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# Graphics Execution
> **Scope.** How the emulated vGPU runs **3D graphics** work — the OpenGL and
> Vulkan command streams a stock guest submits — on the physical GPU, and what
> is proven about it. This is the shared machinery behind
> [`OpenGL.md`](OpenGL.md), [`Vulkan.md`](Vulkan.md) and the Windows/DirectX
> target ([`DirectX.md`](DirectX.md)); CUDA compute uses the same submission and
> completion path for a different engine workload
> ([`Execution-Frontier.md`](Execution-Frontier.md)). Canonical sources:
> [`../docs/04-implementation/05-graphics-execution-plan.md`](../docs/04-implementation/05-graphics-execution-plan.md)
> (the plan and milestone ladder) and
> [`../docs/04-implementation/04-real-render-walls.md`](../docs/04-implementation/04-real-render-walls.md)
> (the measured walls); the docs tree wins on disagreement.
Status: 2026-11-09, tree `master @ 4acc81e8`. Tags: `[live]` observed end to
end; `[wip]` partially built; `[wall]` current blocker; `[target]` defined
success state; `[planned]` designed, not built.
## 1. What "real pixels" means
The acceptance target is strict: a **stock** guest GL or Vulkan application's
draw commands are executed by the physical GPU's fixed-function 3D pipeline
(vertex fetch, primitive assembly, rasterisation, fragment work, ROP), the
render target is readable by the guest, and that image reaches the capture
path through the emulated mdev. The pixels must not come from another GPU, a
software rasteriser, or a host display round-trip.
(The project has also published two deliberately-labelled two-VM demo videos
that use the standard `virtio-gpu`/`virgl` virtual GPU on a host integrated
GPU, and a CUDA-animation video that *does* run on the emulated vGPU through
the compute path. The `virgl` videos are honest demonstrations of the guest
experience; they are not this execution path, and their captions say so.)
## 2. The path a graphics command takes
```mermaid
graph TD
APP["Guest applications<br/>OpenGL · Vulkan · CUDA"] --> LIB["Guest user space<br/>GL: GLX client + the driver's GL core<br/>Vulkan: the NVIDIA ICD<br/>CUDA: libcuda"]
APP --> X["X server (Linux GL)<br/>GLX module + the NVIDIA DDX"]
LIB --> KMD["Guest kernel: nvidia.ko<br/>RM core, GSP client, channels, modeset/drm"]
X --> KMD
KMD -- "GPFIFO rings + doorbell;<br/>method streams in push buffers" --> VG["Host module vgsp.ko<br/>device model + emulation core"]
VG --> L1["Lane 1: verbatim 3D<br/>method-stream replay"]
VG --> L2["Lane 2: synthesized launch<br/>from a captured section"]
VG --> L3["Lane 3: forwarded CUDA<br/>launch (compute)"]
L1 --> FE["Physical GPU<br/>front-end fetch -> GR engine"]
L2 --> FE
L3 --> FE
FE -- "engine-authored releases<br/>(semaphores in guest memory)" --> VG
VG -- "completion relay: MSI-X +<br/>poller/event wake the guest" --> KMD
```
```text
guest apps (GL / Vulkan / CUDA)
-> guest user space (GLX client + GL core, Vulkan ICD, libcuda)
-> guest X server (GLX module + NVIDIA DDX) [OpenGL]
-> nvidia.ko: channels, GPFIFO rings, doorbells [all APIs]
-> vgsp.ko: capture sections, decode pushes, forward
-> physical GPU front-end -> GR engine (3D + compute) / copy engines
<- engine-authored releases written into guest memory
<- completion relay (MSI-X + wakes) back to the guest
ASCII fallback above; the diagram shows the three execution lanes.
```
## 3. The three execution lanes
Graphics work reaches the engines today in one of three shapes, in increasing
fidelity:
1. **Verbatim 3D method-stream replay** `[live]`. The emulation captures the
X server's graphics-class (`0xC597`, `TURING_A`) section from its channel,
relocates the operand addresses into host-built shadow pages the engine can
reach, and submits the stream unchanged. The engine retires it: the uploads
(`LINE_LENGTH_IN`/`LAUNCH_DMA`), the state, program and texture binds, and
the release all execute with no MMU fault. This proves the *mechanics* of
3D execution — object bind, window placement, operand relocation,
completion — on real hardware.
2. **Synthesized launch from a captured section** `[live]`. A compute-shaped
launch built from the captured section (operand list, program, a 64-word
launch descriptor) reaches the engine and retires real `sm_75` SASS; the
Turing shader-program-header form (`V3`) is accepted with zero header
faults across repeated launches. This proved engine-side dispatch before
the verbatim lane existed. The program itself is still a development
stand-in at this rung — execution proof, not pixels.
3. **Forwarding the client's own pushes** `[wip]`. The GL client's own
channels now register, submit and retire: the direct-GL GR channel
(`0xbeef0100`) and its CE siblings (`0xbeef0101`/`0xbeef0102`) are
discovered, their rings and releases are decoded, and the X server's DDX
kick channel (`0xbfef0002`) is decoded from its ring head with its
class-2D notification authored. What remains is completing the GLX
context-creation handshake and the client's kick-slot wait (§6), not
making the pushes readable.
## 4. The channel and object picture
* **Every submission lives on a channel**: a GPFIFO ring plus engine objects,
with a USERD the driver advances its put pointer in and a doorbell the host
module traps. Channels are typed by engine: a graphics channel carries 3D
state and draws; copy-class channels carry memory movements.
* **The graphics object class** the guest's 3D stream binds is the Turing
graphics class, `0xC597`. Streams now come from both the **X server's
channel** and the **direct GL client's own channels** (`0xbeef0100` GR plus
the `0xbeef0101`/`0xbeef0102` CE siblings); the 2D present/readback work
rides lighter 2D-class and copy-engine shapes.
* **Display and modeset** `[live]`. The guest's modeset path is served by an
emulated display engine: the display push-buffer channels (core `0xc57d`,
window `0xc57e`, immediate/window `0xc57b`) are registered, their push
buffers parsed, and the notifier/`UPDATE` completion authored. This is what
lets nvidia-modeset/NvKms register (`/dev/dri`), X settle and GLX clients
obtain a real GL context. The display-capability seam is parameterised in
the campaign configuration.
* **Cells of state**: 3D streams are long—hundreds of method words per draw —
and mix state binds (viewport, render target, ZS, blend/ROP), program and
constant binds, vertex/index streams and draw-issuing methods. The capture
machinery recognises the init-shaped operands today; the per-draw state
vocabulary is being extended ([G-B in the plan](
../docs/04-implementation/05-graphics-execution-plan.md)).
* **Synchronisation**: tracking semaphores, notifications and fence values
written by the engine; the guest's swap/present waits sit on top of those.
## 5. Completion, fences and presents
The acceptance signal is the **engine-authored release**: a semaphore the
engine writes when the work completes. For GL, completion flows through the
channel's semaphores/notifications to the X server and the app's swap wait;
for Vulkan, the client's fence value is released; for CUDA, the launch's
release group wakes the client. The emulation relays engine completions into
guest-observable memory (MSI-X plus a poller), and the guest resumes from
there.
For the display path, completion is the notifier write and `UPDATE ->
FINISHED`; a completion event deferred by the reply path is force-retried
until it posts, so the X server's mode set finishes.
During bring-up the module also carries a **diagnostics-only mirror** for apps
that spin on a shared progress word; it exists so a run can proceed while the
natural completion path is being finished. The 60-fps milestone explicitly
requires it switched off, along with any external poke.
## 6. Where the frontier is (ranked walls)
1. **The X GLX context-creation completion** `[wall]`. With the UVM
channel-pool and direct-GL submission walls closed, the X server spins in
its RM ioctl path (`_nv018351rm`) while a GL client's GLX context request
waits on the X reply. The X DDX's own channels and the GLX reply are the
current named objects. (Fullscreen GZDoom's client-triggered mode set can
still wedge X; the campaign path is a settled X plus windowed GZDoom.)
2. **The client kick-slot word** `[wall]`. The GL client polls a kick-slot GPU
address for its completion; the RM notifier page is a different object, so
the completion must be authored at the client's kick-slot address.
3. **Non-black frames** `[wall]`. Once the GLX context completes and the
client's kick wait resolves, the capture must show motion; every frame
captured so far is black.
4. **Sustained frame rate, and two VMs** `[target]`. The defined end state:
60 fps in one VM with no forcing, then two VMs on two mediated devices
with non-black frames in both.
## 7. What is proven today
| Capability | State |
|---|---|
| X server initialises on the emulated vGPU (driver DMA sanity push, ScreenInit) | `[live]` |
| Display engine serves the modeset push buffers; notifier plus `UPDATE -> FINISHED` | `[live]` (campaign configuration) |
| nvidia-modeset/NvKms registers (`/dev/dri/card0`, `renderD128`, `fb0`); `nvidia-smi -L` enumerates | `[live]` |
| `glxinfo` reports the emulated GPU with the NVIDIA renderer (OpenGL 4.6.0, direct rendering) | `[live]` |
| GZDoom obtains a real GL context; windowed reaches renderer startup | `[live]` (pixels frontier) |
| GL section capture: the X server's `0xC597` stream decoded | `[live]` |
| Verbatim 3D method-stream replay retired by the engine (no MMU fault) | `[live]` |
| Synthesized launch executes real `sm_75` SASS; Turing `V3` program header accepted | `[live]` |
| 2D screen fills and copy-engine present ops execute | `[live]` |
| Direct GL client: device-init gate handled, channels allocate, readback path returns clean | `[live]` |
| Direct GL client channels submit and retire (GR `0xbeef0100`, CE `0xbeef0101`/`0xbeef0102`); DDX kick channel decoded | `[live]` |
| X GLX context-creation completion and the client kick-slot word | `[wall]` |
| Non-black pixels from the emulated vGPU's 3D pipeline | `[wall]` |
| Windows/DirectX guests | `[planned]` |
## 8. What is not claimed
* No non-black pixel has been produced by the emulated vGPU's 3D pipeline yet.
* Display/KMS bring-up (NvKms, `/dev/dri`, X, a real GL context) is not a
rendered-frame claim; the GLX context-creation and kick-slot completions are
the current walls.
* No frame-rate or latency numbers: the scheduled measurement is defined
(60 fps over 60 s, no forcing) but not yet met.
* The `virgl`-based demo videos are a different, labelled path — not this one.
## 9. Related pages
* [`OpenGL.md`](OpenGL.md) — the guest OpenGL path and its status.
* [`Vulkan.md`](Vulkan.md) — the guest Vulkan path and its status.
* [`DirectX.md`](DirectX.md) — Windows guests and the DirectX target.
* [`Execution-Frontier.md`](Execution-Frontier.md) — the CUDA compute chain,
proven end to end.
* [`Physical-GPU-Backend.md`](Physical-GPU-Backend.md) — the backend the work
is forwarded to.
* [`Introduction-to-GMMU.md`](Introduction-to-GMMU.md) — channels, GPFIFO,
engines, and page tables.
* [`Host-Module.md`](Host-Module.md) — where capture, decode and forwarding
live.
* [`../docs/04-implementation/05-graphics-execution-plan.md`](../docs/04-implementation/05-graphics-execution-plan.md) —
the canonical plan: gap list, three approaches, and the M-GL1..M-GL6
milestone ladder with gates.
|
