[DOCS] Matmul and vecadd working examples

This commit is contained in:
jack-willturner
2020-05-04 16:25:17 +01:00
committed by Philippe Tillet
parent ce4a4728f5
commit 32819dea51
6 changed files with 159 additions and 27 deletions

View File

@@ -3,7 +3,7 @@ Matrix Transpositions
*********************
Transpositions are (relatively) hard to efficiently write in CUDA because naive implementations typically suffer from *uncoalesced* memory operations when writing back the transposed matrix to DRAM.
Transpositions are (relatively) hard to efficiently write in CUDA because naive implementations typically suffer from *uncoalesced* memory operations when writing back the transposed matrix to DRAM.
Of course, this can be fixed by using shared memory as shown `here <https://devblogs.nvidia.com/efficient-matrix-transpose-cuda-cc>`_, but this comes at the cost of simplicity interferes with auto-tuning.
@@ -16,7 +16,7 @@ In Triton, however, kernels are single-threaded and the compiler automatically d
.. code-block:: C
// launched on a grid of (M / TM) x (N / TN) programs of 1 thread each
__global__ void transpose(TYPE * X, TYPE * Y,
__global__ void transpose(TYPE * X, TYPE * Y,
int M, int N, int ldx, int ldy) {
// extract program ID
int pidm = get_program_id(0); //(1)
@@ -30,7 +30,7 @@ In Triton, however, kernels are single-threaded and the compiler automatically d
// write back using the transposition operator '^'
*py = ^(*px); //(7)
}
At a high level, this kernel loads a :code:`TM x TN` tile from the input matrix :code:`X`, transposes it and writes the resulting :code:`TN x TM` tile to the output matrix :code:`Y`. Eventually, transposition of the full input matrix is achieved by launching a grid of :code:`(M / TM) x (N / TN)` programs decomposed as follows:
- Statements (1) and (2) extract the coordinates the program in the above 2D launch grid. For example, the program producing the output tile `Y[TN:2TN-1, 2TN:3TN-1]` holds the values:
@@ -54,7 +54,7 @@ which will be used in statements (5) and (6) to construct tiles of pointers
- Statements (5) constructs the following array of pointers `px` using numpy-style broadcasting semantics:
::
│ X + (pidm*TM + 0) + (pidn*TN + 0)*ldx, ..., ..., X + (pidm*TM + 0) + (pidn*TN + TN - 1)*ldx) │
│ ⋮ ⋮ │
│ ⋮ ⋮ │
@@ -83,19 +83,19 @@ For this reason, Triton provides a __multipleof(N) attributes for variables that
.. code-block:: C
__global__ void transpose(TYPE * X, TYPE * Y, int M, int N,
int ldx __multipleof(8),
__global__ void transpose(TYPE * X, TYPE * Y, int M, int N,
int ldx __multipleof(8),
int ldy __multipleof(8)) {
// ...
}
==========================
Bounds Checking
==========================
You might have noticed that the above code will fail when `M` and `N` are not multiples of `TM` and `TN` respectively. Fortunately, the above kernel can be slightly modified to handle thie situation, as shown below:
You might have noticed that the above code will fail when `M` and `N` are not multiples of `TM` and `TN` respectively. Fortunately, the above kernel can be slightly modified to handle this situation, as shown below:
.. code-block:: C
@@ -108,6 +108,6 @@ You might have noticed that the above code will fail when `M` and `N` are not mu
// conditional write-back using the conditional dereferencing operatior '*?()'
*?(checky)py = ^(*?(checkx)px); //(7)
}
Here, statements (7a) creates an array of booleans :code:`checkx[TM, TN]` such that :code:`checkx(i, j) = True` if and only if `px(i, j)` should be dereferenced. Statement (7b) does the same for `py`. Both `px` and `py` are then conditionally dereferenced using Triton-C's conditional dereferencing operator :code:`*?(predicate) pointer`.
Here, statements (7a) creates an array of booleans :code:`checkx[TM, TN]` such that :code:`checkx(i, j) = True` if and only if `px(i, j)` should be dereferenced. Statement (7b) does the same for `py`. Both `px` and `py` are then conditionally dereferenced using Triton-C's conditional dereferencing operator :code:`*?(predicate) pointer`.