MulIOp>(tripCount, tripCounts[i]); |
| |
| // Short circuit no-op parallel loops (zero iterations) that can arise from |
| // the memrefs with dynamic dimension(s) equal to zero. |
| Value c0 = b.create<arith::ConstantIndexOp>(0); |
| Value isZeroIterations = |
| b.create<arith::CmpIOp>(arith::CmpIPredicate::eq, tripCount, c0); |
| |
| // Do absolutely nothing if the trip count is zero. |
| auto noOp = [&](OpBuilder &nestedBuilder, Location loc) { |
| nestedBuilder.create<scf::YieldOp>(loc); |
| }; |
| |
| // Compute the parallel block size and dispatch concurrent tasks computing |
| // results for each block. |
| auto dispatch = [&](OpBuilder &nestedBuilder, Location loc) { |
| ImplicitLocOpBuilder nb(loc, nestedBuilder); |
| |
| // With large number of threads the value of creating many compute blocks |
| // is reduced because the problem typically becomes memory bound. For small |
| // number of threads it helps with stragglers. |
| float overshardingFactor = numWorkerThreads <= 4 ? 8.0 |
| : numWorkerThreads <= 8 ? 4.0 |
| : numWorkerThreads <= 16 ? 2.0 |
| : numWorkerThreads <= 32 ? 1.0 |
| : numWorkerThreads <= 64 ? 0.8 |
| : 0.6; |
| |
| // Do not overload worker threads with too many compute blocks. |
| Value maxComputeBlocks = b.create<arith::ConstantIndexOp>( |
| std::max(1, static_cast<int>(numWorkerThreads * overshardingFactor))); |
| |
| // Target block size from the pass parameters. |
| Value minTaskSizeCst = b.create<arith::ConstantIndexOp>(minTaskSize); |
| |
| // Compute parallel block size from the parallel problem size: |
| // blockSize = min(tripCount, |
| // max(ceil_div(tripCount, maxComputeBlocks), |
| // ceil_div(minTaskSize, bodySize))) |
| Value bs0 = b.create<arith::CeilDivSIOp>(tripCount, maxComputeBlocks); |
| Value bs1 = b.create<arith::MaxSIOp>(bs0, minTaskSizeCst); |
| Value blockSize = b.create<arith::MinSIOp>(tripCount, bs1); |
| Value blockCount = b.create<arith::CeilDivSIOp>(tripCount, blockSize); |
| |
| // Create a parallel compute function that takes a block id and computes the |
| // parallel operation body for a subset of iteration space. |
| ParallelComputeFunction parallelComputeFunction = |
| createParallelComputeFunction(op, rewriter); |
| |
| // Dispatch parallel compute function using async recursive work splitting, |
| // or by submitting compute task sequentially from a caller thread. |
| if (asyncDispatch) { |
| doAsyncDispatch(b, rewriter, parallelComputeFunction, op, blockSize, |
| blockCount, tripCounts); |
| } else { |
| doSequentialDispatch(b, rewriter, parallelComputeFunction, op, blockSize, |
| blockCount, tripCounts); |
| } |
| |
| nb.create<scf::YieldOp>(); |
| }; |
| |
| // Replace the `scf.parallel` operation with the parallel compute function. |
| b.create<scf::IfOp>(TypeRange(), isZeroIterations, noOp, dispatch); |
| |
| // Parallel operation was replaced with a block iteration loop. |
| rewriter.eraseOp(op); |
| |
| return success(); |
| } |
| |
| void AsyncParallelForPass::runOnOperation() { |
| MLIRContext *ctx = &getContext(); |
| |
| RewritePatternSet patterns(ctx); |
| patterns.add<AsyncParallelForRewrite>(ctx, asyncDispatch, numWorkerThreads, |
| minTaskSize); |
| |
| if (failed(applyPatternsAndFoldGreedily(getOperation(), std::move(patterns)))) |
| signalPassFailure(); |
| } |
| |
| std::unique_ptr<Pass> mlir::createAsyncParallelForPass() { |
| return std::make_unique<AsyncParallelForPass>(); |
| } |
| |
| std::unique_ptr<Pass> mlir::createAsyncParallelForPass(bool asyncDispatch, |
| int32_t numWorkerThreads, |
| int32_t minTaskSize) { |
| return std::make_unique<AsyncParallelForPass>(asyncDispatch, numWorkerThreads, |
| minTaskSize); |
| } |
