Setting budgets for resource managers
Ideally we'd like resource managers, such as filesystems, to run with a budget of zero. That way they'd always be billing time to their clients. However, some device drivers realize too late which client a particular thread was doing work for. Consequently, some device drivers may have background threads for audits or maintenance that require CPU time that can't be attributed to a particular client. In those cases, you should measure the resource manager's background and unattributable loads, and then add that amount to its partition's budget.
- If your server has maintenance threads that never serve clients, then it should be in a partition with a nonzero budget.
- If your server communicates with its clients by sending messages, or by using mutexes or shared memory (i.e., anything other than receiving messages), then your server should be in a partition with a nonzero budget.
You can set the size of the time-averaging window to be from 8 to 400 milliseconds. This is the time over which the thread scheduler attempts to balance scheduler partitions to their guaranteed CPU limits. Different choices of window sizes affect both the accuracy of load balancing and, in extreme cases, the maximum delays seen by ready-to-run threads.