Messages in this thread | | | Date | Wed, 19 Nov 2008 09:21:46 -0800 | Subject | Re: [patch] sched: add locking when update the task_group's cfs_rq[] array. | From | Ken Chen <> |
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On Wed, Nov 19, 2008 at 8:54 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Tue, 2008-11-18 at 22:48 -0800, Ken Chen wrote: >> add locking when update the task_group's cfs_rq[] array. tg_shares_up() >> can be potentially executed concurrently on multiple CPUs with overlaping >> cpu mask depending on where task_cpu() was when a task got woken up. Lack >> of any locking while redistribute tg->shares over cfs_rq[] array opens up >> a large window for conflict updates and utimately cause corruptions to the >> integrity of per cpu cfs_rq shares. Add a tg_lock to protect the operations. > > I see why you want to do this, but introducing a global lock makes me > sad :/
I wholly agree on the scalability. The bigger the system, the more it needs to protect the integrity of cfs_rq[]->shares that the sum still adds up to tg->shares. Otherwise, the share distributed on each CPU's cfs_rq might go wildly and indirectly leads to fluctuation of effective total tg->shares. However, I have the same doubt that this will scale on large CPU system. Does CFS really have to iterate the whole task_group tree?
- Ken
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