Determining and Tuning Priority

If a system has high rate of CPU utilization, it is generally best to add processing power by upgrading to a faster processor or to add a processor for symmetric multiprocessing (SMP). However, if you find that some threads are consistently unable to get processor time, you can adjust the thread's priority to allow them to run temporarily. Adjusting thread priority is not recommended as a long-term solution but is a useful illustration of the effect of thread priority on thread activity. Although this section covers elevating priority to allow a process to run, you can also lower the priority of a process if you want it to run in the background while nothing else is running.

Windows 2000 and the Windows 2000 Resource Kit companion CD include several utilities for monitoring the base priority of processes and threads and the dynamic priority of threads. They include:

• In Windows 2000: System Monitor and Task Manager.
• With Support Tools on the Windows 2000 operating system CD: Pviewer.

Warning

Changing priorities might destabilize the system. Increasing the priority of a process might prevent other processes, including system services, from running. Decreasing the priority of a process might prevent it from running, not merely force it to run less frequently. In addition, lowering priority does not necessarily reduce the amount of processor time a thread receives; this happens only if it is no longer the highest-priority thread.

System Monitor

System Monitor lets you watch and record—but not change—the base and dynamic priorities of threads and processes. System Monitor has priority counters on the Process and Thread objects:

• Process\Priority Base
• Thread\Priority Base
• Thread\Priority Current

Figure 7.18 is a chart of the base priorities of several processes. The Idle process (the white line at the bottom of the chart) runs at a priority of Idle (0), so it never interrupts another process.

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Figure 7.18 Processes and Their Base Priorities

Figure 7.19 is a chart of the dynamic priority of the single thread in the Paintbrush utility (Mspaint.exe) as it changes in response to user actions. The base priority of the thread is 8 (Foreground Normal). During this period of foreground use, the dynamic priority of the thread is 14, but drops to 8 when other processes need to run.

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