Task Manager for gamers: what is using your PC while you play

The game hitches, you press Ctrl+Shift+Esc, and the table is already moving: the game's CPU figure looks modest, the GPU column is nowhere near 100, System interrupts sits near the top, and a browser has a small leaf next to it. Each reading measures something specific, and misreading one sends you after the wrong fix.

Open it and pick the page

Press Ctrl+Shift+Esc, or right-click Start and select Task Manager. If it opens as a short list, select More details. Two pages answer "what is running":

Processes, which Microsoft's Task Manager troubleshooting article describes as a "list of apps and background processes, and the resource usage of each". Rows are grouped under Apps, Background processes and Windows processes, and a program's child processes fold under one expandable row.
Details: every process on its own row, "regardless of whether they're apps or background processes", with more data per process. Priority is set here.

On the Details page, right-click a column heading and choose Select columns to add what you need.

The CPU column is a share of the whole processor

The CPU figure is a percentage of all logical processors together. Microsoft's example uses eight of them: "if a process uses 12.5 percent of the CPU capacity, the process is using the equivalent of one full CPU." So a game showing 12.5% on such a machine can have a thread with no time to spare, and the total will not tell you.

To see it, open Performance > CPU, right-click the graph and choose Change graph to > Logical processors; the graph splits into one per logical processor. Show kernel times in the same menu splits the trace into two colours, kernel and user. If one processor sits near its ceiling while the graphics card is not busy, GPU not at 100% explains how to read that.

The GPU column is the busiest engine

A GPU is made of engines that can run in parallel, and the column has to pick one figure. The DirectX team's post on GPUs in Task Manager explains the choice: it shows "the utilization of the busiest engine, across all GPUs, for that process". The GPU engine column names which GPU and which engine that figure belongs to, such as 3D, Copy, Video Decode or Video Encode. On a PC with two GPUs it is the quick check of which one a game landed on; which GPU a game runs on covers changing it.

Performance > GPU shows two kinds of memory. Dedicated GPU memory is "exclusively reserved for use by the GPU"; shared GPU memory is "normal system memory that can be used by either the GPU or the CPU". The Details page can show both per process through Select columns, and running out of VRAM is the page for reading them during a game. Next to a dedicated graphics card, the Performance page also shows its temperature in Celsius; Microsoft's 2019 announcement of the feature said it needs a driver that supports WDDM 2.4 or later.

Startup apps: impact is measured at startup

The Startup apps page, also at Settings > Apps > Startup, lists what starts with Windows. Its Startup impact column measures startup, per Microsoft's startup apps page: Low is under 300 milliseconds of CPU and under 292 kilobytes of disk, High is more than 1 second of CPU or more than 3 megabytes of disk. A High rating tells you what an app costs while Windows starts, not what it does once a game is running. For that, find it on the Processes page while you play.

The leaf is Efficiency mode

When the Windows performance team introduced Efficiency mode, it described two changes: it "reduces process base priority to low" and "sets QoS mode to EcoQoS", and EcoQoS "could mean running the processor at a lower frequency to save power". A process in that mode shows Efficiency mode in the Status column and a leaf icon. A greyed-out option means "a core Windows process, and throttling that process may affect the system". The same post said Edge and Chrome were experimenting with lowering their own base priority and using power-efficiency APIs, which Task Manager also shows as Efficiency mode, so a leaf you never set is not a fault.

It is meant for background work. Applied to the game, it lowers the game's own priority.

System interrupts is not a program

Task Manager describes this row as "Deferred procedure calls and interrupt service routines": time the processor spends in drivers' interrupt code rather than in any app. An archived Microsoft blog post called these routines "the silent killers of system performance": they are "the highest priority code that runs in the system", and when they run too long or too often they "can cause audio and video glitches, mouse freezes". A high or spiking figure here points at drivers, and DPC latency: when a driver is what stutters shows how to find which one.

Priority: what Set priority changes, and for how long

On the Details page, right-click a process and choose Set priority: Realtime, High, Above normal, Normal, Below normal or Low; the Base priority column shows the current one. Priority decides who runs first when threads compete for a processor: in Microsoft's scheduling documentation, a higher-priority thread that becomes ready stops a lower-priority one. The same page says "By default, the priority class of a process is NORMAL_PRIORITY_CLASS", chosen when the process is created. So a change made in Task Manager lasts until the game closes; the next launch starts at Normal again unless whatever starts the game sets or passes on another class.

Three cautions:

The same documentation says "You should almost never use REALTIME_PRIORITY_CLASS, because this interrupts system threads that manage mouse input, keyboard input, and background disk flushing." Task Manager may also answer "Unable to set priority to Realtime. The priority was set to High instead."
High has its own warning: "a high-priority class application can use nearly all available CPU time".
Some processes refuse any change ("Unable to change priority"). Protected processes, for one, do not hand out the access right a priority change needs.

If a game keeps coming up at a priority you never chose, the game itself, its launcher or a persistent rule is setting it at every start. w0a's Game and app priorities card removes standing High-priority rules, and the I/O priority stored with them, whichever tool wrote them: on the Fix page, search oncelik and press the button on the card (Game and app priorities).

Disk and network: Resource Monitor

Task Manager has an Open Resource Monitor command, and perfmon /res opens it directly. Its Disk tab lists Processes with Disk Activity and, under Disk Activity, each file being read or written with Read (B/sec), Write (B/sec) and Response Time (ms). Its Network tab lists Processes with Network Activity and TCP Connections. That ties a disk spike to one process and one file; Disk at 100% in Task Manager continues from there.

Ending a process

When Microsoft redesigned Task Manager for Windows 8, it described End task as acting at once, with no "Are you sure?" and no prompt to save. It also said apps "are generally safe to kill", while killing some Windows processes "can cause a blue screen". On the Details page, ending a process asks first, and the question warns: "If you end a system process, it might result in system instability." When a game still responds, save and close it from its own menu.

What does not help

Realtime for the game. It can interrupt the system threads that handle mouse and keyboard input, as the warning above says.
Ending Windows processes to free resources. Killing some of them can cause a blue screen.
Turning performance counters off. Some optimisation guides write a value, Disable Performance Counters, that switches them off. If Performance Monitor finds no counter sets at all, or a monitoring tool sees no data, w0a's Performance counters card deletes that value: on the Fix page, search performans and press the button on the card (Performance counters).

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