DPC latency, explained in 3 minutes
What Deferred Procedure Calls are, why they can cause audio crackle and input hitches, and what a DPC number does — and does not — tell you.
The 3-minute version
When hardware needs the CPU’s attention, it fires an interrupt. Windows handles the urgent half immediately and defers the rest into a queue — those deferred chunks are DPCs (Deferred Procedure Calls). They run at high priority, above almost everything you do.
If a driver’s DPC routine takes too long or fires too often, everything else — audio buffers, input processing, frame delivery — waits. That’s why the symptoms of bad DPC behavior are audio crackle, mouse hitches, and micro-stutter that no average-FPS chart will ever show.
What the numbers mean
DPC latency tools report how long deferred routines occupy the CPU:
- Typical healthy systems spend the overwhelming majority of DPC time well under the audio buffer threshold — short, rare spikes are normal and inaudible.
- A problem looks like one specific driver (commonly network, storage or GPU) repeatedly holding execution long enough to starve time-sensitive work.
Two things a DPC number is not:
- Not an FPS predictor. You can have pristine DPC behavior and a GPU-bound 45 fps, or ugly DPC spikes on a system that benchmarks beautifully on averages.
- Not a score to minimize for its own sake. Chasing single-digit “lowest ever” readings has no audible or visible effect. What matters is whether spikes are long and frequent enough to disrupt real-time workloads.
How it’s treated in the Alchemy protocol
Responsiveness-window measurements related to interrupt/DPC behavior are advisory metrics in our reports: useful context and a good pointer for diagnosis, but they never drive a final verdict on their own — they’re proxies, and proxies don’t get to make claims.
When to suspect DPC problems
- Audio crackle or dropouts that correlate with network/disk activity
- Input feels momentarily “glued” while the system is otherwise idle
- Stutter that persists across GPU driver reinstalls and in-game settings changes
If that sounds familiar, a diagnosis-first Performance Audit is the honest way in: we measure, we identify the offending driver if there is one, and the Baseline Report tells you what’s actually going on — before anything is changed.