Merge branch 'main' into patch-1

CHANGELOG.md

@@ -189,3 +189,15 @@ Improvements:
  - StableEmbedding layer now has device and dtype parameters to make it 1:1 replaceable with regular Embedding layers (@lostmsu)
  - runtime performance of block-wise quantization slightly improved
  - added error message for the case multiple libcudart.so are installed and bitsandbytes picks the wrong one
+
+
+### 0.37.0
+
+#### Int8 Matmul + backward support for all GPUs
+
+Features:
+ - Int8 MatmulLt now supports backward through inversion of the ColTuring/ColAmpere format. Slow, but memory efficient. Big thanks to @borzunov
+ - Int8 now supported on all GPUs. On devices with compute capability < 7.5, the Int weights are cast to 16/32-bit for the matrix multiplication. Contributed by @borzunov
+
+Improvements:
+ - Improved logging for the CUDA detection mechanism.

Makefile

@@ -60,8 +60,8 @@ CC_ADA_HOPPER += -gencode arch=compute_90,code=sm_90
 
 
 all: $(ROOT_DIR)/dependencies/cub $(BUILD_DIR) env
-	$(NVCC) $(COMPUTE_CAPABILITY) $(CC_KEPLER) -Xcompiler '-fPIC' --use_fast_math -Xptxas=-v -dc $(FILES_CUDA) $(INCLUDE) $(LIB) --output-directory $(BUILD_DIR)
-	$(NVCC) $(COMPUTE_CAPABILITY) $(CC_KEPLER) -Xcompiler '-fPIC' -dlink $(BUILD_DIR)/ops.o $(BUILD_DIR)/kernels.o -o $(BUILD_DIR)/link.o
+	$(NVCC) $(CC_CUDA10x) -Xcompiler '-fPIC' --use_fast_math -Xptxas=-v -dc $(FILES_CUDA) $(INCLUDE) $(LIB) --output-directory $(BUILD_DIR)
+	$(NVCC) $(CC_CUDA10x) -Xcompiler '-fPIC' -dlink $(BUILD_DIR)/ops.o $(BUILD_DIR)/kernels.o -o $(BUILD_DIR)/link.o
 	$(GPP) -std=c++14 -DBUILD_CUDA -shared -fPIC $(INCLUDE) $(BUILD_DIR)/ops.o $(BUILD_DIR)/kernels.o $(BUILD_DIR)/link.o $(FILES_CPP) -o ./bitsandbytes/libbitsandbytes_cuda$(CUDA_VERSION).so $(LIB)
 
 cuda92: $(ROOT_DIR)/dependencies/cub $(BUILD_DIR) env

README.md

@@ -12,6 +12,7 @@ Resources:
 ## TL;DR
 **Requirements**
 Python >=3.8. Linux distribution (Ubuntu, MacOS, etc.) + CUDA > 10.0. LLM.int8() requires Turing or Ampere GPUs.
+
 **Installation**:
 ``pip install bitsandbytes``
 
@@ -58,6 +59,10 @@ The bitsandbytes library is currently only supported on Linux distributions. Win
 
 The requirements can best be fulfilled by installing pytorch via anaconda. You can install PyTorch by following the ["Get Started"](https://pytorch.org/get-started/locally/) instructions on the official website.
 
+To install run:
+
+``pip install bitsandbytes``
+
 ## Using bitsandbytes
 
 ### Using Int8 Matrix Multiplication

bitsandbytes/autograd/__init__.py

+from ._functions import undo_layout, get_inverse_transform_indices

bitsandbytes/autograd/_functions.py

@@ -2,6 +2,7 @@ import operator
 import warnings
 from dataclasses import dataclass
 from functools import reduce  # Required in Python 3
+from typing import Tuple, Optional
 
 import torch
 
@@ -14,6 +15,12 @@ def prod(iterable):
 
 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
@@ -48,6 +55,51 @@ class GlobalOutlierPooler:
         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):
@@ -171,6 +223,8 @@ matmul_cublas = MatMul8bit.apply
 
 @dataclass
 class MatmulLtState:
+    tile_indices: Optional[torch.Tensor] = None
+    force_no_igemmlt: bool = False
     CB = None
     CxB = None
     SB = None
@@ -202,11 +256,22 @@ class MatmulLtState:
         self.SBt = None
         self.CBt = None
 
+    def get_tile_size(self):
+        assert self.formatB in (
+            "col_turing",
+            "col_ampere",
+        ), f"please find this assert and manually enter tile size for {self.formatB}"
+        return (8, 32) if self.formatB == "col_turing" else (32, 32)
+
 
 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()):
-        # default to pytorch behavior if inputs are empty
+    def forward(ctx, A, B, out=None, bias=None, state=MatmulLtState):
+        using_igemmlt = torch.cuda.get_device_capability(device=A.device) >= (7, 5) 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
@@ -214,9 +279,9 @@ class MatMul8bitLt(torch.autograd.Function):
             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)
+                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)
+                return torch.empty(A.shape[:-1] + B.shape[:1], dtype=A.dtype, device=A.device)
 
         # 1. Quantize A
         # 2. Quantize B
@@ -235,9 +300,7 @@ class MatMul8bitLt(torch.autograd.Function):
         # 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
-        )
+        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:
@@ -248,12 +311,12 @@ class MatMul8bitLt(torch.autograd.Function):
                 state.subB = B[:, idx].t().contiguous()
                 state.idx = idx
             else:
-                if state.CxB is None:
+                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:
+            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
 
@@ -273,7 +336,10 @@ class MatMul8bitLt(torch.autograd.Function):
                     state.SCBt,
                     coo_tensorB,
                 ) = F.double_quant(B.to(torch.float16))
-                state.CxB, state.SB = F.transform(CB, to_order=formatB)
+                if using_igemmlt:
+                    state.CxB, state.SB = F.transform(CB, to_order=formatB)
+                else:
+                    state.CB = CB
         else:
             has_grad = False
 
@@ -288,18 +354,17 @@ class MatMul8bitLt(torch.autograd.Function):
             #    state.idx = state.outlier_pool.get_current_outlier_idx().to(A.device)
             # else:
             #    state.idx = outlier_idx
-            outliers = F.extract_outliers(state.CxB, state.SB, state.idx.int())
-            state.subB = (
-                (outliers * state.SCB.view(-1, 1) / 127.0)
-                .t()
-                .contiguous()
-                .to(A.dtype)
-            )
+            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]
+        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])
@@ -307,16 +372,25 @@ class MatMul8bitLt(torch.autograd.Function):
             output_shape = (input_shape[0], shapeB[0])
 
         # 3. Matmul
-        C32A, SA = F.transform(CA, "col32")
-        out32, Sout32 = F.igemmlt(C32A, state.CxB, SA, state.SB)
-        # we apply the fused bias here
+        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)
 
-        if bias is None or bias.dtype == torch.float16:
-            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:
@@ -337,14 +411,13 @@ class MatMul8bitLt(torch.autograd.Function):
             ctx.tensor_states = (None, None)
             ctx.save_for_backward(None, None)
 
-
-        clone_func = torch.clone if len(output_shape) == 3 else lambda x : x
+        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))
+            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 = ctx.tensors
@@ -359,9 +432,7 @@ class MatMul8bitLt(torch.autograd.Function):
 
         # Cast grad_output to fp16
         if len(grad_output.shape) == 3:
-            grad_output = grad_output.reshape(
-                -1, grad_output.shape[-1]
-            ).contiguous()
+            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:
@@ -376,17 +447,29 @@ class MatMul8bitLt(torch.autograd.Function):
             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
-                    )
+                    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. / 127.0))
+                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:
+
+                if state.tile_indices is None:
+                    order, tile_size = state.formatB, state.get_tile_size()
+                    transform = lambda x: F.transform(x.cuda(), from_order="row", to_order=order)[0].to(x.device)
+                    with torch.no_grad():
+                        state.tile_indices = get_inverse_transform_indices(transform, tile_size).to(state.CxB.device)
+
+                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 matrix for backward')
+                raise Exception("State must contain either CBt or CB or CxB matrix for backward")
 
         return grad_A, grad_B, None, grad_bias, None
 

bitsandbytes/cuda_setup/main.py

@@ -80,9 +80,10 @@ class CUDASetup:
         self.add_log_entry('python setup.py install')
 
     def initialize(self):
-        self.has_printed = False
-        self.lib = None
-        self.initialized = False
+        if not getattr(self, 'initialized', False):
+            self.has_printed = False
+            self.lib = None
+            self.initialized = False
 
     def run_cuda_setup(self):
         self.initialized = True
@@ -103,7 +104,7 @@ class CUDASetup:
                 legacy_binary_name = "libbitsandbytes_cpu.so"
                 self.add_log_entry(f"CUDA SETUP: Defaulting to {legacy_binary_name}...")
                 binary_path = package_dir / legacy_binary_name
-                if not binary_path.exists():
+                if not binary_path.exists() or torch.cuda.is_available():
                     self.add_log_entry('')
                     self.add_log_entry('='*48 + 'ERROR' + '='*37)
                     self.add_log_entry('CUDA SETUP: CUDA detection failed! Possible reasons:')
@@ -112,6 +113,7 @@ class CUDASetup:
                     self.add_log_entry('3. You have multiple conflicting CUDA libraries')
                     self.add_log_entry('4. Required library not pre-compiled for this bitsandbytes release!')
                     self.add_log_entry('CUDA SETUP: If you compiled from source, try again with `make CUDA_VERSION=DETECTED_CUDA_VERSION` for example, `make CUDA_VERSION=113`.')
+                    self.add_log_entry('CUDA SETUP: The CUDA version for the compile might depend on your conda install. Inspect CUDA version via `conda list | grep cuda`.')
                     self.add_log_entry('='*80)
                     self.add_log_entry('')
                     self.generate_instructions()
@@ -148,7 +150,7 @@ def is_cublasLt_compatible(cc):
     if cc is not None:
         cc_major, cc_minor = cc.split('.')
         if int(cc_major) < 7 or (int(cc_major) == 7 and int(cc_minor) < 5):
-            CUDASetup.get_instance().add_log_entry("WARNING: Compute capability < 7.5 detected! Proceeding to load CPU-only library...", is_warning=True)
+            CUDASetup.get_instance().add_log_entry("WARNING: Compute capability < 7.5 detected! Only slow 8-bit matmul is supported for your GPU!", is_warning=True)
         else:
             has_cublaslt = True
     return has_cublaslt
@@ -362,7 +364,6 @@ def evaluate_cuda_setup():
         print('')
         print('='*35 + 'BUG REPORT' + '='*35)
         print('Welcome to bitsandbytes. For bug reports, please submit your error trace to: https://github.com/TimDettmers/bitsandbytes/issues')
-        print('For effortless bug reporting copy-paste your error into this form: https://docs.google.com/forms/d/e/1FAIpQLScPB8emS3Thkp66nvqwmjTEgxp8Y9ufuWTzFyr9kJ5AoI47dQ/viewform?usp=sf_link')
         print('='*80)
     if not torch.cuda.is_available(): return 'libsbitsandbytes_cpu.so', None, None, None, None
 

bitsandbytes/nn/modules.py

@@ -209,19 +209,10 @@ class Int8Params(torch.nn.Parameter):
 
 
 class Linear8bitLt(nn.Linear):
-    def __init__(
-        self,
-        input_features,
-        output_features,
-        bias=True,
-        has_fp16_weights=True,
-        memory_efficient_backward=False,
-        threshold=0.0,
-        index=None,
-    ):
-        super().__init__(
-            input_features, output_features, bias
-        )
+    def __init__(self, input_features, output_features, bias=True, has_fp16_weights=True,
+                       memory_efficient_backward=False, threshold=0.0, index=None):
+        super().__init__(input_features, output_features, bias)
+        assert not memory_efficient_backward, "memory_efficient_backward is no longer required and the argument is deprecated in 0.37.0 and will be removed in 0.39.0"
         self.state = bnb.MatmulLtState()
         self.index = index
 
@@ -231,9 +222,7 @@ class Linear8bitLt(nn.Linear):
         if threshold > 0.0 and not has_fp16_weights:
             self.state.use_pool = True
 
-        self.weight = Int8Params(
-            self.weight.data, has_fp16_weights=has_fp16_weights, requires_grad=has_fp16_weights
-        )
+        self.weight = Int8Params(self.weight.data, has_fp16_weights=has_fp16_weights, requires_grad=has_fp16_weights)
 
     def init_8bit_state(self):
         self.state.CB = self.weight.CB
@@ -241,27 +230,20 @@ class Linear8bitLt(nn.Linear):
         self.weight.CB = None
         self.weight.SCB = None
 
-    def forward(self, x):
+    def forward(self, x: torch.Tensor):
         self.state.is_training = self.training
-
         if self.weight.CB is not None:
             self.init_8bit_state()
 
         # weights are cast automatically as Int8Params, but the bias has to be cast manually
-        if self.bias is not None and self.bias.dtype != torch.float16:
-            self.bias.data = self.bias.data.half()
+        if self.bias is not None and self.bias.dtype != x.dtype:
+            self.bias.data = self.bias.data.to(x.dtype)
 
         out = bnb.matmul(x, self.weight, bias=self.bias, state=self.state)
-
         if not self.state.has_fp16_weights:
-            if not self.state.memory_efficient_backward and self.state.CB is not None:
+            if self.state.CB is not None and self.state.CxB is not None:
                 # we converted 8-bit row major to turing/ampere format in the first inference pass
                 # we no longer need the row-major weight
                 del self.state.CB
                 self.weight.data = self.state.CxB
-            elif self.state.memory_efficient_backward and self.state.CxB is not None:
-                # For memory efficient backward, we convert 8-bit row major to turing/ampere format at each inference pass.
-                # Thus, we delete CxB from the state.
-                del self.state.CxB
-
         return out

setup.py

@@ -18,7 +18,7 @@ def read(fname):
 
 setup(
     name=f"bitsandbytes",
-    version=f"0.36.0-2",
+    version=f"0.37.0",
     author="Tim Dettmers",
     author_email="dettmers@cs.washington.edu",
     description="8-bit optimizers and matrix multiplication routines.",

tests/test_linear8bitlt.py

+import bitsandbytes as bnb
+import pytest
+import torch
+from bitsandbytes import functional as F
+
+from bitsandbytes.autograd import get_inverse_transform_indices, undo_layout
+from bitsandbytes.nn.modules import Linear8bitLt
+
+# contributed by Alex Borzunov, see:
+# https://github.com/bigscience-workshop/petals/blob/main/tests/test_linear8bitlt.py
+
+@pytest.mark.skipif(
+    not torch.cuda.is_available() or torch.cuda.get_device_capability() < (7, 5),
+    reason="this test requires a turing-generation or newer GPU, see bitsandbytes docs",
+)
+def test_layout_exact_match():
+    x = (torch.randn(14336 * 3, 14336) * 10).to(torch.int8).cuda()
+    for tile_size, order in ((8, 32), "col_turing"), ((32, 32), "col_ampere"):
+        transform = lambda x: F.transform(x.cuda(), from_order="row", to_order=order)[0].to(x.device)
+        tile_indices = get_inverse_transform_indices(transform, tile_size)
+        cxb = transform(x)
+
+        torch.cuda.synchronize()
+        restored_x = undo_layout(cxb, tile_indices)
+        torch.cuda.synchronize()
+        assert restored_x.is_contiguous()
+        assert torch.all(torch.eq(restored_x, x))
+
+@pytest.mark.skipif(not torch.cuda.is_available(), reason="this test requires a GPU")
+def test_linear_no_igemmlt():
+    linear = torch.nn.Linear(1024, 3072)
+    x = torch.randn(3, 1024, dtype=torch.half)
+    linear_custom = Linear8bitLt(
+        linear.in_features,
+        linear.out_features,
+        linear.bias is not None,
+        has_fp16_weights=False,
+        threshold=6.0,
+    )
+    linear_custom.state.force_no_igemmlt = True
+
+    linear_custom.weight = bnb.nn.Int8Params(
+        linear.weight.data.clone(), requires_grad=False, has_fp16_weights=False
+    ).to(linear.weight.dtype)
+    linear_custom.bias = linear.bias
+    linear = linear_custom.cuda()
+    linear = linear.half().cuda()
+
+    x_ref = x.clone().cuda().requires_grad_(True)
+    x_ours = x.clone().cuda().requires_grad_(True)
+    fx_ref = linear(x_ref).float()
+    grad_proj = torch.randn_like(fx_ref)
+    (fx_ref * grad_proj).mean().backward()
+
+    fx_ours = linear_custom(x_ours).float()
+    (fx_ours * grad_proj).mean().backward()
+    assert torch.allclose(fx_ref, fx_ours, atol=0.02)
+    assert torch.allclose(x_ref.grad, x_ours.grad, atol=0.01)
+    assert not linear_custom.state.has_fp16_weights
+    assert linear_custom.state.CB is not None
+    assert linear_custom.state.CxB is None

tests/test_modules.py

@@ -382,7 +382,7 @@ names = [f"threshold_{vals}" for vals in values]
 
 
 @pytest.mark.parametrize("threshold", values, ids=names)
-@pytest.mark.parametrize("memory_efficient_backward", [True, False])
+@pytest.mark.parametrize("memory_efficient_backward", [False])
 def test_linear8bitlt_no_fp16_weights(threshold, memory_efficient_backward):
     l1 = (
         bnb.nn.Linear8bitLt(