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Monitoring CPU and CPU Core Usage
Last updated June 01, 2009 - Send Feedback
Note: Activity Monitor in OS X Mavericks has changed in appearance and certain terminology. See Using Activity Monitor in OS X Mavericks.
The graphical displays provided by Activity Monitor are excellent.
is found in the folder under . Drag it into the dock so that it’s always readily available. Especially on dual display systems, it can be left open on the 2nd monitor for conveniently monitoring system performance.
Percentage CPU usage
Sometimes you want to know which program is using the most CPU time. The mainwindow shows processes and various information about them.
Choosein the popup menu at center. Control-click or right-click on column headers to choose which columns to display. Note that the column names are abbreviated when the window size is reduced.
Sort by percentage CPU usage by clicking on the MemoryTester (dlt) test in progress, taking 364.7% of the available CPU cycles. The remainder is being used by WindowServer, DreamWeaver, etc. One CPU core represents 100%, 2 CPU cores is 200%, etc.column (triangle should point down as shown). This makes it easy to see which applications are using CPU resources. The example below shows a
You might find that some “vampire” programs waste CPU time when doing nothing useful— these are programs you don’t want to leave running when you’re not using them!
Disk and network activity
Observe the tabs at bottom (/ etc). These show other useful information. Unfortunately, they can be shown only one tab at a time (you can’t watch and at the same time).
CPU history graph
The history graph () can be sized wider to show CPU history over quite some time ( ). Black areas indicate idle CPU cores. Green represents CPU utilization by user applications, red represents CPU utilization by Mac OS X itself, and blue indicates low-priority tasks. The example below shows a mostly idle system.
Make sureis disabled (unchecked).
The display updates as specified, scrolling left at each interval. Watch this display for your favorite programs, and you can see how well (or poorly) they utilize the CPU cores while doing some hard work, like Unsharp Mask in Photoshop.
For a dual-core system, you’ll see two layers, four layers for 4-core-, eight for 8-core, etc. When we have 32 cores, let’s wait and see what Apple does!
Command line tools for monitoring CPU and memory usage
Monitoring performance in Terminal (a plain-text display) can be useful; it is mentioned here for completeness.
The top and vm_stat tools (and iostat for disk I/O) can come in handy. You must use these tools in a window. The most useful tool is top, which can be left running continually, refreshing the window at regular intervals.
Show top 10 processes by CPU usage every 2 seconds: top -o cpu -s 2 10
Show top 10 processes by real memory every 2 seconds: top -o rsize -s 2 10
The vm_stat tool also provides some useful statistics: