Added matmul_mixed.

bitsandbytes/__init__.py

@@ -10,7 +10,8 @@ from .autograd._functions import (
     matmul,
     matmul_cublas,
     mm_cublas,
-    matmul_fp8
+    matmul_fp8,
+    matmul_mixed
 )
 from .cextension import COMPILED_WITH_CUDA
 from .nn import modules

bitsandbytes/autograd/_functions.py

@@ -461,6 +461,190 @@ class MatMulFP8(torch.autograd.Function):
         return grad_A, grad_B, None, None, None
 
 
+class MatMul8bitMixed(torch.autograd.Function):
+    @staticmethod
+    def forward(ctx, A, B, out=None, bias=None, state=MatmulLtState()):
+        # default to 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:
+                    # 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:
+                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))
+                state.CxB, state.SB = F.transform(CB, to_order=formatB)
+        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
+            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)
+            )
+            CA[:, state.idx.long()] = 0
+            CAt[:, state.idx.long()] = 0
+            subA = A[:, state.idx.long()]
+
+        shapeB = state.SB[0]
+
+        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
+        C32A, SA = F.transform(CA, "col32")
+        out32, Sout32 = F.igemmlt(C32A, state.CxB, SA, state.SB)
+        # we apply the fused bias here
+
+        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)
+
+        # 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, None]
+            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:
+            grad_B = torch.matmul(grad_output.t(), A)
+
+        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. / 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')
+
+        return grad_A, grad_B, None, grad_bias, None
+
+
 def matmul(
     A: tensor,
     B: tensor,
@@ -479,7 +663,7 @@ def matmul_fp8(A: tensor, B: tensor, fw_code: tensor, bw_code: tensor, out: tens
     return MatMulFP8.apply(A, B, out, fw_code, bw_code)
 
 
-def matmul(
+def matmul_mixed(
     A: tensor,
     B: tensor,
     out: tensor = None,
@@ -490,4 +674,4 @@ def matmul(
     state = state or MatmulLtState()
     if threshold > 0.0:
         state.threshold = threshold
-    return MatMul8bitLt.apply(A, B, out, bias, state)
+    return MatMul8bitMixed.apply(A, B, out, bias, state)

tests/test_autograd.py

@@ -239,7 +239,7 @@ dim4 = torch.randint(32, 96, size=(n,)).tolist()
 dim2.append(0)
 
 decomp = [0.0, 6.0]
-funcs = [(torch.matmul, bnb.matmul)]
+funcs = [(torch.matmul, bnb.matmul_mixed)]
 str_funcs = ["matmul"]
 req_grad = [(False, False), (True, False), (True, True), (False, True)]
 req_grad = list(product([True, False], repeat=3))