Re: [PATCH 2/2] sched: update runqueue clock before migrations away

[Peter Zijlstra]

On Tue, Dec 10, 2013 at 01:24:21PM +0000, Chris Redpath wrote:
> What happens is that if you have a task which sleeps for a while and wakes
> on a different CPU and the previous CPU hasn't had a tick for a while, then
> that sleep time is lost.

/me more confused now.

Where does update_cfs_rq_blocked_load() account sleep time? Its only
concerned with the blocked decay.

Or is it the decay_count <= 0 case in enqueue_entity_load_avg() that's
screwing you over?

That's guestimating the last_runnable_update based on decay_count, and
per the previous the decay count can get slightly out of sync.

If so, we should look to cure the issue enqueue_entity_load_avg() is
trying to work around, namely the fact that we cannot assume synced
clocks, nor can we read remote clocks atomically.



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