diff --git a/ggml.h b/ggml.h index f92ae73..f352e71 100644 --- a/ggml.h +++ b/ggml.h @@ -1,5 +1,174 @@ #pragma once +// +// GGML Tensor Library +// +// This documentation is still a work in progress. +// If you wish some specific topics to be covered, feel free to drop a comment: +// +// https://github.com/ggerganov/whisper.cpp/issues/40 +// +// ## Overview +// +// This library implements: +// +// - a set of tensor operations +// - automatic differentiation +// - basic optimization algorithms +// +// The aim of this library is to provide a minimalistic approach for various machine learning tasks. This includes, +// but is not limited to, the following: +// +// - linear regression +// - support vector machines +// - neural networks +// +// The library allows the user to define a certain function using the available tensor operations. This function +// definition is represented internally via a computation graph. Each tensor operation in the function definition +// corresponds to a node in the graph. Having the computation graph defined, the user can choose to compute the +// function's value and/or its gradient with respect to the input variables. Optionally, the function can be optimized +// using one of the available optimization algorithms. +// +// For example, here we define the function: f(x) = a*x^2 + b +// +// { +// struct ggml_init_params params = { +// .mem_size = 16*1024*1024, +// .mem_buffer = NULL, +// }; +// +// // memory allocation happens here +// struct ggml_context * ctx = ggml_init(params); +// +// struct ggml_tensor * x = ggml_new_tensor_1d(ctx, GGML_TYPE_F32, 1); +// +// ggml_set_param(ctx, x); // x is an input variable +// +// struct ggml_tensor * a = ggml_new_tensor_1d(ctx, GGML_TYPE_F32, 1); +// struct ggml_tensor * b = ggml_new_tensor_1d(ctx, GGML_TYPE_F32, 1); +// struct ggml_tensor * x2 = ggml_mul(ctx, x, x); +// struct ggml_tensor * f = ggml_add(ctx, ggml_mul(ctx, a, x2), b); +// +// ... +// } +// +// Notice that the function definition above does not involve any actual computation. The computation is performed only +// when the user explicitly requests it. For example, to compute the function's value at x = 2.0: +// +// { +// ... +// +// struct ggml_cgraph gf = ggml_build_forward(f); +// +// // set the input variable and parameter values +// ggml_set_f32(x, 2.0f); +// ggml_set_f32(a, 3.0f); +// ggml_set_f32(b, 4.0f); +// +// ggml_graph_compute(ctx0, &gf); +// +// printf("f = %f\n", ggml_get_f32_1d(f, 0)); +// +// ... +// } +// +// The actual computation is performed in the ggml_graph_compute() function. +// +// The ggml_new_tensor_...() functions create new tensors. They are allocated in the memory buffer provided to the +// ggml_init() function. You have to be careful not to exceed the memory buffer size. Therefore, you have to know +// in advance how much memory you need for your computation. Alternatively, you can allocate a large enough memory +// and after defining the computation graph, call the ggml_used_mem() function to find out how much memory was +// actually needed. +// +// The ggml_set_param() function marks a tensor as an input variable. This is used by the automatic +// differentiation and optimization algorithms. +// +// The described approach allows to define the function graph once and then compute its forward or backward graphs +// multiple times. All computations will use the same memory buffer allocated in the ggml_init() function. This way +// the user can avoid the memory allocation overhead at runtime. +// +// The library supports multi-dimensional tensors - up to 4 dimensions. The FP16 and FP32 data types are first class +// citizens, but in theory the library can be extended to support FP8 and integer data types. +// +// Each tensor operation produces a new tensor. Initially the library was envisioned to support only the use of unary +// and binary operations. Most of the available operations fall into one of these two categories. With time, it became +// clear that the library needs to support more complex operations. The way to support these operations is not clear +// yet, but a few examples are demonstrated in the following operations: +// +// - ggml_permute() +// - ggml_conv_1d_1s() +// - ggml_conv_1d_2s() +// +// For each tensor operator, the library implements a forward and backward computation function. The forward function +// computes the output tensor value given the input tensor values. The backward function computes the adjoint of the +// input tensors given the adjoint of the output tensor. For a detailed explanation of what this means, take a +// calculus class, or watch the following video: +// +// What is Automatic Differentiation? +// https://www.youtube.com/watch?v=wG_nF1awSSY +// +// +// ## Tensor data (struct ggml_tensor) +// +// The tensors are stored in memory via the ggml_tensor struct. The structure provides information about the size of +// the tensor, the data type, and the memory buffer where the tensor data is stored. Additionally, it contains +// pointers to the "source" tensors - i.e. the tensors that were used to compute the current tensor. For example: +// +// { +// struct ggml_tensor * c = ggml_add(ctx, a, b); +// +// assert(c->src[0] == a); +// assert(c->src[1] == b); +// } +// +// The multi-dimensional tensors are stored in row-major order. The ggml_tensor struct contains fields for the +// number of elements in each dimension ("ne") as well as the number of bytes ("nb", a.k.a. stride). This allows +// to store tensors that are not contiguous in memory, which is useful for operations such as transposition and +// permutation. All tensor operations have to take the stride into account and not assume that the tensor is +// contiguous in memory. +// +// The data of the tensor is accessed via the "data" pointer. For example: +// +// { +// struct ggml_tensor * a = ggml_new_tensor_2d(ctx, GGML_TYPE_F32, 2, 3); +// +// // a[1, 2] = 1.0f; +// *(float *) ((char *) a->data + 2*a->nb[1] + 1*a->nb[0]) = 1.0f; +// +// // a[2, 0] = 2.0f; +// *(float *) ((char *) a->data + 0*a->nb[1] + 2*a->nb[0]) = 2.0f; +// +// ... +// } +// +// Alternatively, there are helper functions, such as ggml_get_f32_1d() and ggml_set_f32_1d() that can be used. +// +// ## The matrix multiplication operator (ggml_mul_mat) +// +// TODO +// +// +// ## Multi-threading +// +// TODO +// +// +// ## Overview of ggml.c +// +// TODO +// +// +// ## SIMD optimizations +// +// TODO +// +// +// ## Debugging ggml +// +// TODO +// +// + #ifdef __cplusplus extern "C" { #endif @@ -21,7 +190,8 @@ typedef __fp16 ggml_fp16_t; typedef uint16_t ggml_fp16_t; #endif -float ggml_fp16_to_fp32(ggml_fp16_t x); +// convert FP16 <-> FP32 +float ggml_fp16_to_fp32(ggml_fp16_t x); ggml_fp16_t ggml_fp32_to_fp16(float x); struct ggml_object; @@ -36,6 +206,7 @@ enum ggml_type { GGML_TYPE_COUNT, }; +// available tensor operations: enum ggml_op { GGML_OP_NONE = 0, @@ -136,7 +307,7 @@ struct ggml_init_params { void * mem_buffer; // if NULL, memory will be allocated internally }; -void ggml_time_init(void); +void ggml_time_init(void); // call this once at the beginning of the program int64_t ggml_time_ms(void); int64_t ggml_time_us(void); int64_t ggml_cycles(void);