Add fused bias linear layer with cublaslt (#400)

* Add fused bias linear layer with cublaslt

* Setup cublaslt

* Format and fix bs dim

* Improve test case

* Add arange test

mistralrs-core/src/layers.rs

@@ -12,7 +12,7 @@ use std::{
 
 use candle_core::{
     quantized::{gguf_file, QMatMul, QTensor},
-    DType, Device, IndexOp, Result, Tensor,
+    DType, Device, IndexOp, Result, Shape, Tensor, D,
 };
 use candle_nn::{Linear, Module, VarBuilder};
 use either::Either;
@@ -398,6 +398,57 @@ impl ScaledDotProductAttention {
     }
 }
 
+/// Linear layer with fused bias matmul.
+#[derive(Debug)]
+pub struct FusedBiasLinear {
+    pub(crate) w: Tensor,
+    pub(crate) b: Tensor,
+}
+
+impl TryFrom<Linear> for FusedBiasLinear {
+    type Error = candle_core::Error;
+
+    fn try_from(x: Linear) -> Result<Self> {
+        if let Some(bias) = x.bias() {
+            Ok(Self {
+                w: x.weight().clone(),
+                b: bias.clone(),
+            })
+        } else {
+            candle_core::bail!("`FusedBiasLinear` expects a Linear layer with bias.")
+        }
+    }
+}
+
+impl Module for FusedBiasLinear {
+    fn forward(&self, x: &Tensor) -> Result<Tensor> {
+        let w = match *x.dims() {
+            [b1, b2, _, _] => self.w.broadcast_left((b1, b2))?,
+            [bsize, _, _] => self.w.broadcast_left(bsize)?,
+            _ => self.w.clone(),
+        };
+        let mut tgt_shape = x.dims().to_vec();
+        tgt_shape[x.dims().len() - 1] = w.dim(D::Minus2)?;
+        let b = self.b.broadcast_as(Shape::from_dims(&tgt_shape))?;
+
+        if let (Device::Cuda(_), Some(cublaslt)) = (x.device(), *CUBLASLT_HANDLE.lock().unwrap()) {
+            cublaslt
+                .batch_matmul(
+                    x,
+                    &w,
+                    Some(&b.t()?.contiguous()?),
+                    None,
+                    Some(1.0),
+                    None,
+                    None,
+                )?
+                .t()
+        } else {
+            x.matmul(&w.t()?)? + b
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct QLinear {
     inner: QMatMul,
@@ -493,3 +544,78 @@ impl Module for QLinear {
         }
     }
 }
+
+mod tests {
+
+    #[test]
+    fn fused_bias_linear() {
+        use candle_core::{DType, Device, IndexOp, Tensor};
+        use candle_nn::{Linear, Module};
+
+        use crate::cublaslt::setup_cublas_lt_wrapper;
+        use crate::layers::FusedBiasLinear;
+
+        const IN: usize = 1921;
+        const OUT: usize = 4096;
+        const INNER: usize = 1024;
+
+        let dev = Device::cuda_if_available(0).unwrap();
+        setup_cublas_lt_wrapper();
+
+        let inner_dtype = if dev.is_cuda() {
+            DType::BF16
+        } else {
+            DType::F32
+        };
+
+        let w = Tensor::arange(0f32, (OUT * IN) as f32, &dev)
+            .unwrap()
+            .to_dtype(inner_dtype)
+            .unwrap()
+            .reshape((OUT, IN))
+            .unwrap();
+        let b = Tensor::arange(0f32, OUT as f32, &dev)
+            .unwrap()
+            .to_dtype(inner_dtype)
+            .unwrap()
+            .reshape((OUT,))
+            .unwrap();
+
+        let xs = Tensor::arange(0f32, (INNER * IN) as f32, &dev)
+            .unwrap()
+            .to_dtype(inner_dtype)
+            .unwrap()
+            .reshape((1, INNER, IN))
+            .unwrap();
+
+        let lin = Linear::new(w.clone(), Some(b.clone()));
+        let truth_out = lin.forward(&xs).unwrap();
+        let truth_y = truth_out
+            .to_dtype(DType::F32)
+            .unwrap()
+            .to_vec3::<f32>()
+            .unwrap();
+
+        let fused = FusedBiasLinear { w, b };
+        let fused_out = fused.forward(&xs).unwrap();
+        let fused_y = fused_out
+            .to_dtype(DType::F32)
+            .unwrap()
+            .to_vec3::<f32>()
+            .unwrap();
+
+        assert_eq!(truth_out.shape(), fused_out.shape());
+        if truth_y != fused_y {
+            panic!(
+                "Truth does not match fused kernel. Diff fused - truth:\n{:#?}",
+                &(&fused_out - &truth_out)
+                    .unwrap()
+                    .i((0, 5..10, 0..5))
+                    .unwrap()
+                    .to_dtype(DType::F32)
+                    .unwrap()
+                    .to_vec2::<f32>()
+            )
+        }
+    }
+}