APIC – Advance Real-time optimization best practice

Keep branch predictability high; prefer straight-line code in the critical path.

Lockless handoff patterns

Use SPSC ring buffers or double-buffer swaps to transfer frame-sized data to background threads.

// Producer (real-time): write full frame descriptor
if ((head+1) % SIZE != tail) { buffer[head] = desc; head = (head+1)%SIZE; }


// Consumer (background): read descriptors and serialize
if (tail != head) { desc = buffer[tail]; tail = (tail+1)%SIZE; }

Memory and cache

• Align hot structures to cache-line boundaries to avoid false sharing.
• Use contiguous arrays of POD structs for fast sequential access.
• Prefer object pools for frequently-created objects.

Multi-rate strategy

Keep the high-rate loop minimal. Offload heavy computation to sub-rate tasks and interpolate results when necessary.

// example: 1kHz main, 250Hz mid, 62.5Hz low
work_fast();
if ((frameId & 0x3) == 0) work_mid();
if ((frameId & 0xF) == 0) work_low();

Logging & telemetry

• Collect jitter histograms in-memory and flush summaries periodically.
• Record small descriptors in the hot path and let the consumer write large blobs.

// in-loop histogram (microseconds)
static uint64_t hist[1024] = {0};
uint64_t t = frameEndUs - frameStartUs;
size_t bin = (t < 1023) ? t : 1023;
__atomic_fetch_add(&hist[bin], 1, __ATOMIC_RELAXED);

Troubleshooting

• If you see frequent overruns: profile the loop, check IRQ affinity, and verify CPU frequency governor.
• Investigate kernel messages for unexpected interrupts or kernel threads stealing cycles.
• Reduce logging and move work to lower rates before changing hardware or the frame rate.

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