feat: rewrite about page for 2026. (#21)

Signed-off-by: jackfiled <xcrenchangjun@outlook.com>
Reviewed-on: #21

source/posts/hpc-2025-opencl.md

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+---
+title: High Performance Computing 25 SP OpenCL Programming
+date: 2025-08-31T13:51:02.0181970+08:00
+tags:
+- 高性能计算
+- 学习资料
+---
+
+
+Open Computing Language.
+
+<!--more-->
+
+OpenCL is Open Computing Language.
+
+- Open, royalty-free standard C-language extension.
+- For parallel programming of heterogeneous systems using GPUs, CPUs , CBE, DSP and other processors including embedded mobile devices.
+- Managed by Khronos Group.
+
+![image-20250529185915068](./hpc-2025-opencl/image-20250529185915068.webp)
+
+### Anatomy of OpenCL
+
+- Platform Layer APi
+- Runtime Api
+- Language Specification
+
+### Compilation Model
+
+OpenCL uses dynamic/runtime compilation model like OpenGL.
+
+1. The code is compiled to an IR.
+2. The IR is compiled to a machine code for execution.
+
+And in dynamic compilation, *step 1* is done usually once and the IR is stored. The app loads the IR and performs *step 2* during the app runtime.
+
+### Execution Model
+
+OpenCL program is divided into
+
+- Kernel: basic unit of executable code.
+- Host: collection of compute kernels and internal functions.
+
+The host program invokes a kernel over an index space called an **NDRange**.
+
+NDRange is *N-Dimensional Range*, and can be a 1, 2, 3-dimensional space.
+
+A single kernel instance at a point of this index space is called **work item**. Work items are further grouped into **work groups**.
+
+### OpenCL Memory Model
+
+![image-20250529191215424](./hpc-2025-opencl/image-20250529191215424.webp)
+
+Multiple distinct address spaces: Address can be collapsed depending on the device's memory subsystem.
+
+Address space:
+
+- Private: private to a work item.
+- Local: local to a work group.
+- Global: accessible by all work items in all work groups.
+- Constant: read only global memory.
+
+> Comparison with CUDA:
+>
+> ![image-20250529191414250](./hpc-2025-opencl/image-20250529191414250.webp)
+
+Memory region for host and kernel:
+
+![image-20250529191512490](./hpc-2025-opencl/image-20250529191512490.webp)
+
+### Programming Model
+
+#### Data Parallel Programming Model
+
+1. Define N-Dimensional computation domain
+2. Work-items can be grouped together as *work group*.
+3. Execute multiple work-groups in parallel.
+
+#### Task Parallel Programming Model
+
+> Data parallel execution model must be implemented by all OpenCL computing devices, but task parallel programming is a choice for vendor.
+
+Some computing devices such as CPUs can also execute task-parallel computing kernels.
+
+- Executes as s single work item.
+- A computing kernel written in OpenCL.
+- A native function.
+
+### OpenCL Framework 
+
+![image-20250529192022613](./hpc-2025-opencl/image-20250529192022613.webp)
+
+The basic OpenCL program structure:
+
+![image-20250529192056388](./hpc-2025-opencl/image-20250529192056388.webp)
+
+**Contexts** are used to contain the manage the state of the *world*.
+
+**Command-queue** coordinates execution of the kernels.
+