Messages in this thread | | | Subject | Re: [RFC PATCH 14/14] sched: implement usage tracking | From | Peter Zijlstra <> | Date | Mon, 20 Feb 2012 17:30:02 +0100 |
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On Fri, 2012-02-17 at 03:32 -0800, Paul Turner wrote:
> Since we do not know where we slept relative to the tick, unless we > explicitly track where this occurred we don't know for a "n.y" jiffy > sleep whether the "0.y" fraction included an extra decay.
but isn't that the same problem you have in __update_entity_runnable_avg() where you use ->runnable_avg_period % 1024 ?
Also, shouldn't __synchronize_entity_decay() update ->runnable_avg_period? Surely when you wake up your window fraction could be different than when you went to sleep?
> It's > important to get this right to reduce instability, since when the > entity wakes back up we need to charge an equivalent decay against > it's contribution before we can remove it from the blocked_load_sum. > > For the common case of a short sleep whether we charge an extra period > (if y included a jiffy edge) or not is significant to stability since > getting it wrong means we leave a little extra load in blocked_load.
Sure..
> Further complicating this we need to be able to do said > synchronization in the annoying cases of wake-up migration (where we > don't hold the lock on previous rq) and 32-bit machines (where > everything sucks).
Ah, wouldn't task_waking_fair() be a better place though?
> > > > C) 'Migrate' > > - uses contributes_blocked_load to check if we actually did migrate? > > > > We actually use se->avg.decay_count to check whether we were migrated > (setting it appropriately at migration); contributes_blocked_load is > just a convenience variable to track whether we're a part of > cfs_rq->blocked_load_avg or not.
If you use task_waking_fair() you can also use ENQUEUE_WAKING.
> There's a one or two other paths (than ttwu) that this matters for, > using set_task_rq() gets them all.
What paths are those? Having a cfs hook in the generic code there isn't pretty an suggests funny things could happen when PI gets done.
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