When a game stutters even though your FPS looks healthy, the culprit is often a driver hogging the CPU for too long and blocking real-time work — the same problem that causes audio dropouts. LatencyMon is a free tool that measures DPC and ISR execution times and names the exact driver responsible. This guide shows how to read its output and turn a vague “my PC hitches” into a specific fix.
What LatencyMon actually measures
Deferred Procedure Calls (DPCs) and Interrupt Service Routines (ISRs) are how Windows handles hardware events. If one driver’s DPC runs for, say, 2000 microseconds instead of a healthy sub-100, everything else waits, producing a micro-stutter or an audio pop. LatencyMon watches these in real time and flags whether your system can handle real-time audio and, by extension, smooth gaming.
Reading the numbers
| Metric | Healthy | Problem range |
|---|---|---|
| Highest DPC (µs) | Under ~500 | Over 1000 sustained |
| Highest ISR (µs) | Under ~250 | Over 500 |
| Highest reported latency | Under ~1000 µs | Several thousand µs |
Running a proper test
Close background apps, launch LatencyMon, and press the green Play button. Let it run for at least 5-10 minutes while you use the PC normally — browse, alt-tab, and if possible run your game windowed. The “Drivers” tab then sorts by highest execution time. The top offender’s file name is your lead: nvlddmkm.sys points to the NVIDIA GPU driver, ndis.sys or a Wi-Fi driver points to networking, Wdf01000.sys is often a chained driver rather than the true source.
Common offenders and fixes
Network adapters are the most frequent cause: disable Wi-Fi if you are wired, update the LAN/Wi-Fi driver, and turn off “Interrupt Moderation” tweaks only if needed. Storage controllers acting up usually mean an outdated chipset or SATA driver. GPU spikes often trace to an unstable overclock or a driver that needs a clean DDU reinstall. USB spikes can come from a flaky hub or a problematic peripheral — unplug devices one at a time to isolate.
From diagnosis to cure
Work one variable at a time: update or roll back the flagged driver, re-test, and compare the highest DPC value. A fix should drop that number by an order of magnitude. If disabling a device makes the spikes vanish, you have found your culprit even if a firmware or driver update is still pending from the vendor.
Isolate the culprit methodically
Once LatencyMon names a top offender, resist changing five things at once. Disable or update that single driver or device, re-run the test for the same duration, and compare the highest DPC value directly. A genuine fix usually drops the number dramatically — from thousands of microseconds back under a few hundred. If it barely moves, you have the wrong suspect and should look at the next driver in the list.
A practical elimination order
Start with networking (disable Wi-Fi if wired), then GPU driver, then storage/chipset, then USB peripherals unplugged one at a time. Wireless adapters and their power-management settings are the single most common cause, so in Device Manager open the adapter’s power management tab and disable “Allow the computer to turn off this device to save power.” That one change resolves a surprising share of periodic stutter and audio dropouts on laptops and desktops alike.
Keep your baseline numbers written down. Diagnosing latency is all about before-and-after comparison, and a saved record of your highest DPC per driver makes it obvious whether a driver update helped or quietly made things worse.
FAQ
My highest latency is huge but games feel fine — do I care?
Only if you actually experience stutter or audio dropouts. A single brief spike during startup is normal. Sustained high DPC times that coincide with hitching are the ones worth chasing.
Does LatencyMon fix anything itself?
No — it only diagnoses. It points you to the offending driver or device; you apply the fix (driver update, rollback, disabling a device, or resolving an unstable overclock).
Bottom line: LatencyMon converts mystery stutter into a named driver. Run it for several minutes, read the highest DPC and the top driver file, then update, roll back, or disable that component and re-measure. It is the fastest path from “something hitches” to a concrete fix.
