diff options
Diffstat (limited to 'unsupported/Eigen/CXX11/src/Tensor/TensorCostModel.h')
-rw-r--r-- | unsupported/Eigen/CXX11/src/Tensor/TensorCostModel.h | 212 |
1 files changed, 212 insertions, 0 deletions
diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorCostModel.h b/unsupported/Eigen/CXX11/src/Tensor/TensorCostModel.h new file mode 100644 index 000000000..83c449cf1 --- /dev/null +++ b/unsupported/Eigen/CXX11/src/Tensor/TensorCostModel.h @@ -0,0 +1,212 @@ +// This file is part of Eigen, a lightweight C++ template library +// for linear algebra. +// +// Copyright (C) 2016 Rasmus Munk Larsen <rmlarsen@google.com> +// +// This Source Code Form is subject to the terms of the Mozilla +// Public License v. 2.0. If a copy of the MPL was not distributed +// with this file, You can obtain one at http://mozilla.org/MPL/2.0/. + +#ifndef EIGEN_CXX11_TENSOR_TENSOR_COST_MODEL_H +#define EIGEN_CXX11_TENSOR_TENSOR_COST_MODEL_H + +namespace Eigen { + +/** \class TensorEvaluator + * \ingroup CXX11_Tensor_Module + * + * \brief A cost model used to limit the number of threads used for evaluating + * tensor expression. + * + */ + +// Class storing the cost of evaluating a tensor expression in terms of the +// estimated number of operand bytes loads, bytes stored, and compute cycles. +class TensorOpCost { + public: + // TODO(rmlarsen): Fix the scalar op costs in Eigen proper. Even a simple + // model based on minimal reciprocal throughput numbers from Intel or + // Agner Fog's tables would be better than what is there now. + template <typename ArgType> + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE int MulCost() { + return internal::functor_traits< + internal::scalar_product_op<ArgType, ArgType> >::Cost; + } + template <typename ArgType> + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE int AddCost() { + return internal::functor_traits<internal::scalar_sum_op<ArgType> >::Cost; + } + template <typename ArgType> + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE int DivCost() { + return internal::functor_traits< + internal::scalar_quotient_op<ArgType, ArgType> >::Cost; + } + template <typename ArgType> + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE int ModCost() { + return internal::functor_traits<internal::scalar_mod_op<ArgType> >::Cost; + } + template <typename SrcType, typename TargetType> + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE int CastCost() { + return internal::functor_traits< + internal::scalar_cast_op<SrcType, TargetType> >::Cost; + } + + EIGEN_DEVICE_FUNC + TensorOpCost() : bytes_loaded_(0), bytes_stored_(0), compute_cycles_(0) {} + EIGEN_DEVICE_FUNC + TensorOpCost(double bytes_loaded, double bytes_stored, double compute_cycles) + : bytes_loaded_(bytes_loaded), + bytes_stored_(bytes_stored), + compute_cycles_(compute_cycles) {} + + EIGEN_DEVICE_FUNC + TensorOpCost(double bytes_loaded, double bytes_stored, double compute_cycles, + bool vectorized, double packet_size) + : bytes_loaded_(bytes_loaded), + bytes_stored_(bytes_stored), + compute_cycles_(vectorized ? compute_cycles / packet_size + : compute_cycles) { + eigen_assert(bytes_loaded >= 0 && (numext::isfinite)(bytes_loaded)); + eigen_assert(bytes_stored >= 0 && (numext::isfinite)(bytes_stored)); + eigen_assert(compute_cycles >= 0 && (numext::isfinite)(compute_cycles)); + } + + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE double bytes_loaded() const { + return bytes_loaded_; + } + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE double bytes_stored() const { + return bytes_stored_; + } + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE double compute_cycles() const { + return compute_cycles_; + } + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE double total_cost( + double load_cost, double store_cost, double compute_cost) const { + return load_cost * bytes_loaded_ + store_cost * bytes_stored_ + + compute_cost * compute_cycles_; + } + + // Drop memory access component. Intended for cases when memory accesses are + // sequential or are completely masked by computations. + EIGEN_DEVICE_FUNC void dropMemoryCost() { + bytes_loaded_ = 0; + bytes_stored_ = 0; + } + + // TODO(rmlarsen): Define min in terms of total cost, not elementwise. + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE TensorOpCost cwiseMin( + const TensorOpCost& rhs) const { + double bytes_loaded = numext::mini(bytes_loaded_, rhs.bytes_loaded()); + double bytes_stored = numext::mini(bytes_stored_, rhs.bytes_stored()); + double compute_cycles = numext::mini(compute_cycles_, rhs.compute_cycles()); + return TensorOpCost(bytes_loaded, bytes_stored, compute_cycles); + } + + // TODO(rmlarsen): Define max in terms of total cost, not elementwise. + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE TensorOpCost cwiseMax( + const TensorOpCost& rhs) const { + double bytes_loaded = numext::maxi(bytes_loaded_, rhs.bytes_loaded()); + double bytes_stored = numext::maxi(bytes_stored_, rhs.bytes_stored()); + double compute_cycles = numext::maxi(compute_cycles_, rhs.compute_cycles()); + return TensorOpCost(bytes_loaded, bytes_stored, compute_cycles); + } + + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE TensorOpCost& operator+=( + const TensorOpCost& rhs) { + bytes_loaded_ += rhs.bytes_loaded(); + bytes_stored_ += rhs.bytes_stored(); + compute_cycles_ += rhs.compute_cycles(); + return *this; + } + + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE TensorOpCost& operator*=(double rhs) { + bytes_loaded_ *= rhs; + bytes_stored_ *= rhs; + compute_cycles_ *= rhs; + return *this; + } + + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE friend TensorOpCost operator+( + TensorOpCost lhs, const TensorOpCost& rhs) { + lhs += rhs; + return lhs; + } + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE friend TensorOpCost operator*( + TensorOpCost lhs, double rhs) { + lhs *= rhs; + return lhs; + } + EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE friend TensorOpCost operator*( + double lhs, TensorOpCost rhs) { + rhs *= lhs; + return rhs; + } + + friend std::ostream& operator<<(std::ostream& os, const TensorOpCost& tc) { + return os << "[bytes_loaded = " << tc.bytes_loaded() + << ", bytes_stored = " << tc.bytes_stored() + << ", compute_cycles = " << tc.compute_cycles() << "]"; + } + + private: + double bytes_loaded_; + double bytes_stored_; + double compute_cycles_; +}; + +// TODO(rmlarsen): Implement a policy that chooses an "optimal" number of theads +// in [1:max_threads] instead of just switching multi-threading off for small +// work units. +template <typename Device> +class TensorCostModel { + public: + // Scaling from Eigen compute cost to device cycles. + static const int kDeviceCyclesPerComputeCycle = 1; + + // Costs in device cycles. + static const int kStartupCycles = 100000; + static const int kPerThreadCycles = 100000; + static const int kTaskSize = 40000; + + // Returns the number of threads in [1:max_threads] to use for + // evaluating an expression with the given output size and cost per + // coefficient. + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE int numThreads( + double output_size, const TensorOpCost& cost_per_coeff, int max_threads) { + double cost = totalCost(output_size, cost_per_coeff); + int threads = (cost - kStartupCycles) / kPerThreadCycles + 0.9; + return numext::mini(max_threads, numext::maxi(1, threads)); + } + + // taskSize assesses parallel task size. + // Value of 1.0 means ideal parallel task size. Values < 1.0 mean that task + // granularity needs to be increased to mitigate parallelization overheads. + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE double taskSize( + double output_size, const TensorOpCost& cost_per_coeff) { + return totalCost(output_size, cost_per_coeff) / kTaskSize; + } + + private: + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE double totalCost( + double output_size, const TensorOpCost& cost_per_coeff) { + // Cost of memory fetches from L2 cache. 64 is typical cache line size. + // 11 is L2 cache latency on Haswell. + // We don't know whether data is in L1, L2 or L3. But we are most interested + // in single-threaded computational time around 100us-10ms (smaller time + // is too small for parallelization, larger time is not intersting + // either because we are probably using all available threads already). + // And for the target time range, L2 seems to be what matters. Data set + // fitting into L1 is too small to take noticeable time. Data set fitting + // only into L3 presumably will take more than 10ms to load and process. + const double kLoadCycles = 1.0 / 64 * 11; + const double kStoreCycles = 1.0 / 64 * 11; + // Scaling from Eigen compute cost to device cycles. + return output_size * + cost_per_coeff.total_cost(kLoadCycles, kStoreCycles, + kDeviceCyclesPerComputeCycle); + } +}; + +} // namespace Eigen + +#endif // EIGEN_CXX11_TENSOR_TENSOR_COST_MODEL_H |