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Printing with CuTe DSL

examples/python/CuTeDSL/notebooks/print.ipynb

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Printing with CuTe DSL

This notebook demonstrates the different ways to print values in CuTe and explains the important distinction between static (compile-time) and dynamic (runtime) values.

Key Concepts

  • Static values: Known at compile time
  • Dynamic values: Only known at runtime
  • Different printing methods for different scenarios
  • Layout representation in CuTe
  • Tensor visualization and formatting
python
import cutlass
import cutlass.cute as cute
import numpy as np

The print_example function demonstrates several important concepts:

1. Python's print vs CuTe's cute.printf

  • print: Can only show static values at compile time
  • cute.printf: Can display both static and dynamic values at runtime

2. Value Types

  • a: Dynamic Int32 value (runtime)
  • b: Static Constexpr[int] value (compile-time)

3. Layout Printing

Shows how layouts are represented differently in static vs dynamic contexts:

  • Static context: Unknown values shown as ?
  • Dynamic context: Actual values displayed
python
@cute.jit
def print_example(a: cutlass.Int32, b: cutlass.Constexpr[int]):
    """
    Demonstrates different printing methods in CuTe and how they handle static vs dynamic values.

    This example shows:
    1. How Python's `print` function works with static values at compile time but can't show dynamic values
    2. How `cute.printf` can display both static and dynamic values at runtime
    3. The difference between types in static vs dynamic contexts
    4. How layouts are represented in both printing methods

    Args:
        a: A dynamic Int32 value that will be determined at runtime
        b: A static (compile-time constant) integer value
    """
    # Use Python `print` to print static information
    print(">>>", b)  # => 2
    # `a` is dynamic value
    print(">>>", a)  # => ?

    # Use `cute.printf` to print dynamic information
    cute.printf(">?? {}", a)  # => 8
    cute.printf(">?? {}", b)  # => 2

    print(">>>", type(a))  # => <class 'cutlass.Int32'>
    print(">>>", type(b))  # => <class 'int'>

    layout = cute.make_layout((a, b))
    print(">>>", layout)  # => (?,2):(1,?)
    cute.printf(">?? {}", layout)  # => (8,2):(1,8)

Compile and Run

Direct Compilation and Run

  • print_example(cutlass.Int32(8), 2)
  • Compiles and runs in one step will execute both static and dynamic print
    • >>> stands for static print
    • >?? stands for dynamic print
python
print_example(cutlass.Int32(8), 2)

Compile Function

When compiles the function with cute.compile(print_example, cutlass.Int32(8), 2), Python interpreter traces code and only evaluate static expression and print static information.

python
print_example_compiled = cute.compile(print_example, cutlass.Int32(8), 2)

Call compiled function

Only print out runtime information

python
print_example_compiled(cutlass.Int32(8))

Format String Example

The format_string_example function shows an important limitation:

  • F-strings in CuTe are evaluated at compile time
  • This means dynamic values won't show their runtime values in f-strings
  • Use cute.printf when you need to see runtime values
python
@cute.jit
def format_string_example(a: cutlass.Int32, b: cutlass.Constexpr[int]):
    """
    Format string is evaluated at compile time.
    """
    print(f"a: {a}, b: {b}")

    layout = cute.make_layout((a, b))
    print(f"layout: {layout}")


print("Direct run output:")
format_string_example(cutlass.Int32(8), 2)

Printing Tensor Examples

CuTe provides specialized functionality for printing tensors through the print_tensor operation. The cute.print_tensor takes the following parameter:

  • Tensor (required): A CuTe tensor object that you want to print. The tensor must support load and store operations
  • verbose (optional, default=False): A boolean flag that controls the level of detail in the output. When set to True, it will print indices details for each element in the tensor.

Below example code shows the difference between verbose ON and OFF, and how to print a sub range of the given tensor.

python
from cutlass.cute.runtime import from_dlpack


@cute.jit
def print_tensor_basic(x: cute.Tensor):
    # Print the tensor
    print("Basic output:")
    cute.print_tensor(x)


@cute.jit
def print_tensor_verbose(x: cute.Tensor):
    # Print the tensor with verbose mode
    print("Verbose output:")
    cute.print_tensor(x, verbose=True)


@cute.jit
def print_tensor_slice(x: cute.Tensor, coord: tuple):
    # slice a 2D tensor from the 3D tensor
    sliced_data = cute.slice_(x, coord)
    y = cute.make_rmem_tensor(sliced_data.layout, sliced_data.element_type)
    # Convert to TensorSSA format by loading the sliced data into the fragment
    y.store(sliced_data.load())
    print("Slice output:")
    cute.print_tensor(y)

The default cute.print_tensor will output CuTe tensor with datatype, storage space, CuTe layout information, and print data in torch-style format.

python
def tensor_print_example1():
    shape = (4, 3, 2)

    # Creates [0,...,23] and reshape to (4, 3, 2)
    data = np.arange(24, dtype=np.float32).reshape(*shape)

    print_tensor_basic(from_dlpack(data))


tensor_print_example1()

The verbosed print will show coodination details of each element in the tensor. The below example shows how we index element in a 2D 4x3 tensor space.

python
def tensor_print_example2():
    shape = (4, 3)

    # Creates [0,...,11] and reshape to (4, 3)
    data = np.arange(12, dtype=np.float32).reshape(*shape)

    print_tensor_verbose(from_dlpack(data))


tensor_print_example2()

To print a subset elements in the given Tensor, we can use cute.slice_ to select a range of the given tensor, load them into register and then print the values with cute.print_tensor.

python
def tensor_print_example3():
    shape = (4, 3)

    # Creates [0,...,11] and reshape to (4, 3)
    data = np.arange(12, dtype=np.float32).reshape(*shape)

    print_tensor_slice(from_dlpack(data), (None, 0))
    print_tensor_slice(from_dlpack(data), (1, None))


tensor_print_example3()

To print the tensor in device memory, you can use cute.print_tensor within CuTe JIT kernels.

python
@cute.kernel
def print_tensor_gpu(src: cute.Tensor):
    print(src)
    cute.print_tensor(src)


@cute.jit
def print_tensor_host(src: cute.Tensor):
    print_tensor_gpu(src).launch(grid=(1, 1, 1), block=(1, 1, 1))
python
import torch


def tensor_print_example4():
    a = torch.randn(4, 3, device="cuda")
    cutlass.cuda.initialize_cuda_context()
    print_tensor_host(from_dlpack(a))


tensor_print_example4()

Currently, cute.print_tensor only supports tensor with integer data types and Float16/Float32/Float64 floating point data types. We will support more data types in the future.