Analyzing Processor Activity

Monitoring Interrupts

Sharply rising counts for interrupts can affect your processor's performance, and you should investigate their cause. The Processor\Interrupts/sec counter reports the number of interrupts the processor is servicing from applications or hardware devices. You should expect interrupts to range upward from 1,000 per second for computers running Windows 2000 Server and upward from 100 per second for computers running Windows 2000 Professional. This interrupt rate is dependent on the rate of disk I/O operations per second and network packets per second. If your interrupt counter values are out of range, there might be hardware problems such as a conflict between the hard-disk controller and a network adapter. You can use System Information and Device Manager in the Computer Management console to check for problems with the disk controller or network adapter.

You might want to monitor interrupts along with I/O activity involving both disks and network cards. Use the Disk Reads/sec or Disk Writes/sec counters on the PhysicalDisk object to monitor disk I/O as described in "Examining and Tuning Disk Performance" in this book. Use the network transmission counters to monitor network activity as described in "Monitoring Network Performance" in this book. You can tell if interrupt activity is becoming a problem by determining the ratio of interrupts to I/O operations. An optimal ratio is one interrupt to four or five I/O operations. A one-to-one correspondence between these factors indicates poor performance and requires action.

If network or disk I/O is involved, you should consider upgrading to a controller and a driver that support interrupt moderation or interrupt avoidance. Interrupt moderation allows a processor to process interrupts more efficiently by grouping several interrupts to a single hardware interrupt. Interrupt avoidance allows a processor to continue processing interrupts without new interrupts being queued until all pending interrupts are complete. For more information about managing interrupts from network adapters, see "Monitoring Network Performance" in this book.

High values for % Processor Time for threads of the System process can also indicate a problem with a device driver.