"Nice %" on Activity Monitor

Hi

Nice normally refers to processes that are running at a priority lower than the default (and are therefore 'nice' to other processes). When the CPUs are under heavy load, I think it's possible for applications to renice themselves automatically, so they have a lower priority and more CPU cycles are available to the higher priority processes. It may be that the Activity Monitor renices itself, in affect giving up CPU cycles to more important applications.

The 'nice %' shows the amount of CPU being used by processes which have had their scheduling priority reduced.

Hmm I was wondering about that as well. Interesting. So what is this information about niced CPU cycles typically used for?

nice is a Unix command which allows processes to be run with a scheduling priority different from the default. renice allows the scheduling priority of existing processes to be adjusted.

If you run Terminal in the Applications\Utilities folder and type

man nice

or

man renice

at the command prompt, the manual for the nice and renice commands will be displayed.

Typically important processes will have a low nice value (hence high scheduling priority), unimportant processes will have a high nice value (hence low scheduling priority).

I've never used SETI At Home or similar applications but they'd be a good example. Ideally they should be running all the time but not intefer with your real day to day work, hence they should have a high nice value so they only use 'spare' CPU cycles. Also I wouldn't be surprised if the Activity Monitor renices itself, as it would be ironic if the tool used to monitor activity results in significant activity itself (at the expense of the other processes).

In theory you could use the nice % information to adjust the scheduling priority of the processes.

Activity Monitor doesn't 'nice' itself, verified with 'ps lax' in Terminal.