userspace-resource-manager-extensions

11. App Classification and Post Processing Blocks

Post Processing Blocks allow writing custom logic which will be hooked into when a certain process starts. More precisely, URM listens to proc events using a Netlink socket, when an event of the type: PROC_EVENT_EXEC is received, URM checks if a post processing callback has been registered for that particular process, if it has been, it gets executed.

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Registered Post-Processing Callbacks

Process Name	Callback	Source File
gst-launch-1.0	WorkloadPostprocessCallback	CamPostProcessing.cpp
gst-camera-per-port-example	WorkloadPostprocessCallback	CamPostProcessing.cpp
genie-t2t-run	workloadPostprocessCallback	GenieT2T.cpp

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Camera / GStreamer Post-Processing (CamPostProcessing.cpp)

WorkloadPostprocessCallback is triggered for gst-launch-1.0 and gst-camera-per-port-example.

Detection Flow

1. Read /proc/<pid>/cmdline and sanitize null bytes to spaces.

2. Scan the command line for GStreamer element identifiers:

   Encoder elements (checked first):

   • v4l2h264enc — hardware H.264 encoder
   • qtic2venc — Qualcomm C2 encoder

   Decoder elements:

   • v4l2h264dec — hardware H.264 decoder
   • qtic2vdec — Qualcomm C2 decoder

   Preview source:

   • qtiqmmfsrc — Qualcomm multimedia source
3. Extract extra attributes from the command line:
   • FPS: highest framerate=N[/D] value found (integer division)
   • Height: highest height=N value found
   • Width: highest width=N value found

4. Classify the workload and set SigId + SigType:

   Detected	SigId	SigType	Logic
   Single encoder	URM_SIG_CAMERA_ENCODE	0	exactly 1 encoder element
   Multi-stream encode	URM_SIG_CAMERA_ENCODE_MULTI_STREAMS	0 or 13	>1 encoder; SigType=0 if ≤12, 13 if >12
   Decoder	URM_SIG_VIDEO_DECODE	0, 5, or 21	thread count: <5→0, 5–20→5, >20→21
   Preview	URM_SIG_CAMERA_PREVIEW	0	qtiqmmfsrc present, no encoder/decoder

5. Call acquireSignal(sigId, sigType, pid, pid, SIGNAL_EXTRA_ATTRS_COUNT, extraArgs) directly and store the handle in cbData->mHandleAcq.

Decoder Thread Counting

For decoder workloads, the callback counts threads under /proc/<pid>/task/ whose /comm file contains the decoder element name (case-insensitive substring match). This count drives the SigType selection.

Encoder Count

For encoder workloads, the callback counts occurrences of the matched encoder string in the full cmdline buffer. More than one occurrence indicates a multi-stream pipeline.

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Genie T2T Post-Processing (GenieT2T.cpp)

workloadPostprocessCallback is triggered for genie-t2t-run.

The callback unconditionally sets:

• cbData->mSigId = CONSTRUCT_SIG_CODE(0xf1, 0x0123) → GENIE_T2T_RUN
• cbData->mSigType = DEFAULT_SIGNAL_TYPE

This routes the process to the GENIE_T2T_RUN signal, which affinizes IRQs to cores 0–5 and applies CPU affinity for inference threads.

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Writing a PostProcessing Callback

Let’s say we need to write a simple post-processing callback for the process: “gst-launch-1.0”, so that whenever a process with that command name is launched the callback is triggered.

static void workloadPostprocessCallback(void* context) {
    if(context == nullptr) {
        return;
    }

    PostProcessCBData* cbData = static_cast<PostProcessCBData*>(context);
    if(cbData == nullptr) {
        return;
    }

    // Main selection logic
    // Get the sigId and sigType for the signal which needs to be configured.
    // ........

    // Relay the information back to URM
    cbData->mSigId = sigId;
    cbData->mSigType = sigType;
}

__attribute__((constructor))
static void registerWithUrm() {
    // Post Processing Callback for process: "gst-launch-1.0"
    URM_REGISTER_POST_PROCESS_CB("gst-launch-1.0", workloadPostprocessCallback)
}

For callbacks that need to pass extra attributes (FPS, resolution) or call acquireSignal() directly, see the advanced pattern in 06-extension-api-guide.md.

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