sched/deadline: Add SCHED_DEADLINE SMP-related data structures & logic
Introduces data structures relevant for implementing dynamic migration of -deadline tasks and the logic for checking if runqueues are overloaded with -deadline tasks and for choosing where a task should migrate, when it is the case. Adds also dynamic migrations to SCHED_DEADLINE, so that tasks can be moved among CPUs when necessary. It is also possible to bind a task to a (set of) CPU(s), thus restricting its capability of migrating, or forbidding migrations at all. The very same approach used in sched_rt is utilised: - -deadline tasks are kept into CPU-specific runqueues, - -deadline tasks are migrated among runqueues to achieve the following: * on an M-CPU system the M earliest deadline ready tasks are always running; * affinity/cpusets settings of all the -deadline tasks is always respected. Therefore, this very special form of "load balancing" is done with an active method, i.e., the scheduler pushes or pulls tasks between runqueues when they are woken up and/or (de)scheduled. IOW, every time a preemption occurs, the descheduled task might be sent to some other CPU (depending on its deadline) to continue executing (push). On the other hand, every time a CPU becomes idle, it might pull the second earliest deadline ready task from some other CPU. To enforce this, a pull operation is always attempted before taking any scheduling decision (pre_schedule()), as well as a push one after each scheduling decision (post_schedule()). In addition, when a task arrives or wakes up, the best CPU where to resume it is selected taking into account its affinity mask, the system topology, but also its deadline. E.g., from the scheduling point of view, the best CPU where to wake up (and also where to push) a task is the one which is running the task with the latest deadline among the M executing ones. In order to facilitate these decisions, per-runqueue "caching" of the deadlines of the currently running and of the first ready task is used. Queued but not running tasks are also parked in another rb-tree to speed-up pushes. Signed-off-by:Juri Lelli <juri.lelli@gmail.com> Signed-off-by:
Dario Faggioli <raistlin@linux.it> Signed-off-by:
Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1383831828-15501-5-git-send-email-juri.lelli@gmail.comSigned-off-by:
Ingo Molnar <mingo@kernel.org>
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