bitsandbytes-rocm/bitsandbytes/autograd/_functions.py
2023-06-09 21:39:37 +02:00

568 lines
21 KiB
Python

import operator
import warnings
from dataclasses import dataclass
from functools import reduce # Required in Python 3
from typing import Tuple, Optional, List
import torch
import bitsandbytes.functional as F
# math.prod not compatible with python < 3.8
def prod(iterable):
return reduce(operator.mul, iterable, 1)
tensor = torch.Tensor
# The inverse transformation for the colTuring and colAmpere format were contributed by Alex Borzunov:
# https://github.com/bigscience-workshop/petals/blob/main/src/petals/utils/linear8bitlt_patch.py
"""
This class pools outlier dimensions across layers.
This is particularly important for small models where outlier features
are less systematic and occur with low frequency.
"""
class GlobalOutlierPooler:
_instance = None
def __init__(self):
raise RuntimeError("Call get_instance() instead")
def initialize(self):
self.outliers = set()
self.model_dim = None
@classmethod
def get_instance(cls):
if cls._instance is None:
cls._instance = cls.__new__(cls)
cls._instance.initialize()
return cls._instance
def add_outliers(self, outlier_idx, feature_dim):
if self.model_dim is None:
self.model_dim = feature_dim
if feature_dim != self.model_dim:
return # we do not encode outliers for the 2nd FFN layer
self.outliers.update(outlier_idx.tolist())
def get_current_outlier_idx(self):
return torch.Tensor(list(self.outliers)).to(torch.int64)
def get_inverse_transform_indices(transform_tile: callable, tile_size: Tuple[int, int]):
"""
Compute a permutation of indices that invert the specified (tiled) matrix transformation
:param transform_tile: a function that applies forward transform to a tensor of shape [dim1, dim2]
:param tile_size: higher-level tile dimensions, i.e. (8, 32) for Turing and (32, 32) for Ampere
:note: we assume that tile_transform applies to a cpu-based int8 tensor of shape tile_size
:example: transform_tile function for the turing layout (bitsandbytes.functional as F)
:returns: indices
"""
d1, d2 = tile_size
assert 0 < d1 * d2 < 2**64
tile_indices = torch.arange(d1 * d2, dtype=torch.int64).view(d1, d2)
# encode each position in tile as a tuple of <= 8 unique bytes
permuted_tile_indices = torch.zeros_like(tile_indices)
for i in range(8):
# select i-th byte, apply transformation and trace where each index ended up
ith_dim_indices = torch.div(tile_indices, 256**i, rounding_mode="trunc") % 256
sample_tile_i = (ith_dim_indices - 128).to(torch.int8).contiguous()
assert torch.all(sample_tile_i.int() + 128 == ith_dim_indices), "int overflow"
permuted_tile_i = transform_tile(sample_tile_i)
ith_permuted_indices = permuted_tile_i.to(tile_indices.dtype) + 128
permuted_tile_indices += ith_permuted_indices * (256**i)
if d1 * d2 < 256**i:
break # if all indices fit in i bytes, stop early
return permuted_tile_indices
def undo_layout(permuted_tensor: torch.Tensor, tile_indices: torch.LongTensor) -> torch.Tensor:
"""
Undo a tiled permutation such as turing or ampere layout
:param permuted_tensor: torch tensor in a permuted layout
:param tile_indices: reverse transformation indices, from get_inverse_transform_indices
:return: contiguous row-major tensor
"""
(rows, cols), (tile_rows, tile_cols) = permuted_tensor.shape, tile_indices.shape
assert rows % tile_rows == cols % tile_cols == 0, "tensor must contain a whole number of tiles"
tensor = permuted_tensor.reshape(-1, tile_indices.numel()).t()
outputs = torch.empty_like(tensor) # note: not using .index_copy because it was slower on cuda
outputs[tile_indices.flatten()] = tensor
outputs = outputs.reshape(tile_rows, tile_cols, cols // tile_cols, rows // tile_rows)
outputs = outputs.permute(3, 0, 2, 1) # (rows // tile_rows, tile_rows), (cols // tile_cols, tile_cols)
return outputs.reshape(rows, cols).contiguous()
class MatMul8bit(torch.autograd.Function):
@staticmethod
def forward(ctx, A, B, out=None, quant_type="vector", precision=None):
if precision is None:
precision = [8, 8, 8]
if precision[0] != 8:
with torch.no_grad():
output = torch.matmul(A, B)
else:
if len(B.shape) == 2:
dim = 0
else:
dim = 1
qA, SA = F.vectorwise_quant(A, dim=-1, quant_type=quant_type)
qB, SB = F.vectorwise_quant(B, dim=dim, quant_type=quant_type)
iout = F.igemm(qA, qB)
output = F.vectorwise_mm_dequant(iout, SA, SB, A.dtype, quant_type)
if A.requires_grad or B.requires_grad:
ctx.save_for_backward(A, B)
ctx.quant_type = quant_type
ctx.precision = precision
return output
@staticmethod
def backward(ctx, grad_output):
A, B = ctx.saved_tensors
quant_type = ctx.quant_type
precision = ctx.precision
grad_A = grad_B = None
if B.requires_grad:
if len(A.shape) == 3:
dims = [0, 1]
# bsi -> ibs
permute_dim = [0, 2, 1]
else:
dims = [0]
# bs -> sb
permute_dim = [1, 0]
if precision[1] != 8:
with torch.no_grad():
grad_B = torch.matmul(A.permute(permute_dim), grad_output)
else:
if len(B.shape) == 2 and len(A.shape) == 3:
grad_output = grad_output.contiguous()
if not grad_output.is_contiguous():
grad_output.contiguous()
qgrad_output, S1 = F.vectorwise_quant(
grad_output.view(-1, grad_output.shape[2]),
dim=0,
quant_type=quant_type,
)
if not A.is_contiguous():
A = A.contiguous()
qA, S2 = F.vectorwise_quant(
A.view(-1, A.shape[2]), dim=0, quant_type=quant_type
)
igrad_B = F.igemm(qA.t(), qgrad_output)
grad_B = F.vectorwise_mm_dequant(
igrad_B, S2.t(), S1, grad_output.dtype, quant_type
)
else:
qgrad_output, S1 = F.vectorwise_quant(
grad_output, dim=dims, quant_type=quant_type
)
qA, S2 = F.vectorwise_quant(
A, dim=dims, quant_type=quant_type
)
igrad_B = F.igemm(qA.permute(permute_dim), qgrad_output)
grad_B = F.vectorwise_mm_dequant(
igrad_B,
S2.permute(permute_dim),
S1,
grad_output.dtype,
quant_type,
)
if A.requires_grad:
if len(grad_output.shape) == 3:
dims = [2]
else:
dims = [1]
if len(B.shape) == 3:
# bio -> boi
permute_dim = [0, 2, 1]
dim_B = dims
else:
# io -> oi
permute_dim = [1, 0]
dim_B = [1]
if precision[2] != 8:
with torch.no_grad():
grad_A = torch.matmul(grad_output, B.permute(permute_dim))
else:
qgrad_output, S1 = F.vectorwise_quant(
grad_output, dim=dims, quant_type=quant_type
)
qB, S3 = F.vectorwise_quant(B, dim=dim_B, quant_type=quant_type)
igrad_A = F.igemm(qgrad_output, qB.permute(permute_dim))
grad_A = F.vectorwise_mm_dequant(
igrad_A,
S1,
S3.permute(permute_dim),
grad_output.dtype,
quant_type,
)
return grad_A, grad_B, None, None, None
mm_cublas = MatMul8bit.apply
bmm_cublas = MatMul8bit.apply
matmul_cublas = MatMul8bit.apply
def supports_igemmlt(device: torch.device) -> bool:
"""check if this device supports the optimized int8 kernel"""
if torch.cuda.get_device_capability(device=device) < (7, 5):
return False
device_name = torch.cuda.get_device_name(device=device)
nvidia16_models = ('GTX 1630', 'GTX 1650', 'GTX 1660') # https://en.wikipedia.org/wiki/GeForce_16_series
if any(model_name in device_name for model_name in nvidia16_models):
return False # these devices are technically cuda 7.5-capable, but they lack tensor cores
return True
def _get_tile_size(format):
assert format in (
"col_turing",
"col_ampere",
), f"please find this assert and manually enter tile size for {format}"
return (8, 32) if format == "col_turing" else (32, 32)
def get_tile_inds(format, device):
transform = lambda x: F.transform(x.to(device), from_order="row", to_order=format)[0].to(x.device)
with torch.no_grad():
return get_inverse_transform_indices(transform, _get_tile_size(format)).to(device)
@dataclass
class MatmulLtState:
_tile_indices: Optional[torch.Tensor] = None
force_no_igemmlt: bool = False
CB = None
CxB = None
SB = None
SCB = None
CxBt = None
SBt = None
CBt = None
subB = None
outlier_pool = None
has_accumulated_gradients = False
threshold = 0.0
idx = None
is_training = True
has_fp16_weights = True
memory_efficient_backward = False
use_pool = False
formatB = F.get_special_format_str()
def reset_grads(self):
self.CB = None
self.CxB = None
self.SB = None
self.SCB = None
self.CxBt = None
self.SBt = None
self.CBt = None
@property
def tile_indices(self):
if self._tile_indices is None:
self._tile_indices = get_tile_inds(self.formatB, self.CxB.device)
return self._tile_indices
class MatMul8bitLt(torch.autograd.Function):
# forward is the same, but we added the fallback for pre-turing GPUs
# backward is mostly the same, but adds one extra clause (see "elif state.CxB is not None")
@staticmethod
def forward(ctx, A, B, out=None, bias=None, state=MatmulLtState):
using_igemmlt = supports_igemmlt(A.device) and not state.force_no_igemmlt
# default of pytorch behavior if inputs are empty
ctx.is_empty = False
if prod(A.shape) == 0:
ctx.is_empty = True
ctx.A = A
ctx.B = B
ctx.bias = bias
if A.shape[-1] == B.shape[0]:
return torch.empty(A.shape[:-1] + B.shape[1:], dtype=A.dtype, device=A.device)
else:
return torch.empty(A.shape[:-1] + B.shape[:1], dtype=A.dtype, device=A.device)
# 1. Quantize A
# 2. Quantize B
# 3. Matmul
# 4. Mixed-precision decomposition matmul
# 5. Save state
formatB = state.formatB
input_shape = A.shape
if state.outlier_pool is None:
state.outlier_pool = GlobalOutlierPooler.get_instance()
# Cast A to fp16
if A.dtype != torch.float16:
warnings.warn(f"MatMul8bitLt: inputs will be cast from {A.dtype} to float16 during quantization")
# 1. Quantize A
if len(A.shape) == 3:
A = A.view(-1, A.shape[-1]).contiguous()
CA, CAt, SCA, SCAt, coo_tensorA = F.double_quant(A.to(torch.float16), threshold=state.threshold)
if state.threshold > 0.0 and coo_tensorA is not None:
if state.has_fp16_weights:
idx = torch.unique(coo_tensorA.colidx).long()
CA[:, idx] = 0
CAt[:, idx] = 0
subA = A[:, idx]
state.subB = B[:, idx].t().contiguous()
state.idx = idx
else:
if state.CxB is None and using_igemmlt:
# B in in 8-bit row-major, we can transform it back to 16-bit to extract outlier dimensions
# we also need to convert it to the turing/ampere format
state.CxB, state.SB = F.transform(state.CB, to_order=formatB)
else:
if not state.has_fp16_weights and state.CxB is None and using_igemmlt:
state.CxB, state.SB = F.transform(state.CB, to_order=formatB)
subA = None
# 2. Quantize B
if state.has_fp16_weights:
has_grad = True if (getattr(B, "grad", None) is not None) else False
is_transposed = not B.is_contiguous() and B.shape[0] == B.stride(1)
if is_transposed:
B = B.contiguous()
if (state.is_training and not has_grad) or state.CxB is None:
state.reset_grads()
(
CB,
state.CBt,
state.SCB,
state.SCBt,
coo_tensorB,
) = F.double_quant(B.to(torch.float16))
if using_igemmlt:
state.CxB, state.SB = F.transform(CB, to_order=formatB)
else:
state.CB = CB
else:
has_grad = False
if coo_tensorA is not None and not state.has_fp16_weights:
# extract outliers
outlier_idx = torch.unique(coo_tensorA.colidx)
state.idx = outlier_idx
# state.outlier_pool.add_outliers(outlier_idx, A.shape[-1])
# if state.use_pool and state.outlier_pool.model_dim == A.shape[-1]:
# # do not use pool for 2nd FFN layer
# state.idx = state.outlier_pool.get_current_outlier_idx().to(A.device)
# else:
# state.idx = outlier_idx
if state.CxB is not None:
outliers = F.extract_outliers(state.CxB, state.SB, state.idx.int())
else:
outliers = state.CB[:, state.idx.long()].clone()
state.subB = (outliers * state.SCB.view(-1, 1) / 127.0).t().contiguous().to(A.dtype)
CA[:, state.idx.long()] = 0
CAt[:, state.idx.long()] = 0
subA = A[:, state.idx.long()]
shapeB = state.SB[0] if state.SB else B.shape
if len(input_shape) == 3:
output_shape = (input_shape[0], input_shape[1], shapeB[0])
else:
output_shape = (input_shape[0], shapeB[0])
# 3. Matmul
if using_igemmlt:
C32A, SA = F.transform(CA, "col32")
out32, Sout32 = F.igemmlt(C32A, state.CxB, SA, state.SB)
if bias is None or bias.dtype == torch.float16:
# we apply the fused bias here
output = F.mm_dequant(out32, Sout32, SCA, state.SCB, bias=bias)
output = output.to(A.dtype)
else: # apply bias separately
output = F.mm_dequant(out32, Sout32, SCA, state.SCB, bias=None)
output = output.to(A.dtype).add_(bias)
else:
A_wo_outliers = A.clone()
if state.idx is not None:
A_wo_outliers[:, state.idx.long()] = 0
output = torch.nn.functional.linear(A_wo_outliers, state.CB.to(A.dtype))
output = output.mul_(state.SCB.unsqueeze(0).mul(1.0 / 127.0))
if bias is not None:
output = output.add_(bias)
# 4. Mixed-precision decomposition matmul
if coo_tensorA is not None and subA is not None:
output += torch.matmul(subA, state.subB)
# 5. Save state
ctx.state = state
ctx.formatB = formatB
ctx.grad_shape = input_shape
ctx.dtype_A, ctx.dtype_B, ctx.dtype_bias = A.dtype, B.dtype, None if bias is None else bias.dtype
if any(ctx.needs_input_grad[:2]):
ctx.tensors = (CAt, subA, A)
ctx.tensor_states = (SCAt, state.idx)
else:
ctx.tensors = [None, None, A]
ctx.tensor_states = (None, None)
ctx.save_for_backward(None, None)
clone_func = torch.clone if len(output_shape) == 3 else lambda x: x
return clone_func(output.view(output_shape))
@staticmethod
def backward(ctx, grad_output):
if ctx.is_empty:
bias_grad = None if ctx.bias is None else torch.zeros_like(ctx.bias)
return torch.zeros_like(ctx.A), torch.zeros_like(ctx.B), None, bias_grad, None
req_gradA, req_gradB, _, req_gradBias, _ = ctx.needs_input_grad
CAt, subA, A = ctx.tensors
SCAt, idx = ctx.tensor_states
formatB = ctx.formatB
state = ctx.state
grad_A = grad_B = grad_bias = None
if req_gradBias:
# compute grad_bias first before changing grad_output dtype
grad_bias = grad_output.sum(0, dtype=ctx.dtype_bias)
# Cast grad_output to fp16
if len(grad_output.shape) == 3:
grad_output = grad_output.reshape(-1, grad_output.shape[-1]).contiguous()
Cgrad, Cgradt, SCgrad, SCgradt, coo_tensor = F.double_quant(grad_output.to(torch.float16))
if req_gradB:
CxAt, SAt = F.transform(CAt, formatB, transpose=True)
C32grad, Sgrad = F.transform(Cgradt, "col32", transpose=True)
gradB32, SgradB32 = F.igemmlt(C32grad, CxAt, Sgrad, SAt)
grad_B = F.mm_dequant(gradB32, SgradB32, SCgradt, SCAt)
if state.threshold > 0.0 and subA is not None:
grad_B[:, idx] += torch.matmul(grad_output.t(), subA)
if req_gradA:
if state.CBt is not None:
C32grad, Sgrad = F.transform(Cgrad, "col32")
if state.CxBt is None:
state.CxBt, state.SBt = F.transform(state.CBt, to_order=formatB, transpose=True)
gradA32, SgradA32 = F.igemmlt(C32grad, state.CxBt, Sgrad, state.SBt)
grad_A = F.mm_dequant(gradA32, SgradA32, SCgrad, state.SCBt).view(ctx.grad_shape).to(ctx.dtype_A)
elif state.CB is not None:
CB = state.CB.to(ctx.dtype_A, copy=True).mul_(state.SCB.unsqueeze(1).mul(1.0 / 127.0))
grad_A = torch.matmul(grad_output, CB).view(ctx.grad_shape).to(ctx.dtype_A)
elif state.CxB is not None:
CB = (
undo_layout(state.CxB, state.tile_indices)
.to(ctx.dtype_A)
.mul_(state.SCB.unsqueeze(1).mul(1.0 / 127.0))
)
grad_A = torch.matmul(grad_output, CB).view(ctx.grad_shape).to(ctx.dtype_A)
else:
raise Exception("State must contain either CBt or CB or CxB matrix for backward")
return grad_A, grad_B, None, grad_bias, None
class MatMul4Bit(torch.autograd.Function):
# forward is the same, but we added the fallback for pre-turing GPUs
# backward is mostly the same, but adds one extra clause (see "elif state.CxB is not None")
@staticmethod
def forward(ctx, A, B, out=None, bias=None, state=None):
# default of pytorch behavior if inputs are empty
ctx.is_empty = False
if prod(A.shape) == 0:
ctx.is_empty = True
ctx.A = A
ctx.B = B
ctx.bias = bias
B_shape = state[1]
if A.shape[-1] == B_shape[0]:
return torch.empty(A.shape[:-1] + B_shape[1:], dtype=A.dtype, device=A.device)
else:
return torch.empty(A.shape[:-1] + B_shape[:1], dtype=A.dtype, device=A.device)
# 1. Dequantize
# 2. MatmulnN
output = torch.nn.functional.linear(A, F.dequantize_fp4(B, state).to(A.dtype).t(), bias)
# 3. Save state
ctx.state = state
ctx.dtype_A, ctx.dtype_B, ctx.dtype_bias = A.dtype, B.dtype, None if bias is None else bias.dtype
if any(ctx.needs_input_grad[:2]):
ctx.tensors = (A, B)
else:
ctx.tensors = (None, None)
return output
@staticmethod
def backward(ctx, grad_output):
if ctx.is_empty:
bias_grad = None if ctx.bias is None else torch.zeros_like(ctx.bias)
return torch.zeros_like(ctx.A), torch.zeros_like(ctx.B), None, bias_grad, None
req_gradA, _, _, req_gradBias, _= ctx.needs_input_grad
A, B = ctx.tensors
state = ctx.state
grad_A, grad_B, grad_bias = None, None, None
if req_gradBias:
# compute grad_bias first before changing grad_output dtype
grad_bias = grad_output.sum(0, dtype=ctx.dtype_bias)
# not supported by PyTorch. TODO: create work-around
#if req_gradB: grad_B = torch.matmul(grad_output.t(), A)
if req_gradA: grad_A = torch.matmul(grad_output, F.dequantize_fp4(B, ctx.state).to(grad_output.dtype).t())
return grad_A, grad_B, None, grad_bias, None
def matmul(
A: tensor,
B: tensor,
out: tensor = None,
state: MatmulLtState = None,
threshold=0.0,
bias=None
):
state = state or MatmulLtState()
if threshold > 0.0:
state.threshold = threshold
return MatMul8bitLt.apply(A, B, out, bias, state)
def matmul_4bit(A: tensor, B: tensor, quant_state: List, out: tensor = None, bias=None):
assert quant_state is not None
return MatMul4Bit.apply(A, B, out, bias, quant_state)