4    Improving System Performance

You may be able to improve Tru64 UNIX performance by tuning the operating system or performing other tasks. You may need to tune the system under the following circumstances:

• You are running a large or specialized configuration that requires you to modify the default values of some subsystem attributes.

• You want to optimize performance in a generally well-functioning system.

• You want to solve a specific performance problem.

To help you improve system performance, this chapter describes the following:

• Steps for configuring and tuning high-performance and high-availability systems (see Section 4.1)

• Applying configuration-specific tuning guidelines (Section 4.2)

• Running sys_check and applying its configuration and tuning guidelines (Section 4.3)

• Identifying and solving some common performance problems (Section 4.4)

• Using the advanced tuning guidelines described in this manual (Section 4.5)

4.1    Steps for Configuring and Tuning Systems

Before you configure and tune a system, you must become familiar with the terminology and concepts relating to performance and availability. See Chapter 1 for information.

In addition, you must understand how your applications utilize system resources, because not all configurations and tuning guidelines are appropriate for all types of workloads. For example, you must determine if your applications are memory-intensive or CPU-intensive, or if they perform many disk or network operations. See Section 2.1 for information about identifying a resource model for your configuration.

To help you configure and tune a system that will meet your performance and availability needs, follow these steps:

1. Ensure that your hardware and software configuration is appropriate for your workload resource model and your performance and availability goals. See Chapter 2.

2. Make sure that you have adhered to the configuration guidelines for:

   • Memory and swap space (Section 2.3.2)

   • Disks, LSM, and hardware RAID (Chapter 8)

   • AdvFS, UFS, and NFS file systems (Chapter 9)

3. Perform the following initial tuning tasks:

   1. If you have a large-memory system, Internet server, or NFS server, follow the tuning guidelines that are described in Section 4.2.

   2. Apply any tuning recommendations described in your application documentation.

   3. Make sure that you have sufficient system resources for large applications or for large-memory systems. See Chapter 5 for information about resource tuning.

   4. Run sys_check and consider following its configuration and tuning recommendations (see Section 4.3).

4. Monitor the system and evaluate its performance, identifying any areas in which performance can be improved. Section 3.4 describes the tools that you can use to monitor performance.

5. If performance is deficient, see Section 4.4 for information about solving common performance problems, and see Section 4.5 for information about using the advanced tuning guidelines.

System tuning usually involves modifying kernel subsystem attributes. See Section 3.6 for information.

4.2    Tuning Special Configurations

Large configurations or configurations that run memory-intensive or network-intensive applications may require special tuning. The following sections provide information about tuning these special configurations:

• Internet servers (Section 4.2.1)

• Large-memory servers (Section 4.2.2)

• NFS servers (Section 4.2.3)

In addition, your application product documentation may include specific configuration and tuning guidelines that you should follow.

4.2.1    Tuning Internet Servers

Internet servers (including Web, proxy, firewall, and gateway servers) run network-intensive applications that usually require significant system resources. If you have an Internet server, it is recommended that you modify the default values of some kernel attributes.

Follow the guidelines in Table 4-1 to help you tune an Internet server.

Table 4-1:  Internet Server Tuning Guidelines

4.2.2    Tuning Large-Memory Systems

Large memory systems often run memory-intensive applications, such as database programs, that usually require significant system resources. If you have a large memory system, it is recommended that you modify the default values of some kernel attributes.

Follow the guidelines in Table 4-2 to help you tune a large-memory system.

Table 4-2:  Large-Memory System Tuning Guidelines

4.2.3    Tuning NFS Servers

NFS servers run only a few small user-level programs, which consume few system resources. File system tuning is important because processing NFS requests consumes the majority of CPU and wall clock time. See Chapter 9 for information on file system tuning.

In addition, if you are running NFS over TCP, tuning TCP may improve performance if there are many active clients. See Section 10.2 for information on network subsystem tuning. If you are running NFS over UDP, network subsystem tuning is not needed.

Follow the guidelines in Table 4-3 to help you tune a system that is only serving NFS.

Table 4-3:  NFS Server Tuning Guidelines

4.3    Checking the Configuration by Using the sys_check Utility

After you apply any configuration-specific tuning guidelines, as described in Section 4.2, run the sys_check utility to check your system configuration.

The sys_check utility creates an HTML file that describes the system configuration, and can be used to diagnose problems. The utility checks kernel attribute settings and memory and CPU resources, provides performance data and lock statistics for SMP systems and for kernel profiles, and outputs any warnings and tuning guidelines.

Consider applying the sys_check utility's configuration and tuning guidelines before applying any advanced tuning guidelines.

Note

You may experience impaired system performance while running the sys_check utility. Invoke the utility during offpeak hours to minimize the performance impact.

You can invoke the sys_check utility from the SysMan graphical user interface or from the command line. If you specify sys_check without any command-line options, it performs a basic system analysis and creates an HTML file with configuration and tuning guidelines. Options that you can specify at the command line include the following:

• The -all option provides information about all subsystems, including security information and setld inventory verification.

• The -perf option provides only performance data and excludes configuration data.

• The -escalate option creates escalation files required for reporting problems to Compaq.

See sys_check(8) for more information.

4.4    Solving Common Performance Problems

The following sections provide examples of some common performance problems and solutions:

• Slow application performance (Section 4.4.1)

• Insufficient memory or excessive paging (Section 4.4.2)

• Insufficient swap space (Section 4.4.3)

• Swapped out processes (Section 4.4.4)

• Insufficient CPU cycles (Section 4.4.5)

• Disk bottleneck (Section 4.4.6)

• Poor disk I/O performance (Section 4.4.7)

• Poor AdvFS performance (Section 4.4.8)

• Poor UFS performance (Section 4.4.9)

• Poor NFS performance (Section 4.4.10)

• Poor network performance (Section 4.4.11)

Each section describes how to detect the problem, the possible causes of the problem, and how to eliminate or diminish the problem.

4.4.1    Application Completes Slowly

Use the following table to detect a slow application completion time and to diagnose the performance problem:

4.4.2    Insufficient Memory or Excessive Paging

A high rate of paging or a low free page count may indicate that you have inadequate memory for the workload. Avoid paging if you have a large memory system. Use the following table to detect insufficient memory and to diagnose the performance problem:

4.4.3    Insufficient Swap Space

If you consume all the available swap space, the system will display messages on the console indicating the problem. Use the following table to detect if you have insufficient swap space and to diagnose the performance problem:

4.4.4    Processes Swapped Out

Swapped out (suspended) processes will decrease system response time and application completion time. Avoid swapping if you have a large memory system or large applications. Use the following table to detect if processes are being swapped out and to diagnose the performance problem:

4.4.5    Insufficient CPU Cycles

Although a low CPU idle time can indicate that the CPU is being fully utilized, performance can suffer if the system cannot provide a sufficient number of CPU cycles to processes. Use the following table to detect insufficient CPU cycles and to diagnose the performance problem:

4.4.6    Disk Bottleneck

Excessive I/O to only one or a few disks may cause a bottleneck at the overutilized disks. Use the following table to detect an uneven distribution of disk I/O and to diagnose the performance problem:

4.4.7    Poor Disk I/O Performance

Because disk I/O operations are much slower than memory operations, the disk I/O subsystem is often the source of performance problems. Use the following table to detect poor disk I/O performance and to diagnose the performance problem:

4.4.8    Poor AdvFS Performance

Use the following table to detect poor AdvFS performance and to diagnose the performance problem:

4.4.9    Poor UFS Performance

Use the following table to detect poor UFS performance and to diagnose the performance problem:

4.4.10    Poor NFS Performance

Use the following table to detect poor NFS performance and to diagnose the performance problem:

4.4.11    Poor Network Performance

Use the following table to detect poor network performance and to diagnose the performance problem:

4.5    Using the Advanced Tuning Guidelines

If system performance is still deficient after applying the initial tuning recommendations (Section 4.1) and considering the solutions to common performance problems (Section 4.4), you may be able to improve performance by using the advanced tuning guidelines. Advanced tuning requires an in-depth knowledge of Tru64 UNIX and the applications running on the system, and should be performed by an experienced system administrator.

Before using the advanced tuning guidelines, you must:

• Understand your workload resource model, because not all tuning guidelines are appropriate for all configurations (see Section 2.1)

• Gather performance information to identify an area in which to focus your efforts (see Section 3.4 for information on using commands to obtain a basic understanding of system performance)

Use the advanced tuning guidelines shown in Table 4-4 to help you tune your system. Before implementing any tuning guideline, you must ensure that it is appropriate for your configuration and workload and also consider its benefits and tradeoffs.

Table 4-4:  Advanced Tuning Guidelines