[PATCH] sched: Avoid unnecessarily moving highest priority task move_tasks()
Problem: To help distribute high priority tasks evenly across the available CPUs move_tasks() does not, under some circumstances, skip tasks whose load weight is bigger than the designated amount. Because the highest priority task on the busiest queue may be on the expired array it may be moved as a result of this mechanism. Apart from not being the most desirable way to redistribute the high priority tasks (we'd rather move the second highest priority task), there is a risk that this could set up a loop with this task bouncing backwards and forwards between the two queues. (This latter possibility can be demonstrated by running a nice==-20 CPU bound task on an otherwise quiet 2 CPU system.) Solution: Modify the mechanism so that it does not override skip for the highest priority task on the CPU. Of course, if there are more than one tasks at the highest priority then it will allow the override for one of them as this is a desirable redistribution of high priority tasks. Signed-off-by: NPeter Williams <pwil3058@bigpond.com.au> Cc: Ingo Molnar <mingo@elte.hu> Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com> Signed-off-by: NAndrew Morton <akpm@osdl.org> Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
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