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101 lines
3.1 KiB
Markdown
101 lines
3.1 KiB
Markdown
# GPU Implementation Strategy
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## Overview
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This document outlines the GPU implementation strategy for MetalOS targeting the AMD Radeon RX 6600 (RDNA2 / Navi 23 architecture).
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## Reality Check: Where the Bloat Really Lives (RDNA2)
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On Navi 23, you will not get good performance without:
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- GPU firmware blobs (various `dimgrey_cavefish_*.bin` files; Navi 23's codename is "dimgrey cavefish", and Linux systems load firmware files with that prefix)
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- A real memory manager (VRAM/GTT, page tables, buffer objects)
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- Command submission (rings/queues) + fences/semaphores
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- A Vulkan driver implementation (or reuse one)
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So the "least bloat" strategy is: reuse a Vulkan implementation (Mesa RADV is the obvious candidate), but avoid importing a whole Unix stack by giving it a very small kernel/userspace interface tailored to your OS.
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RADV is explicitly a userspace Vulkan driver for modern AMD GPUs.
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---
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## The Best "Toy OS but Fast" Plan: RADV + a Tiny amdgpu-shaped Shim
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### Why This is the Sweet Spot
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- You keep your OS non-POSIX
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- You avoid writing a Vulkan driver from scratch (the truly hard part)
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- You implement only the kernel-facing parts RADV needs: a buffer object + VM + submit + sync API
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### Shape of the Stack
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**MetalOS Kernel:**
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- PCIe enumeration, BAR mapping
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- Interrupts (MSI/MSI-X)
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- DMA mapping (or identity-map if you're being reckless)
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- A GPU kernel driver that exposes a small ioctl-like API
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**Userspace:**
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- `gpu-service` (optional but recommended for structure)
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- `libradv-metal` (a minimal libdrm-like bridge)
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- Mesa RADV compiled against your bridge (not Linux libdrm)
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This is "Unix-like internally" only in the sense of interfaces, not user experience.
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---
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## Minimal Kernel GPU API (The Smallest Set That Still Performs)
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Think in terms of four pillars:
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### A) Firmware Load + ASIC Init
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```c
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gpu_load_firmware(name, blob)
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gpu_init() → returns chip info (gfx1032, VRAM size, doorbells, etc.)
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```
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You will need those Navi23 firmware blobs (again: `dimgrey_cavefish_*.bin` family is the practical breadcrumb).
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### B) Buffer Objects (BOs)
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```c
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bo_create(size, domain=VRAM|GTT, flags)
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bo_map(bo) / bo_unmap(bo) // CPU mapping
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bo_export_handle(bo) // so Vulkan can bind memory
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```
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### C) Virtual Memory (GPU Page Tables)
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```c
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vm_create()
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vm_map(vm, bo, gpu_va, size, perms)
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vm_unmap(vm, gpu_va, size)
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```
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### D) Submission + Synchronization
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```c
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queue_create(type=GFX|COMPUTE|DMA)
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queue_submit(queue, cs_buffer, fence_out)
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fence_wait(fence, timeout)
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timeline_semaphore_* // optional, but hugely useful
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```
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If you implement these correctly, you get real GPU throughput.
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---
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## Implementation Notes
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- Focus on the minimal API surface that RADV requires
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- Firmware blobs are non-negotiable for Navi 23 performance
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- Memory management (VRAM/GTT) is critical for proper GPU operation
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- Command submission infrastructure must be solid for reliability
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- Synchronization primitives (fences/semaphores) enable proper GPU-CPU coordination
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## References
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- Mesa RADV driver source code
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- AMD GPU specifications for RDNA2 architecture
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- Linux amdgpu kernel driver for reference implementation patterns
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