Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/2] sched: Rework migrate_tasks() | From | Kirill Tkhai <> | Date | Wed, 11 Jun 2014 23:33:14 +0400 |
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В Ср, 11/06/2014 в 17:43 +0400, Kirill Tkhai пишет: > > 11.06.2014, 17:15, "Srikar Dronamraju" <srikar@linux.vnet.ibm.com>: > >>> * Kirill Tkhai <ktkhai@parallels.com> [2014-06-11 13:52:10]: > >>>> Currently migrate_tasks() skips throttled tasks, > >>>> because they are not pickable by pick_next_task(). > >>> Before migrate_tasks() is called, we do call set_rq_offline(), in > >>> migration_call(). > >>> > >>> Shouldnt this take care of unthrottling the tasks and making sure that > >>> they can be picked by pick_next_task(). > >> If we do this separate for every class, we'll have to do this 3 times. > >> Furthermore, deadline class does not have a list of throttled tasks. > >> So we'll have to the same as I did: to lock tasklist_lock and to iterate > >> throw all of the tasks in the system just to found deadline tasks. > > > > I think you misread my comment. > > > > Currently migrate_task() gets called from migration_call() and in the > > migration_call() before migrate_tasks(), set_rq_offline() should put > > tasks back using unthrottle_cfs_rq(). > > > > So my question is: Why are these tasks not getting unthrottled > > through we are calling set_rq_offline? To me set_rq_offline is > > calling the actual sched class routines to do the needful. > > > > I can understand about deadline tasks, because we don't have a deadline > > But thats the only tasks that we need to fix. > > Hm, I tested that on fair class tasks. They used to disappear from > /proc/sched_debug and used to hang. I'll check all once again. > > I'm agree with you, if set_rq_offline() already presents, we should use it. > > /me went to clarify why it does not work in my test.
Ok, it looks like the problem is that unthrottled cfs_rq may become throttled again ;)
__migrate_task()->dequeue_task() calls update_rq_clock(), which throttles just unthrottle cfs_rq after a first picked task is moved.
Hope, something like above helps, I'll check if there are no other problem and write again.
--- kernel/sched/core.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d0d1565..b5fd6f0 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4843,6 +4843,12 @@ static void migrate_tasks(unsigned int dead_cpu) */ update_rq_clock(rq); + /* + * Prevent rq->clock update from __migrate_task()->dequeue_task() + * to do not throttle sched_class queues and tasks. + */ + rq->skip_clock_update = 1; + for ( ; ; ) { /* * There's this thread running, bail when that's the only @@ -4864,6 +4870,8 @@ static void migrate_tasks(unsigned int dead_cpu) raw_spin_lock(&rq->lock); } + rq->skip_clock_update = 0; /* Reset it back */ + rq->stop = stop; }
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