Re: [PATCH 4/5] sched/fair: Remove double_lock_balance() from active_load_balance_cpu_stop()

From: Tim Chen
Date: Thu Jul 24 2014 - 20:04:37 EST

On Tue, 2014-07-22 at 15:30 +0400, Kirill Tkhai wrote:
> Bad situation:
> double_lock_balance() drops busiest_rq lock. The busiest_rq is *busiest*,
> and a lot of tasks and context switches there. We are dropping the lock
> and waiting for it again.
> Let's just detach the task and once finally unlock it!
> Warning: this admits unlocked using of can_migrate_task(), throttled_lb_pair(),
> and task_hot(). I added comments about that.

Wonder if we should also consider removing double_lock_balance usage
from rt.c and deadline.c? Then those two schedulers will also not
lock both the source and destination queues at the same time
for load balancing.


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