Monitoring and Tuning Your Server

Suggestions for Improving Processor Usage and Performance

If your data on processor performance indicates that processor queues are developing regularly or while a server is handling large numbers of connections, start by monitoring the server’s memory. Rule out a memory bottleneck or add more memory before (or in addition to) adding or upgrading processors.

In addition to the suggestions for optimizing thread values mentioned earlier in the section, consider doing the following:

Upgrade the L2 Cache When adding or upgrading processors, choose processors with a large secondary (L2) cache. File server applications, such as IIS, benefit from a large processor cache because their instruction paths involve many different components. A large processor cache (2 MB or more if external, up to the maximum available if on the CPU chip) is recommended to improve performance on active servers running IIS 5.0.
Improve DPC Handling Deferred Procedure Calls (DPCs) are similar to interrupts except that they have a lower Interrupt Request Level (IRQL). Unlike interrupts, DPCs can be delayed, allowing the processor to complete higher priority work. Platforms that distribute interrupts to all processors do not benefit from the Windows 2000 Server default DPC affinity. If you are administering a multiprocessor computer that distributes interrupts symmetrically, such as an Intel Pentium or Pentium Pro (P6) system for Windows 2000 Server, set the value of the ProcessorAffinityMask entry in the registry to zero. DPCs will be handled by the same processor that handled the interrupt from which the DPC evolved.
Caution Do not use a registry editor to edit the registry directly unless you have no alternative. The registry editors bypass the standard safeguards provided by administrative tools. These safeguards prevent you from entering conflicting settings or settings that are likely to degrade performance or damage your system. Editing the registry directly can have serious, unexpected consequences that can prevent the system from starting and require that you reinstall Windows 2000. To configure or customize Windows 2000, use the programs in Control Panel or Microsoft Management Console (MMC) whenever possible.
Add Network Adapters If you are administering a multiprocessor system that does not distribute interrupts symmetrically, you can improve the distribution of the processor workload by adding network adapters so that there is one adapter for every processor. Generally, you only add adapters when you need to improve the throughput of your system. Network adapters, like any additional hardware, have some intrinsic overhead. However, if one of the processors is nearly always active (that is, if Processor\ % Processor Time = 100) and more than half of its time is spent servicing DPCs (if Processor\ % DPC Time > 50), then adding an adapter is likely to improve system performance, as long as the available network bandwidth is not already saturated.
Upgrade Network Cards If you are adding or upgrading network adapters, choose those with drivers that support interrupt moderation. Interrupt moderation prevents the processor from being overwhelmed by bursts of interrupts. Consult the driver manufacturer for details. Also, if at all possible, use adapters that support TCP checksum offloading.
Limit Connections If you cannot upgrade or add processors, consider reducing the maximum number of connections that each IIS 5.0 service accepts. Limiting connections can result in connections being blocked or rejected, but it helps ensure that accepted connections are processed promptly.
Redesign the Web Site You can improve performance and reduce the processor workload by optimizing database use, optimizing the design of ASP pages, calling compiled components from scripts in ASP pages, using ISAPI instead of ASP (and ASP or ISAPI instead of CGI applications), substituting static Web pages for dynamic pages, eliminating the use of SSL except where it is necessary, moving trusted out-of-process applications into the Inetinfo process, and eliminating large bitmapped images or optimizing them to reduce their size. (For more information about optimizing scripts in ASP pages, see ASP Best Practices in this book.) It is also advisable to set long expirations on infrequently modified static files.
Adjust the Maximum Number of Threads IIS 5.0 tunes the number of threads in its process dynamically. The dynamic values are usually optimal. In extreme cases of very active or underused processors, however, it may help to adjust the maximum number of threads in the Inetinfo process. If you change the maximum number of threads, continue careful testing to make sure that the change has improved performance. The difference is usually quite subtle.