Some processor platforms can distribute interrupts across available processors; this capability is called symmetric interrupt distribution. These platforms typically include Pentium Pro and later processors; however, some Pentium processors also have this capability. Although symmetric interrupt distribution is designed as a way to balance interrupt activity, it can sometimes result in poor processor-cache performance. Partitioning interrupts to a specific processor is a strategy for addressing this problem. The Interrupt Filter tool on the Windows 2000 Resource Kit companion CD enables you to set the affinity for interrupts generated from disks or network adapters to a particular processor. This improves efficiency by taking advantage of cache locality, which can be lost when interrupts are serviced by any available processor. See Windows 2000 Professional Help for the Resource Kit tools for information about the requirements for using Interrupt Filter.

To help improve processor performance, some newer network adapter drivers provide an advanced feature known as interrupt moderation or interrupt avoidance. When the driver detects a high rate of interrupts from the network adapter, the interrupt-moderation code disables interrupts and accumulates the interrupts, sending them to the processor as a group of interrupts. Using a network adapter that supports interrupt moderation can provide better performance if your workload is network-intensive.

Bypassing I/O Counts

By default, Task Manager continuously measures data for process I/O operations that you can select and display under the Processes tab in Task Manager. In a multiprocessor environment, this data is shared by the processors on which the process runs. When a process that generates considerable disk and network I/O, such as a database service, runs on several processors, updating the shared measurements of process I/O and global I/O operations can slow the system. You can improve the performance of I/O-intensive operations on SMP systems if you configure the system to bypass the global I/O counters and Task Manager process I/O counters. To do so, add the CountOperations entry to the registry as a REG_DWORD in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\I/O System\. Set the entry value to 0. When so configured, Task Manager no longer provides per-process I/O measurements. For more information about Task Manager, see "Overview of Performance Monitoring" earlier in this book.

Hardware Interrupt Partitioning

Bypassing I/O Counts