Spatial SVD

Context

Spatial singular value decomposition (spatial SVD) is a tensor decomposition technique which decomposes one large layer (in terms of Multiply-accumulate(MAC) or memory) into two smaller layers.

Consider a convolution (Conv) layer with kernel (𝑚, 𝑛, ℎ, 𝑤), where:

• 𝑚 is the input channels

• 𝑛 the output channels

• ℎ is the height of the kernel

• 𝑤 is the width of the kernel

Spatial SVD decomposes the kernel into two kernels, one of size (𝑚, 𝑘, ℎ, 1) and one of size (𝑘, 𝑛, 1, 𝑤), where 𝑘 is called the rank. The smaller the value of 𝑘, the larger the degree of compression.

The following figure illustrates how spatial SVD decomposes both the output channel dimension and the size of the Conv kernel itself.

Workflow

Code example

Setup

PyTorch

Compressing using Spatial SVD

PyTorch

Compressing using Spatial SVD in auto mode with multiplicity = 8 for rank rounding

Compressing using Spatial SVD in manual mode

API

PyTorch

Top-level API for Compression

class aimet_torch.compress.ModelCompressor

AIMET model compressor: Enables model compression using various schemes

static ModelCompressor.compress_model(model, eval_callback, eval_iterations, input_shape, compress_scheme, cost_metric, parameters, trainer=None, visualization_url=None)

Compress a given model using the specified parameters

Parameters:

• model (Module) – Model to compress

• eval_callback (Callable[[Any, Optional[int], bool], float]) – Evaluation callback. Expected signature is evaluate(model, iterations, use_cuda). Expected to return an accuracy metric.

• eval_iterations – Iterations to run evaluation for

• trainer – Training Class: Contains a callable, train_model, which takes model, layer which is being fine tuned and an optional parameter train_flag as a parameter None: If per layer fine tuning is not required while creating the final compressed model

• input_shape (Tuple) – Shape of the input tensor for model

• compress_scheme (CompressionScheme) – Compression scheme. See the enum for allowed values

• cost_metric (CostMetric) – Cost metric to use for the compression-ratio (either mac or memory)

• parameters (Union[SpatialSvdParameters, WeightSvdParameters, ChannelPruningParameters]) – Compression parameters specific to given compression scheme

• visualization_url – url the user will need to input where visualizations will appear

Return type:

Tuple[Module, CompressionStats]

Returns:

A tuple of the compressed model, and compression statistics

Greedy Selection Parameters

class aimet_torch.common.defs.GreedySelectionParameters(target_comp_ratio, num_comp_ratio_candidates=10, use_monotonic_fit=False, saved_eval_scores_dict=None)

Configuration parameters for the Greedy compression-ratio selection algorithm

Variables:

• target_comp_ratio – Target compression ratio. Expressed as value between 0 and 1. Compression ratio is the ratio of cost of compressed model to cost of the original model.

• num_comp_ratio_candidates – Number of comp-ratio candidates to analyze per-layer More candidates allows more granular distribution of compression at the cost of increased run-time during analysis. Default value=10. Value should be greater than 1.

• use_monotonic_fit – If True, eval scores in the eval dictionary are fitted to a monotonically increasing function. This is useful if you see the eval dict scores for some layers are not monotonically increasing. By default, this option is set to False.

• saved_eval_scores_dict – Path to the eval_scores dictionary pickle file that was saved in a previous run. This is useful to speed-up experiments when trying different target compression-ratios for example. aimet will save eval_scores dictionary pickle file automatically in a ./data directory relative to the current path. num_comp_ratio_candidates parameter will be ignored when this option is used.

Configuration Definitions

class aimet_torch.common.defs.CostMetric(value)

Enumeration of metrics to measure cost of a model/layer

mac = 1

Cost modeled for compute requirements

Type:

MAC

memory = 2

Cost modeled for space requirements

Type:

Memory

class aimet_torch.common.defs.CompressionScheme(value)

Enumeration of compression schemes supported in aimet

channel_pruning = 3

Channel Pruning

spatial_svd = 2

Spatial SVD

weight_svd = 1

Weight SVD

Spatial SVD Configuration

class aimet_torch.defs.SpatialSvdParameters(mode, params, multiplicity=1)

Configuration parameters for spatial svd compression

Parameters:

• mode (Mode) – Either auto mode or manual mode

• params (Union[ManualModeParams, AutoModeParams]) – Parameters for the mode selected

• multiplicity – The multiplicity to which ranks/input channels will get rounded. Default: 1

class AutoModeParams(greedy_select_params, modules_to_ignore=None)

Configuration parameters for auto-mode compression

Parameters:

• greedy_select_params (GreedySelectionParameters) – Params for greedy comp-ratio selection algorithm

• modules_to_ignore (Optional[List[Module]]) – List of modules to ignore (None indicates nothing to ignore)

class ManualModeParams(list_of_module_comp_ratio_pairs)

Configuration parameters for manual-mode spatial svd compression

Parameters:

list_of_module_comp_ratio_pairs (List[ModuleCompRatioPair]) – List of (module, comp-ratio) pairs

class Mode(value)

Mode enumeration

auto = 2

Auto mode

manual = 1

Manual mode