Hi, Daniel, I'm not a scheduler expert by any stretch, but I can try to play one on the net... > I'm following the Robert Love's book and am trying to understand the > Linux O(1) scheduler. Note that the O(1) scheduler is no more; it was replaced by the completely fair scheduler in 2.6.23. For the purposes of your questions things haven't changed a lot, but it's completely different internally. > So here is my understanding. The kernel allows > the applications to specify two types of priorities > > * Realtime Priorities: Range from 0 to 99 > * Non-realtime priorities: Also called "nice" values range from -20 to +19. You're really talking about different scheduling classes. There are two realtime classes (FIFO and RR), both of which trump the interactive class (SCHED_OTHER). > * A total of 140 priorities (100 RT + 40 non-RT) - these priorities > are static - do not change over time. Sort of, but realtime priorities are really an entirely different scale. > * A lower priority process will run only if there are no runnable > processes in priority above it - this automatically means that all RT > processes get to run before non-RT processes. That is true for the realtime classes. SCHED_OTHER will give lower-priority processes a bit of time even in the presence of runnable high-priority processes. > * tasks on the same priority level are scheduled round robin SCHED_RR does that, SCHED_FIFO does not. SCHED_OTHER is fairness-based, which has RR-like characteristics but is not quite the same. Hope that helps, jon Jonathan Corbet / LWN.net / corbet@xxxxxxx -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
