Hi,
perhaps someone can give me a hint what I should consider to look for in
order to change the ("old" 2.6.21) scheduler such that it schedules the
highest priority task of a given runqueue.
Given a multiprocessor system I currently observe that whenever there
are two tasks on one CPU, the lower priority one is migrated to another
CPU. But I don't realize why this happens. From looking at the source
code I thought it should be the highest priority one (lowest bit set in
the runqueue's bitmap) according to
idx = sched_find_first_bit(array->bitmap);
within move_tasks(). The idx value is then used as an index (surprise)
to the linked list of tasks of this particular priority and one task is
picked:
head = array->queue + idx;
curr = head->prev;
tmp = list_entry(curr, struct task_struct, run_list);
Is my assumption wrong? Using printk()s within this code section makes
the system just hang completely quite soon. The schedstats do not notify
me immediately. So I am a bit lost on how to track down or trace the
problem.
Can anybody confirm that my observations are correct that the scheduler
picks the lowest priority job of a runqueue for migration?
What needs to be changed in order to pick the highest priority one?
Martin
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