ethosu/vela/weight_compressor.py

# Copyright (C) 2020 Arm Limited or its affiliates. All rights reserved.
#
# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the License); you may
# not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an AS IS BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


# Description:
# Compresses and pads the weigths. It also calculates the scales and packs with the biases.

import os
import sys
import enum
import math
import numpy as np
from collections import namedtuple
from .numeric_util import round_up
from .scaling import quantise_scale
from .tensor import TensorPurpose, TensorSubPurpose, TensorFormat, TensorBlockTraversal
from .operation import NpuBlockType
from .architecture_features import Block
from .nn_graph import SchedulingStrategy
from .data_type import DataType

from ethosu import mlw_codec


def encode(weight_stream):
    assert np.amin(weight_stream) >= -255
    assert np.amax(weight_stream) <= 255

    # Encode flattened signed weight stream
    compressed = mlw_codec.encode(weight_stream)

    # pad with 0xFF as needed so the length of the weight stream
    # is a multiple of 16
  
    while (len(compressed) % 16) != 0:
        compressed.append(0xFF)

    return compressed


def generate_brick(arch, brick_weights, ofm_block, block_traversal, ifm_bitdepth):
    is_depthwise = block_traversal == TensorBlockTraversal.DepthWise
    is_partkernel = block_traversal == TensorBlockTraversal.PartKernelFirst
    subkernel_max = arch.subkernel_max
    ofm_ublock = arch.ofm_ublock
    ifm_ublock = arch.ifm_ublock
    # Expect weights formatted HWIO
    ofm_depth = brick_weights.shape[-1]
    ifm_depth = brick_weights.shape[-2]
    kernel_width = brick_weights.shape[-3]
    kernel_height = brick_weights.shape[-4]
    # IFM block depth
    if is_partkernel or (ifm_bitdepth == 16):
        # IFM block depth is always 16 for part-kernel-first
        ifm_block_depth = 16
    elif ifm_bitdepth == 8:
        ifm_block_depth = 32
    else:
        assert False

    stream = []

    # Top level striping - OFM blocks in the entire brick's depth
    for ofm_block_z in range(0, ofm_depth, ofm_block.depth):
        clipped_ofm_block_depth = min(ofm_block.depth, ofm_depth - ofm_block_z)
        # IFM blocks required for the brick
        for ifm_block_z in range(0, (1 if is_depthwise else ifm_depth), ifm_block_depth):
            if is_depthwise:
                clipped_ifm_block_depth = ifm_ublock.depth
            else:
                clipped_ifm_block_depth = (
                    min(ifm_block_depth, ifm_depth - ifm_block_z) if is_partkernel else ifm_block_depth
                )
            # Weight decomposition
            # Subkernel Splitting  (H)
            for subkernel_y in range(0, kernel_height, subkernel_max.height):
                sub_height = min(kernel_height - subkernel_y, subkernel_max.height)
                # Subkernel splitting (W)
                for subkernel_x in range(0, kernel_width, subkernel_max.width):
                    sub_width = min(kernel_width - subkernel_x, subkernel_max.width)
                    subkernel_elements = sub_width * sub_height
                    # Part kernel first works across the kernel H/W and needs padding
                    if is_partkernel:
                        if ifm_bitdepth == 16 and subkernel_elements % 2 != 0:
                            subkernel_elements = int(math.ceil(subkernel_elements / 2) * 2)
                        elif ifm_bitdepth == 8 and subkernel_elements % 4 != 0:
                            subkernel_elements = int(math.ceil(subkernel_elements / 4) * 4)

                    # Depthwise Conv requires multiple of 4 kernel elements in its weight block
                    # this is different from normal conv which is considered "weights depth-first"
                    elif is_depthwise:
                        subkernel_elements = int(math.ceil(subkernel_elements / 4.0) * 4)

                    ifm_block_depth_outer = clipped_ifm_block_depth if is_partkernel else 1
                    ifm_block_depth_inner = 1 if is_partkernel else clipped_ifm_block_depth
                    # IFM Ublocks in IFM-block over depth for part-kernel-first mode
                    # For depth-first IFM Ublocks are traversed after subkernel elements so this loop is ignored.
                    for ifm_ublk_outer in range(0, ifm_block_depth_outer, ifm_ublock.depth):
                        # OFM Ublocks in OFM-block over depth
                        for ofm_ublk in range(0, clipped_ofm_block_depth, ofm_ublock.depth):
                            # HW Kernel element traversal - cannot be a H/W loop due to element
                            # padding requirement on depthwise/part-kernel configurations
                            for element in range(subkernel_elements):
                                kx = element % sub_width
                                ky = element // sub_width
                                # IFM Ublocks in IFM-block over depth (only 1 ublock if depthwise)
                                # In case of part-kernel-first IFM Ublock traversal have already been handled
                                # and this loop is ignored.
                                for ifm_ublk_inner in range(0, ifm_block_depth_inner, ifm_ublock.depth):
                                    # Feed OFM ublock elements
                                    for ofm_ublock_z in range(ofm_ublock.depth):
                                        # Source IFM ublock elements (only 1 element deep if depthwise)
                                        for ifm_ublock_z in range(1 if is_depthwise else ifm_ublock.depth):
                                            # Source position within the current subkernel
                                            wx = subkernel_x + kx
                                            wy = subkernel_y + ky
                                            # Source IFM/OFM slices
                                            ifm_ublk = ifm_ublk_inner + ifm_ublk_outer
                                            ifm_z = ifm_block_z + ifm_ublk + ifm_ublock_z
                                            ofm_z = ofm_block_z + ofm_ublk + ofm_ublock_z
                                            if (ifm_z >= ifm_depth) or (ofm_z >= ofm_depth) or (ky >= sub_height):
                                                stream.append(0)
                                            else:
                                                stream.append(brick_weights[wy][wx][ifm_z][ofm_z])
    return stream


# Compress the weights
def compress_weights(tens, arch, npu_block_type, ofm_block, ofm_depth_step, min_val=None, max_val=None):
    assert tens.purpose == TensorPurpose.Weights
    assert tens.format == TensorFormat.WeightsCompressed

    WeightCompressionConfig = namedtuple("WeightCompressionConfig", ["npu_block_type", "ofm_block", "ofm_depth_step"])

    # check if weights have already been compressed
    wcc = tens.weight_compression_config
    if wcc is not None:
        assert wcc.npu_block_type == npu_block_type, "Weights not used by the same operator type"

        if wcc.ofm_block == ofm_block and wcc.ofm_depth_step == ofm_depth_step:
            return

    assert tens.quantization is not None
    assert tens.quantization.scale_f32 is not None
    assert tens.quantization.zero_point is not None

    zero_point = tens.quantization.zero_point
    quant_buf = tens.quant_values.astype(np.int64)

    # Early zero-point correction
    weights = quant_buf - zero_point

    if len(weights.shape) == 2:
        weights = np.expand_dims(np.expand_dims(weights, axis=0), axis=0)
        weights_shape = (weights.shape[0], 1, 1, weights.shape[1])
    else:
        weights_shape = weights.shape

    compression_scales = []
    compressed_offsets = []
    encoded_streams = []
    offset = 0
    max_single_buffer_len = 0

    ifm_bitdepth = tens.consumer_list[0].inputs[0].dtype.size_in_bits()
    ifm_depth = weights.shape[-2]
    if npu_block_type == NpuBlockType.ConvolutionDepthWise:
        tens.block_traversal = TensorBlockTraversal.DepthWise
    if npu_block_type == NpuBlockType.ConvolutionMxN:
        # Determine which block traversal strategy has better DPU utilization
        kernel_size = weights_shape[0] * weights_shape[1]
        depth_utilization = weights_shape[2] / round_up(weights_shape[2], 32 if ifm_bitdepth == 8 else 16)
        part_kernel_utilization = (weights_shape[2] / round_up(weights_shape[2], 8)) * (
            kernel_size / round_up(kernel_size, 4 if ifm_bitdepth == 8 else 2)
        )
        if part_kernel_utilization >= depth_utilization or ifm_depth <= 8:
            # Part-kernel first is always better for ifm depths <= 8
            tens.block_traversal = TensorBlockTraversal.PartKernelFirst
        else:
            tens.block_traversal = TensorBlockTraversal.DepthFirst

    # Slice weight stream up depth-ways into bricks and compress
    full_ofm_depth = quant_buf.shape[-1]
    for idx in range(0, full_ofm_depth, ofm_depth_step):
        # Get the weights necessary for this brick
        count = min(full_ofm_depth - idx, ofm_depth_step)
        brick_weights = weights[:, :, :, idx : idx + count]

        # Encode all weights into one chunk
        raw_stream = generate_brick(arch, brick_weights, ofm_block, tens.block_traversal, ifm_bitdepth)
        encoded = encode(raw_stream)
        encoded_streams.append(encoded)

        # Remember maximum encoded length for DoubleBuffering
        if max_single_buffer_len < len(encoded):
            max_single_buffer_len = len(encoded)

        # Remember where we put it for linear addressing
        compressed_offsets.append(offset)
        offset += len(encoded)
        assert offset % 16 == 0

        # Compression scale tracking
        compression_scales.append(len(encoded) / len(raw_stream))

    # Also track complete length in the offsets array
    compressed_offsets.append(offset)

    if tens.sub_purpose == TensorSubPurpose.DoubleBuffer and len(encoded_streams) > 2:
        offset = 2 * max_single_buffer_len
        assert offset % 16 == 0

    tens.storage_shape = [1, 1, 1, offset]
    tens.weight_compression_scales = compression_scales
    tens.weight_compression_config = WeightCompressionConfig(npu_block_type, ofm_block, ofm_depth_step)
    tens.weight_compressed_offsets = compressed_offsets
    tens.compression_scale_for_worst_weight_stream = np.amax(compression_scales)
    tens.storage_compression_scale = tens.bandwidth_compression_scale = np.average(compression_scales)
    tens.compressed_values = encoded_streams
    tens.brick_size = (weights_shape[0], weights_shape[1], weights_shape[2], min(tens.shape[-1], ofm_depth_step))


def calc_scales_and_pack_biases(tens, arch, oc_quantum, rescale_for_faf=False):
    assert tens.purpose == TensorPurpose.FeatureMap
    assert tens.format == TensorFormat.NHWC
    # the connected operator should expect a bias input unless it is a FullyConnected
    assert "Bias" in tens.consumer_list[0].type or tens.consumer_list[0].type.startswith("FullyConnected")
    # the input bias tensor is the same as that connected to the operator
    assert tens is tens.consumer_list[0].inputs[2]
    # the operator should only have a single output
    assert len(tens.consumer_list[0].outputs) == 1

    def pack_bias_and_scale(bias, scale, shift):
        bias = np.int64(bias)
        assert -(1 << (40 - 1)) <= bias < (1 << (40 - 1))  # signed 40-bit range
        assert 0 <= scale < (1 << 32)  # unsigned 32-bit range
        assert 0 <= shift < (1 << 6)  # unsigned 6-bit range

        # pack the 80 bit value = [0(2-bits),shift(6-bits),scale(32-bits),bias(40-bits)]
        data = bytearray(10)
        data[0] = (bias >> (0 * 8)) & 0xFF
        data[1] = (bias >> (1 * 8)) & 0xFF
        data[2] = (bias >> (2 * 8)) & 0xFF
        data[3] = (bias >> (3 * 8)) & 0xFF
        data[4] = (bias >> (4 * 8)) & 0xFF
        data[5] = (scale >> (0 * 8)) & 0xFF
        data[6] = (scale >> (1 * 8)) & 0xFF
        data[7] = (scale >> (2 * 8)) & 0xFF
        data[8] = (scale >> (3 * 8)) & 0xFF
        data[9] = shift & 0x3F
        return data

    biases = tens.quant_values

    first_consumer_op = tens.consumer_list[0]
    ifm_dtype = first_consumer_op.inputs[0].dtype
    ifm_scale = first_consumer_op.inputs[0].quantization.scale_f32
    ofm_scale = first_consumer_op.outputs[0].quantization.scale_f32
    weight_scales = first_consumer_op.inputs[1].quantization.scale_f32

    # biases can have multiple consumers for rnn cells. if so, then check that they are all the same
    for op in tens.consumer_list[1:]:
        assert ifm_scale == op.inputs[0].quantization.scale_f32
        assert ofm_scale == op.outputs[0].quantization.scale_f32
        assert weight_scales == op.inputs[1].quantization.scale_f32

    if not hasattr(weight_scales, "__iter__"):
        # If weight_scales is not already an iterable make it into a list
        weight_scales = [weight_scales]

    # Convert scales to np.double (from np.float32) to conform to TensorFlow Lite which
    # uses double during scaling calculations
    # TensorFlow Lite casts the scales slightly differently for uint8 and int8
    if not rescale_for_faf:
        if ifm_dtype == DataType.uint8:
            scales = [np.double(ifm_scale * weight_scale) / np.double(ofm_scale) for weight_scale in weight_scales]
        elif ifm_dtype == DataType.int8:
            scales = [
                (np.double(ifm_scale) * np.double(weight_scale)) / np.double(ofm_scale)
                for weight_scale in weight_scales
            ]
        else:
            assert False, str(ifm_dtype) + " not implemented"
    else:
        if ifm_dtype == DataType.uint8:
            scales = [np.double(ifm_scale * weight_scale * 0x3000) for weight_scale in weight_scales]
        elif ifm_dtype == DataType.int8:
            scales = [(np.double(ifm_scale * 0x3000) * np.double(weight_scale)) for weight_scale in weight_scales]
        else:
            assert False, str(ifm_dtype) + " not implemented"

    # quantise all of the weight scales into (scale_factor, shift)
    quantised_scales = [quantise_scale(scale) for scale in scales]

    for _, shift in quantised_scales:
        assert shift >= 16

    # pack the biases and scales
    tens.compressed_values = []
    if len(quantised_scales) == 1:
        # If only 1 quantised scale is used, repeat that value for the length of the biases
        quantised_scales = [quantised_scales[0]] * len(biases)

    assert len(quantised_scales) == len(biases)
    for i, bias in enumerate(biases):
        tens.compressed_values.append(pack_bias_and_scale(bias, *quantised_scales[i]))

    tens.element_size_bytes = 10

    # Figure out if we need padded storage (extra whole elements)
    padding = (len(tens.compressed_values) * tens.element_size_bytes) % 16
    if padding != 0:
        padding = 16 - padding

    # This adds enough padding to allow over-reads
    while padding > 0:
        tens.compressed_values.append(pack_bias_and_scale(0, 0, 0))
        padding = padding - tens.element_size_bytes

    tens.storage_shape = [len(tens.compressed_values)]


def update_pass_weight_and_scale_tensors(nng, arch):
    def find_npu_usage_of_tensor(tens):
        # TODO: This function is identical to the one in mark_tensors.py. A common version should be used.
        for op in tens.consumers():
            if op.type == "DMA":
                return find_npu_usage_of_tensor(op.outputs[0])
            if "npu_block_type" in op.attrs:
                return op.attrs["npu_block_type"]
            return NpuBlockType.Default

    for sg in nng.subgraphs:
        for ps in sg.passes:
            if ps.weight_tensor != None:
                npu_usage_of_tensor = find_npu_usage_of_tensor(ps.weight_tensor)
                if npu_usage_of_tensor == NpuBlockType.ConvolutionDepthWise:
                    ps.weight_tensor.quant_values = np.transpose(ps.weight_tensor.quant_values, (0, 1, 3, 2))
                    ps.weight_tensor.shape = ps.weight_tensor.storage_shape = ps.weight_tensor.bandwidth_shape = list(
                        ps.weight_tensor.quant_values.shape
                    )
                    ps.weight_tensor.weight_transpose_depthwise = True

                needs_dma = len(ps.weight_tensor.ops) == 1 and ps.weight_tensor.ops[0].type == "DMA"
                if ps.cascade.strategy == SchedulingStrategy.WeightStream and needs_dma:
                    ofm_depth_step = ps.block_config[-1]
                else:
                    ofm_depth_step = ps.weight_tensor.shape[-1]

                compress_weights(
                    ps.weight_tensor,
                    arch,
                    npu_usage_of_tensor,
                    Block(ps.block_config[-3], ps.block_config[-4], ps.block_config[-1]),
                    ofm_depth_step,
                )
                # Update source tensor
                if len(ps.weight_tensor.ops) == 1 and ps.weight_tensor.ops[0].type == "DMA":
                    src_tens = ps.weight_tensor.ops[0].inputs[0]
                    src_tens.shape = ps.weight_tensor.shape
                    src_tens.weight_transpose_depthwise = ps.weight_tensor.weight_transpose_depthwise
                    src_tens.quant_values = ps.weight_tensor.quant_values
                    src_tens.compressed_values = ps.weight_tensor.compressed_values
                    src_tens.storage_shape = [1, 1, 1, ps.weight_tensor.weight_compressed_offsets[-1]]
                    src_tens.brick_size = ps.weight_tensor.brick_size
                    src_tens.weight_compression_scales = ps.weight_tensor.weight_compression_scales
                    src_tens.weight_compressed_offsets = ps.weight_tensor.weight_compressed_offsets

            if ps.scale_tensor != None:
                rescale_for_faf = False
                activation_ops = set(("Sigmoid", "Tanh"))
                if (ps.ops[-1].type in activation_ops) and (ps.npu_block_type != NpuBlockType.ElementWise):
                    rescale_for_faf = True
                calc_scales_and_pack_biases(ps.scale_tensor, arch, ps.block_config[3], rescale_for_faf)