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- Add an IPI based mechanism for migrating kses. This mechanism is broken down into several components. This is intended to reduce cache thrashing by eliminating most cases where one cpu touches another's run queues. - kseq_notify() appends a kse to a lockless singly linked list and conditionally sends an IPI to the target processor. Right now this is protected by sched_lock but at some point I'd like to get rid of the global lock. This is why I used something more complicated than a standard queue. - kseq_assign() processes our list of kses that have been assigned to us by other processors. This simply calls sched_add() for each item on the list after clearing the new KEF_ASSIGNED flag. This flag is used to indicate that we have been appeneded to the assigned queue but not added to the run queue yet. - In sched_add(), instead of adding a KSE to another processor's queue we use kse_notify() so that we don't touch their queue. Also in sched_add(), if KEF_ASSIGNED is already set return immediately. This can happen if a thread is removed and readded so that the priority is recorded properly. - In sched_rem() return immediately if KEF_ASSIGNED is set. All callers immediately readd simply to adjust priorites etc. - In sched_choose(), if we're running an IDLE task or the per cpu idle thread set our cpumask bit in 'kseq_idle' so that other processors may know that we are idle. Before this, make a single pass through the run queues of other processors so that we may find work more immediately if it is available. - In sched_runnable(), don't scan each processor's run queue, they will IPI us if they have work for us to do. - In sched_add(), if we're adding a thread that can be migrated and we have plenty of work to do, try to migrate the thread to an idle kseq. - Simplify the logic in sched_prio() and take the KEF_ASSIGNED flag into consideration. - No longer use kseq_choose() to steal threads, it can lose it's last argument. - Create a new function runq_steal() which operates like runq_choose() but skips threads based on some criteria. Currently it will not steal PRI_ITHD threads. In the future this will be used for CPU binding. - Create a kseq_steal() that checks each run queue with runq_steal(), use kseq_steal() in the places where we used kseq_choose() to steal with before.
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