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authorNick Piggin <nickpiggin@yahoo.com.au>2005-06-25 14:57:07 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-25 16:24:40 -0700
commit8102679447da7fcbcb5226ee0207c3a034bc6d5f (patch)
treebb1717150a94a02a44c3bafc9bf8969ef6045f89 /init
parente0f364f4069f76a3613a797c388832822d179076 (diff)
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[PATCH] sched: improve load balancing pinned tasks
John Hawkes explained the problem best: A large number of processes that are pinned to a single CPU results in every other CPU's load_balance() seeing this overloaded CPU as "busiest", yet move_tasks() never finds a task to pull-migrate. This condition occurs during module unload, but can also occur as a denial-of-service using sys_sched_setaffinity(). Several hundred CPUs performing this fruitless load_balance() will livelock on the busiest CPU's runqueue lock. A smaller number of CPUs will livelock if the pinned task count gets high. Expanding slightly on John's patch, this one attempts to work out whether the balancing failure has been due to too many tasks pinned on the runqueue. This allows it to be basically invisible to the regular blancing paths (ie. when there are no pinned tasks). We can use this extra knowledge to shut down the balancing faster, and ensure the migration threads don't start running which is another problem observed in the wild. Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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