---
name: amd-apu-vulkan-tenant-onboarding
description: "Add a ggml/Vulkan inference tenant to an AMD APU (gfx1151 / Strix Halo iGPU) that already serves another engine: APU memory census, RADV heap gate, render-node resolution, build-side glslc/ICD deps, co-tenancy measurement."
---

Use when a ggml-based engine (llama.cpp, qwentts.cpp, anything built on ggml) must move from CPU to the **iGPU** of an AMD APU (gfx1151 / Strix Halo / Ryzen AI Max) that **already serves another engine on the same card**. Answers two questions only a booted host can: what gate the second tenant must clear, and which files the build needs to clear it.

## 1. The usual VRAM reasoning is wrong on an APU

`/sys/class/drm/cardN/device/mem_info_vram_total` reports a small **carve-out** (2 GiB class), and `rocm-smi`'s "dedicated" figure is not the working set either. The real working set lives in **GTT / system pages**: `/proc/meminfo` → `GTT` and `System pages`. A second GPU tenant therefore consumes host RAM from the same pool the first tenant's weights and the OS use — no supplementary groups, no separate aperture to reserve.

- Price the tenant from a **booted** footprint, never from `weights + KV + buffers`: on an APU the compute buffers and any projector ride on GTT, which is host RAM; check `free` *after* the load, not before.
- Never subtract a "dedicated" figure from it to find headroom.
- Unheld fabric clock (`pp_dpm_mech` = `auto`) is a hazard only when the NPU joins too; a pure iGPU pair is unaffected — check it before adding a third tenant.
- Swap on a host with GPU tenants protects co-tenants; paging a KV pool is worse than the OOM it prevents.

## 2. The gate that decides feasibility: the RADV heap a container sees

`rocm-smi` and `free` cannot see this number; only a container off the **engine's own base image** can:

```bash
# one-off container, no model, no load, no compute — safe beside production
podman run --rm --device /dev/dri --group-add keep-groups <engine-base> bash -c \
  'apt-get update -qq >/dev/null 2>&1; apt-get install -y -qq --no-install-recommends mesa-vulkan-drivers vulkan-tools glslang-tools >/dev/null 2>&1; vulkaninfo --text'
```

Read `VkPhysicalDeviceMemoryProperties` → the `DEVICE_LOCAL` heap size. On a hybrid Strix Halo box Mesa splits the aperture (~1/3 : 2/3), so `DEVICE_LOCAL` is the budget the ggml tool will actually allocate against — measured 77.33 GiB *with the first tenant loaded*, against a 2 GiB DRM carve-out. Two traps, both measured:

- `vulkaninfo --batch` does not exist in Ubuntu 24.04's `vulkan-tools` (prints help, exits 1). Every `vulkaninfo` parse needs `--text`.
- The container may have **no NVIDIA ICD**, so Vulkan index `0` *is* the iGPU — but do not trust ordering by index: `--text` and read `deviceName` + `driverID` (`RADV_GFX1151` vs `NVIDIA`). A hand-picked `/dev/dri/renderDN` is worse than useless on a hybrid host: **`renderD128` there is the NVIDIA card and `renderD129` the amdgpu iGPU**; resolve the node with `readlink -f /sys/class/drm/renderD*/device/driver` and pass `/dev/dri` wholesale, letting the driver pick by name.
- A rootless container that drops its supplementary groups enumerates **nothing**. `--group-add keep-groups` (quadlet: `GroupAdd=keep-groups`) plus the host udev rule that makes the render nodes group-writable is the whole requirement; `--device /dev/dri` alone is not enough.

## 3. Build-side deps: the configure fails before the device ever matters

ggml's `src/ggml-vulkan/CMakeLists.txt` requires, in order: `find_package(Vulkan COMPONENTS glslc REQUIRED)` then `find_package(SPIRV-Headers CONFIG REQUIRED)`, and it compiles its shaders with **glslc**, never `glslangValidator`. On Ubuntu 24.04 (measured against the digest-pinned `ubuntu:24.04` base, 2026-10-19):

- `glslang-tools` ships `glslangValidator` and **NOT `glslc`** → `command -v glslc` empty, `find_package(Vulkan … glslc REQUIRED)` fails, and the Vulkan backend silently never exists.
- The package is the standalone **`glslc`** (universe, `2023.8-1build1`). Working build-stage set: `libvulkan-dev glslc spirv-headers` — `libvulkan-dev` provides `vulkan/vulkan.h` + the `VulkanHeaders`/`VulkanLoader` CMake configs `find_package(Vulkan)` resolves to, `spirv-headers` ships `/usr/share/cmake/SPIRV-Headers/SPIRV-HeadersConfig.cmake`. A configure probe in the pinned base prints `Found Vulkan: … found components: glslc` then `Including Vulkan backend`.
- **The archive's glslc is old.** 2023.8 compiles `GL_KHR_cooperative_matrix` (the path ggml's vectored quantized matmul needs) but reports `cooperative_matrix2`, `integer_dot_product`, `bfloat16`, `float_e2m1/e4m3` as unsupported, so those shader families are compiled out. If a Vulkan prefill reads as inexplicably slow, suspect the **shader compiler before the device**; the fix is a pinned glslang build passed as `-DVulkan_GLSLC_EXECUTABLE=<path>`, not a different runtime.
- Runtime stage needs the loader **and an ICD**: `libvulkan1` + `mesa-vulkan-drivers`. Loader-without-ICD enumerates zero devices, and ggml-based servers die in device lookup — often *after* reading the weights, so the journal reads like a model fault.
- Ship **no NVIDIA ICD** on purpose: one Vulkan device in the enumeration is what makes the *name* `Vulkan0` safe to write into config. Prefer the name over an index in every flag.

## 4. Prove enumeration without allocating anything

Do not boot a scratch second engine beside production to ask which devices exist — a second model load is a real GPU tenant, and fleet law stops that. Instead run the binary with a device name that cannot exist and read its error; it names what it enumerated, with no allocation and no model resident:

```bash
podman run --rm --device /dev/dri --group-add keep-groups --entrypoint /app/tts-server <image> \
  --model /dev/null --codec /dev/null --device NoSuchDevice 2>&1 | tail -20
```

## 5. The rollback must be a flag, not a rebuild

Put the device in the env file as a value the entrypoint passes only when set, and make **set-but-empty** mean "pass no flag at all" — the binary's own default (CPU, always built) is the rollback. `: "${VAR:=default}"` is the WRONG form: `:=` fires on an empty value too, so the documented rollback line `VAR=` is silently rewritten back to the GPU and the only way out is a rebuild. Use:

```bash
if [[ ! -v QWENTTS_DEVICE ]]; then QWENTTS_DEVICE=Vulkan0; fi
```

(`podman`'s `--env-file` passes `VAR=` through as set-and-empty, and `source` does the same, so both readers agree.) Pin it in a test: empty device ⇒ the flag is absent from argv.

## 6. Co-tenancy measurement (only after the tenant is live)

The gate is the **first tenant's** performance with a real request from the second in flight — not the second tenant's own speed. And price the tenant from a booted footprint, never from weights+KV+buffers: on an APU the compute buffers and any projector ride on GTT, which is host RAM; check `free` after the load, not before.