CUDA Academy · 강의

device와 host 함수

각 종류의 함수가 실행될 수 있는 위치를 알아봅니다.

__device__와 __host__ 함수은(는) CoddyKit의 무료 CUDA Academy 강의입니다. 이것은 4개 중 2번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 CUDA Academy 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. CUDA Academy 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Beyond the Kernel

Kernels are entry points, but most code lives in helpers. CUDA gives two more qualifiers to say where a plain function may run. Let us meet them.

The device Qualifier

A __device__ function runs on the GPU and is callable only from other GPU code, like a kernel or another device function.

__device__ int square(int x) {
    return x * x;
}

Helpers for Kernels

Think of __device__ functions as your GPU toolbox. They keep kernels tidy by holding logic the device threads reuse.

The host Qualifier

The __host__ qualifier means ordinary CPU code. It is the default, so plain C++ functions are already host functions.

__host__ void setup() {
    // runs on the CPU
}

Default Is Host

Leave off all qualifiers and your function is host-only by default. That is why normal C++ still compiles inside a .cu file.

Both at Once

Combine the two and a function compiles for both sides. nvcc builds one version for the CPU and one for the GPU.

__host__ __device__ int dbl(int x) {
    return x + x;
}

Why Dual-Compile?

Marking a helper __host__ __device__ lets the same math run in CPU reference code and inside kernels, with zero duplication. ✨

Calling Rules

Host code may not call a __device__ function, and device code may not call a host-only one. The compiler enforces the boundary.

No global from Device

A __device__ function is not launchable. Only __global__ kernels accept the triple-angle-bracket launch from the host.

Inlining for Speed

The compiler often inlines small __device__ functions, so wrapping logic in helpers usually costs nothing at runtime.

Pick the Right Tag

Choose by where it runs: __device__ for GPU helpers, __host__ for CPU code, and both when the logic is shared.

Quick Check

Time to test the device and host qualifiers.

Recap

You learned __device__ runs on the GPU, __host__ runs on the CPU, the default is host, and combining both shares one function across worlds. 🎯

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