Apu Memory Tuner

APU Memory Tuner

Help the user inspect and tune the shared-vs-dedicated memory split on AMD Ryzen APUs with unified memory architecture (UMA). The user states intent ("I want to run a 70B model", "I just want my games to be smooth"); this skill picks the numbers, explains the trade-offs, and applies the change where it can.

What's actually going on

On a UMA APU (Strix Halo, Strix Point, Krackan, Phoenix, Hawk Point, etc.) the CPU and integrated Radeon share one physical pool of DRAM. There is no separate VRAM chip. Two logical knobs cut that pool up:

| Knob | Where set | What it does | Reversible? | |---|---|---|---| | Dedicated VRAM (a.k.a. UMA Frame Buffer / carve-out / GART) | BIOS, requires reboot | Permanently reserves DRAM for the GPU. CPU can't see it. | Only via BIOS. | | Shared GPU memory (a.k.a. GTT) | Kernel/driver-managed | Dynamic, OS-reclaimable cap on how much system RAM the GPU may map at a time. | Yes; Linux: amd-ttm. Windows: no user knob. |

Key insight the rest of this skill rests on: "VRAM" and shared RAM run at the same speed on UMA, because they're the same DRAM. So the right default for AI workloads is small VRAM + large GTT, not the other way around.

When to use

Use this skill when the user wants to:

• Run a model that doesn't fit ("out of VRAM", "GPU OOM" on an iGPU).
• Inspect the current memory split before changing anything.
• Move the slider toward more shared memory (LLMs, large image gen) or

toward more dedicated VRAM (gaming, predictable framebuffer).

• Revert any prior changes.

Do not use it for: discrete Radeon cards (no GTT/UMA on those), Apple Silicon (different architecture entirely), or NVIDIA/Intel GPUs.

Prerequisites

State these to the user up front so a missing one doesn't surface as a mystery script error halfway through:

• GPU architecture: AMD APU with integrated Radeon. Officially tuned

for RDNA3.5 (gfx1150 / gfx1151 / gfx1152); RDNA3 / RDNA2 APUs work but with conservative profile numbers.

• OS: Linux (kernel + amd-ttm path) or Windows (guided BIOS path).

macOS is not supported.

• Linux kernel: see the live AMD matrix linked from reference.md.

The detection script enforces a conservative floor (mainline 6.18.4 / Ubuntu HWE 6.17.0 / Ubuntu OEM 6.14.0).

• Linux extras: pipx install amd-debug-tools for the amd-ttm CLI.

The skill prints this command but never installs it silently. Reading the BIOS carve-out from dmesg typically requires sudo.

• Windows extras: AMD Adrenalin Software 25.x or newer if the user

wants the Variable Graphics Memory slider as an alternative to BIOS.

• Reboot tolerance: any tuning change requires a reboot. Don't propose

this skill mid-workload.

Silent footguns to surface when relevant:

• HSA_OVERRIDE_GFX_VERSION — users running ROCm/PyTorch on an APU often

set this to convince ROCm the iGPU is a supported target. It does not affect memory tuning, but if the user reports HIP error: invalid device after raising GTT, this env var is usually the cause, not the GTT change.

• Windows Win32_VideoController.AdapterRAM is a 32-bit field capped at

4 GiB. If the user's reported "dedicated VRAM" is exactly 4096 MB, that's the WDDM truncation, not the real BIOS reservation. The real value lives in Task Manager > Performance > GPU.

The four-step flow

Run these in order. Each one is read-only until step 4.

[ ] 1. Detect platform and support level
[ ] 2. Show current configuration
[ ] 3. Pick a profile from the user's intent
[ ] 4. Apply (Linux) or print BIOS guidance (Windows); verify after reboot

Step 1: detect platform

python scripts/detect_platform.py

Add --json for parseable output. Exit codes:

| Exit | Meaning | Next action | |---|---|---| | 0 | Supported AMD APU. | Continue to Step 2. | | 2 | Wrong hardware (not an AMD APU, or unclassifiable). | Stop. Tell the user this skill can't help them. | | 3 | AMD APU but a hard prerequisite is missing (Linux kernel too old). | Stop. Tell the user the prereq and stop. Do not attempt to upgrade the kernel from this skill. |

The script reports the OS, CPU, GPU LLVM target (e.g. gfx1151), the generation bucket (RDNA3.5 / RDNA3 / RDNA2 / older), total RAM, and on Linux the kernel version vs. the minimums in the AMD doc.

Step 2: show current configuration

python scripts/show_config.py

Reports current dedicated VRAM, current shared-GPU cap, total RAM, and on Linux the raw pages_limit value plus a rocminfo sanity-check of what the runtime actually sees. Note any messages it prints — Linux often needs sudo for the dmesg read of the BIOS carve-out, and Windows' AdapterRAM field is capped at 4 GiB by WDDM (real value lives in Task Manager).

Step 3: pick a profile

Ask the user what they want, in workload terms, not numbers. Map their answer to one of these:

| Profile | What it does | Use when the user says... | |---|---|---| | large-models (default) | GTT to ~75% of RAM, BIOS VRAM at the floor (0.5 GB). | "Run a big model", "fit Llama 70B", "I keep getting OOM on the iGPU", "give the GPU as much memory as possible". | | balanced | GTT at the kernel default (~50%), 1 GB BIOS VRAM. | "I just do mixed dev work", "back to defaults", "don't waste RAM on the GPU". | | graphics | GTT at default; BIOS VRAM raised to the larger of 8 GB or 25% of RAM. | "I'm gaming", "I want a predictable framebuffer", "stuttering in games". | | reset | Revert all changes this skill made. | "Undo it", "go back to stock". | | custom | Use the explicit --gtt-gb / --vram-gb the user passed. | "I want exactly N GB". |

Default: if the user is here at all and didn't specify, they almost always want large-models -- that's the only profile that meaningfully changes the experience for the workload that brought them here (running a model that didn't fit). Use it unless they explicitly said gaming, said they want defaults, or said an exact number.

If you still can't tell, use the AskQuestion tool with the five options above labeled in plain English; do not invent a sixth.

Step 4: apply or guide

python scripts/apply_profile.py --profile 

Add --dry-run first if the user wants to see the planned change before committing.

What happens on each OS:

• Linux: writes the new GTT cap via amd-ttm --set (which persists

to /etc/modprobe.d/ttm.conf). Reboot is required; the script tells the user but never reboots automatically. If amd-ttm is missing, the script exits with a clear install hint (pipx install amd-debug-tools) — do not install it yourself without confirming with the user.

• Windows: prints step-by-step BIOS instructions for the UMA Frame

Buffer Size, plus a note about AMD Adrenalin's "Variable Graphics Memory" slider as an alternative on supported laptops. Nothing is written to disk or registry. The script never modifies BIOS for the user.

Then re-run python scripts/show_config.py after reboot to verify.

OS-specific reality check

| Capability | Linux | Windows | |---|---|---| | Inspect dedicated VRAM | Yes (dmesg/journalctl, may need sudo) | Yes (Task Manager / dxdiag; AdapterRAM is truncated) | | Inspect shared cap | Yes (/sys/module/ttm/parameters/pages_limit) | Yes (dxdiag "Shared Memory") | | Change shared cap automatically | Yes (amd-ttm) | No — WDDM-managed, not user-tunable | | Change dedicated VRAM automatically | No (BIOS only) | No (BIOS only; VGM via Adrenalin is the closest UI) |

Net effect: on Windows, raising the BIOS UMA Frame Buffer Size is the only real way to give the GPU more memory. On Linux you almost always want to lower BIOS VRAM and raise GTT instead.

Safety rules

• Never auto-reboot. Always tell the user the reboot is needed and let them

do it.

• Never touch BIOS programmatically. The script prints instructions; the

user navigates the firmware menu.

• Never silently install amd-debug-tools. Print the pipx install line

and ask before running it.

• Never set a profile whose validation fails. The script refuses GTT

targets above 95% of RAM or VRAM targets above 50% of RAM.

• Never claim a change took effect before the user has rebooted and

re-verified with show_config.py.

Verification checklist

Mark this skill complete only when all are true:

• [ ] python scripts/detect_platform.py exits 0.
• [ ] python scripts/show_config.py reports the new values after the

reboot following Step 4.

• [ ] The user has tried the workload that motivated the change (loaded

the model, launched the game) and confirmed the new headroom helps.

• [ ] On Linux, cat /sys/module/ttm/parameters/pages_limit matches what

apply_profile.py reported.

If any box is unchecked the change either didn't take effect or the user hasn't validated it yet — say so out loud rather than declaring success.

Reference

For the full glossary, the link to AMD's authoritative kernel-version / ROCm-compatibility matrix, per-OEM BIOS notes, profile math, and troubleshooting, see [reference.md](reference.md).

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: amd
• Source: amd/skills
• License: MIT
• Homepage: https://developer.amd.com/

Install and usage instructions live in the source repository linked above.