Idle Detection

The following settings determine the way in which the operating system detects that an application in a VDM is currently idle. These settings should be used when an application exhibits poor performance, or where mouse movement in a DOS application is "jerky".

IDLE_SECONDS

Function:

When programs appear to be doing nothing but waiting for input, the operating system gives them less time to run. This is done to give preference to programs that are doing useful work. Some programs periodically appear to be waiting for input, but then change their behavior and continue after a time. This setting disables the "IDLE_SENSITIVITY" function for a period of time after useful work has been detected.

Also see IDLE_SENSITIVITY below for more details on idle detection.

If a program appears to run slowly when there is an option for the user to provide input, this value should be increased.

Setting the value too high gives the DOS program more resources than it needs.

This value is in seconds. The default is no idle time allowed.

The setting can be changed while the program is running to tune it to the proper value.

A game may pause, for instance, to wait for the user to make a choice, but then continues if the user does not react.

When DOS 5 is run in a virtual machine boot session, (See Virtual Machine Boot) the DOS shell may fail to complete displaying the directory of the C: drive if IDLE_SENSITIVITY is set too low. IDLE_SECONDS should then be raised.

IDLE_SENSITIVITY

Function:

The idle sensitivity level sets a threshold for judging when applications will be considered idle. The value is the percentage of the maximum possible polling rate the application can perform. If an application polls at a rate higher than this value, it is considered "idle".

DOS programs often "poll" for input when they are waiting for a user response. For instance, a program may wait for a response by repeatedly checking to see if the user has hit a key. In a multitasking environment such as OS/2 Version 2.0, this wastes time when other programs could be running instead. The operating system detects idle programs by looking for a high rate of polling for input. When programs are judged to be waiting for input, they are given less time to run.

For example, if idle sensitivity is set to 75%, then an application repeatedly checking to see if input is available would have to do this checking at more than 75% of the maximum possible rate before it would be judged idle.

Idle detection is a "best guess" of what the program is doing. It could be that the program is polling at a very high rate, but is still doing useful work in between checking. It may be that the application checks at a fairly slow rate but still is doing nothing but waiting. The idle sensitivity threshold allows adjustment of the threshold for a particular application.

Also see IDLE_SECONDS above.

Advantages:
If an application receives input while running and seems to run slower than expected, the idle sensitivity should be set to a higher value. This lets the application poll at a higher rate without being judged idle. Setting the level to 100 turns idle detection off altogether. The application will be allowed to poll for input as often as it likes.

If an application is waiting for input and other applications do not appear to be running, the idle sensitivity should be adjusted downward. This lowers the threshold for judging the application idle.

Default:
The default is 75%.
Settable:
The setting can be changed while the program is running to tune it to the proper value.
Examples:
Overall system performance can usually be improved when there are multiple DOS applications running if IDLE_SENSITIVITY is turned down.

Also see Dos Environment (DOS_BACKGROUND_EXECUTION).

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