大型並行處理程式設計：實務導向教學：超越一維陣列：擴展至多維資料

歡迎來到 偉大的轉移。在中央處理器（CPU）程式設計中，我們定義如何進行迭代；而在通用圖形處理單元（GPGPU）中，我們定義什麼一次迭代的樣貌。這種從以指令為中心轉向以資料為中心的邏輯轉變，是由 核心抽象所驅動。

透過使用 __global__ 修飾符，你並非撰寫一個函數——你是在設計一個 可擴展的藍圖。單一的核心執行代表一個獨立的工作單元，讓顯示處理器（GPU）能在其龐大的核心數量下，無需手動管理線程，便能協調成千上萬個相同任務。

在百萬個線程中，單一線程如何找到目標？它使用一種稱為索引公式的確定性契約：

$$\text{threadID} = \text{blockIdx.x} \times \text{blockDim.x} + \text{threadIdx.x}$$

此公式如同一個座標系統，將軟體的邏輯資料（陣列）與硬體的物理階層（區塊與線程）連結起來。

這些 <<<B, T>>> 參數定義了網格形狀。這確保了 透明可擴展性：無論硬體擁有 2 個流式多處理器（SM）或 80 個，你的程式碼都能執行相同的邏輯。

TERMINALbash — 80x24

> Ready. Click "Run" to execute.

QUESTION 1

What is the primary role of the __global__ qualifier?

To define a function that runs on the CPU and is called by the GPU.

To mark a function as a kernel that is callable from the host and executes on the device.

To synchronize all threads across the entire GPU grid.

To allocate memory in the global memory space.

QUESTION 2

If blockIdx.x = 2, blockDim.x = 256, and threadIdx.x = 10, what is the global index?

266

512

522

778

QUESTION 3

What does 'Transparent Scalability' imply in CUDA?

The memory automatically scales with the size of the input array.

The same code can run on different GPUs with varying SM counts without modification.

Threads can see into the registers of other threads.

The kernel speed increases linearly with the clock speed of the CPU.

QUESTION 4

Why is the if (i < n) check necessary in a kernel?

To prevent the GPU from overheating.

To ensure threads do not access memory outside the valid array bounds.

To check if the kernel is running on the correct SM.

To synchronize memory access between threads.

QUESTION 5

Which variable represents the number of threads within a single block?

gridDim.x

blockIdx.x

blockDim.x

threadIdx.x