Problems with OS X Files: Open, Copy, Delete, and Beyond

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"Technically Speaking: Monitoring and Improving Performance," later in this chapter, for more information on memory and the swap file.

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Chapter 8 for more information on Internet issues.

TECHNICALLY SPEAKING

Monitoring and Improving Performance

Insufficient memory, too slow a processor (CPU), a nonoptimized drive—all these things (and more) can decrease the performance of Mac OS X. But if you suspect that your Mac is not up to par, how would you determine which, if any, of these factors is the major cause? And beyond adding hardware (such as more memory or a faster processor), what, if anything, can you do to improve performance? The answers to both of these questions reside in a host of utility software. Some solutions require using Terminal; others are Aqua-based. Following is an overview.

CPU Monitor. CPU Monitor, which is included when you install Mac OS X, is located in the Utilities folder. When you launch it, the program displays a small thermometer-type gauge, with a current level that keeps rising and falling. The level indicates the ever-changing extent of CPU use. Don't be alarmed if the level occasionally gets to 100 percent; that's OK as long as it doesn't stay there for a sustained period. If the gauge remains at its peak, you are likely trying to do too many processor-intensive activities at the same time. Quitting some applications or reducing how many tasks you have going simultaneously will likely help. I have rarely found this gauge to be diagnostically useful. But the CPU Monitor Processes menu also serves as a convenient launch pad for two more-useful functions: Process Viewer and top.

ProcessViewer. ProcessViewer is also part of the basic Mac OS X installation. I have discussed this utility before, primarily in Chapter 5, as a means to force-quit processes. Now I want to focus on two additional features of the utility: its %CPU and %Memory column listings. Each process listed in ProcessViewer's display has a value in each of these two columns. These values indicate how much CPU attention and memory availability the process is using. You can sort either column by clicking the column name. If you do so, the processes that move to the top are the ones that are the most likely culprits in any CPU- or memory-related performance problems. In general, regardless of what the results may be, do not quit any processes that you do not recognize, especially administrative processes. If a process name is for an application you do know, its CPU or memory percentage remains high, and you don't need it open at the moment, quitting that application would be a good idea.

One difficulty is that all Carbon applications will have the name LaunchCFMApp, making it dif-ficult to tell which one represents a particular Carbon application. Similarly, Classic applications are not listed separately but are included under the TruBlueEnvironme process. You may need to do trial-and-error guesswork to figure out the culprit.

Also note: Some applications may claim to be using 0 percent of memory. This can happen; it does not mean that something is wrong.

Terminal commands. You can view (and, in some cases, modify) a variety of important performance measures via Unix commands you enter in Terminal. Following are some examples:

• top. If you choose the top command in CPU Monitor, it will launch Terminal and execute. You can also get there simply by launching Terminal and typing <top>. The top display is Unix's version of ProcessViewer. The PID column, for example, gives the Process ID number for a process, the Command column gives the name of each process, and the %CPU gives current CPU use. The numbers continue to update as you watch. To exit this display, type

  <q> (for quit).

  NOTE

  Note: Unlike ProcessViewer, Terminal does not list the names of all Carbon applications as LaunchCFMApp.

  At the top of the top display are some other important numbers. Load Avg is one indication of CPU use. The three numbers represent the most recent average and two averages from minutes before. Generally, the load should stay below 2.0. If it gets higher and stays there, and if performance slows, you may be trying to do something beyond what the processor can handle. If what you are trying to do is essential to your work, an upgrade to a faster processor may be required. Otherwise, you need to try to do less at the same time.

  The CPU Usage numbers give a different perspective on how the CPU is being used. These numbers indicate how much of the CPU is allocated to the system (kernel) vs. the user vs. how much is not currently being used at all (idle). Be especially on guard as the idle percentage approaches 0, which is likely to correlate with performance slowdowns.

  Finally, the VM (virtual memory) line gives an indication of memory use. The VM line looks something like this:

  VM: 3.19G + 50.7M 25092(0) pageins, 24969(0) pageouts 

  If the initial number (3.19 GB in the preceding example) is getting close to the size of your remaining free hard-drive space, you are likely to see performance slowdowns. This number indicates that your swap file does not have sufficient space. (Note: The amount of free space on your volume is listed in the status bar of any Finder window for that volume, assuming that Show Status Bar was chosen from the Finder's View menu.) For further details on memory use, read on.

• vmstat. Unix's vmstat command provides a more focused look at Mac OS X's memory use than top provides. Of particular interest is the number of pageouts (also listed in the top display). The pageout value is an indication that physical memory is being paged (swapped) to the swap file on your drive. The higher the number of pageouts, the greater the disk access and the worse your performance is likely to be. A performance problem is especially indicated if you see pageouts continuing to increase over time.

  If pageouts equal 0, you are not using the swap file at all. This situation is the ideal, as any use of the swap file will likely result in slower performance. As long as the pageout number is near 0 and relatively stable, you need not be too concerned about memory use, even if other statistics indicate that your memory use is at or near 100 percent.

• renice. As I discussed earlier in this book (see "Darwin" in Chapter 4), Mac OS X's preemptive multitasking attempts to allocate the processor's attention such that the most important tasks get the most attention (generally giving greater attention to a foreground application over a background one, for example). Tasks that get the greatest attention complete the fastest. One way the OS makes these decisions is by assigning each process a priority ranking. When two processes are competing for the CPU's attention, the one with the greater priority will receive the greater attention.

  On occasion, however, you may want to override the OS's default priorities. Some users have found they can give Virtual PC a needed speed boost by assigning a higher priority to it. To do this, you use Terminal's renice command. The default nice level for most applications is 0. The potential range is between –20 and +20. To increase an application's priority, you lower its nice level from 0 to a lower number. (The lower the number, the more attention a process gets.) There are limits, of course. If you give everything a score of -20, for example, you won't be increasing the performance of anything. The benefits are always relative to the priorities assigned to other processes.

  To change a nice value, type <sudo renice {nice #} {pid}>, in which where {nice #} is the integer from –20 to +20 and {pid} is the process ID number of the process you want to change. (You can determine a process pid from the top command or from ProcessViewer.) Unfortunately, these changes may not be saved after you quit the application or restart the Mac. So you may need to reenter a change each time you use the application.

  By the way, users have noticed that Virtual PC runs slower in Mac OS X than it does in Mac OS 9. Connectix claims that this slowdown is due to a rare case in which preemptive multitasking (used in Mac OS X but not Mac OS 9) turns out to be a disadvantage. In Mac OS 9, Connectix can make sure that Virtual PC gets as much processor priority as possible. In Mac OS X, preemptive multitasking prevents this situation, resulting in slower performance. An upgrade to Mac OS X is supposed to provide a workaround for this situation.

• Optimize (update_prebinding). When you run a Mac OS X update via the Installer utility, at some point, the Installer typically says that it is optimizing the software. This process often turns out to be the longest part of the entire update.

  What the Installer is doing at this point is running the Unix update_prebinding command. To explain the process in the most nontechnical language possible, the command updates the linking among applications and the shared library files that may be required to run an application. Whenever a new application is installed, this information map needs to be updated. If the information is not updated, the resolving of these links is calculated when you launch the application, which takes added time and thus slows performance. Installers perform this task because, following the installation of new software, updating this map is desirable.

  If you add applications to your drive by any method that does not do this updating (which would be the case for most applications that do not use Apple's Installer utility), running the update_prebinding command yourself could increase the speed of Mac OS X.

  The simplest way to do this is to bypass Terminal and use Xoptimize, an Aqua-based utility that accesses the same update_prebinding command. Xoptimize also includes options (such as using less memory when running the optimization) that can prevent problems that might occur if you simply ran update_prebinding from Terminal.

  NOTE

  Mac OS 9 users may be familiar with the term optimizing, as it refers to defragment-ing the files on a disk and optimizing their locations as done via a utility such as Norton Utilities' Speed Disk. This process is different from the Unix-based optimization referred to in this sidebar. You may still get benefit from using Speed Disk on a Mac OS X volume, but I confess that I no longer bother to do this. The process is not likely to be of much value if you have a large hard dive with a good deal of unused space. The issue did come up, however, when I decided whether to move the swap file to a separate partition (see: "Technically Speaking: Moving the Swap File to a Separate Partition" earlier in this chapter).

• netstat. Terminal's netstat command gives you a quick indication of whether your network connection is performing up to par. In Terminal, type <netstat –i>. In the display that appears, if the incoming packet count is 0, you probably don't have a connection at all. If your error count is greater than 1 to 2 percent, there is likely to be some problem with your connection (perhaps a network difficulty at your cable company's end). Type <netstat -i 10>, and the display is updated every 10 seconds. This technique allows you to test hypotheses. You could start your browser to see whether the error counts change as the browser attempts a connection, for example.

Aqua-based utilities. Many Aqua-based utilities that measure performance are actually graphical user interfaces (or GUIs) for a Unix function otherwise accessed via Terminal. I have already mentioned some of the utilities, including ProcessViewer, CPU Monitor, and Xoptimize. Following are some others.

Perfboard is an Aqua-based shareware utility that provides a quick view of most of the data covered in this sidebar. In its default view, you get a constantly updated look at CPU percentage, system load, memory use (including pageouts), network ins and outs, and disk reads and writes.

Other Aqua-based utilities provide similar feedback—usually, a subset of what Perfboard provides, but in the form of a menu-bar item or a Dock icon. One example is GMem!, which shows memory use.

The Renicer and Nicer utilities allow you to modify the nice level of a process without using Terminal.

The Netstat tab of Network Utility (included in the Utilities folder of Mac OS X) offers similar functionality to Unix's netstat command.

Figure 6.46 CPU Monitor's Processes menu and CPU gauge.

Figure 6.47 Process Viewer's display.

Figure 6.48 The top command output viewed in Terminal.

Figure 6.49 The vm_stat command output viewed in Terminal.