CPU scheduling in Version 4+

DEPRECATED

Time-slicing

Starting with version 4.00, the BOINC core client does time-slicing. This means that the core client may switch back and forth between results of different projects. This is done in a way that allocates CPU time according to the 'resource shares' you have assigned to each project.

For example, suppose you participate in SETI@home with resource share 100 and Predictor@home with resource share 200. A single-processor machine might be scheduled as follows:

1:00 - 2:00: SETI@home
2:00 - 3:00: Predictor@home
3:00 - 4:00: Predictor@home
4:00 - 5:00: SETI@home
5:00 - 6:00: Predictor@home
6:00 - 7:00: Predictor@home
...

A two-processor machine might be scheduled as follows:

             CPU 0             CPU 1
1:00 - 2:00: Predictor@home    SETI@home
2:00 - 3:00: Predictor@home    SETI@home
3:00 - 4:00: Predictor@home    Predictor@home
4:00 - 5:00: Predictor@home    SETI@home
5:00 - 6:00: Predictor@home    SETI@home
6:00 - 7:00: Predictor@home    Predictor@home

In every 3 hour period, your computer spends 4 hours on Predictor@home and 2 hours on SETI@home, which is the desired ratio.

This feature is necessary to handle projects like Climateprediction.net, whose work units take a long time (1 or 2 months) to complete on a typical computer. Without time-slicing, your computer would have to finish an entire work unit before it could start working on a different project.

Preemption

When BOINC switches from one application to another, the first application is said to be preempted. BOINC can do preemption in two different ways; you can select this as part of your General Preferences.

Don't leave the suspended applications in memory (default). Applications are preempted by killing them; they are later restarted, and resume from their last checkpoint. This saves virtual memory (swap space) but can waste CPU time, especially if applications checkpoint infrequently.
Leave suspended applications in memory. Applications are preempted by suspending them; they remain in virtual memory while preempted (they don't necessarily occupy physical memory).

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