On 24.06.2014 21:03, [email protected] wrote: > Kirill Tkhai <[email protected]> writes: > >> We kill rq->rd on the CPU_DOWN_PREPARE stage: >> >> cpuset_cpu_inactive -> cpuset_update_active_cpus -> >> partition_sched_domains -> >> -> cpu_attach_domain -> rq_attach_root -> set_rq_offline >> >> This unthrottles all throttled cfs_rqs. >> >> But the cpu is still able to call schedule() till >> >> take_cpu_down->__cpu_disable() >> >> is called from stop_machine. >> >> This case the tasks from just unthrottled cfs_rqs are pickable >> in a standard scheduler way, and they are picked by dying cpu. >> The cfs_rqs becomes throttled again, and migrate_tasks() >> in migration_call skips their tasks (one more unthrottle >> in migrate_tasks()->CPU_DYING does not happen, because rq->rd >> is already NULL). >> >> Patch sets runtime_enabled to zero. This guarantees, the runtime >> is not accounted, and the cfs_rqs won't exceed given >> cfs_rq->runtime_remaining = 1, and tasks will be pickable >> in migrate_tasks(). runtime_enabled is recalculated again >> when rq becomes online again. >> >> Ben Segall also noticed, we always enable runtime in >> tg_set_cfs_bandwidth(). Actually, we should do that for online >> cpus only. To fix that, we check if a cpu is online when >> its rq is locked. This guarantees we do not have races with >> set_rq_offline(), which also requires rq->lock. >> >> v2: Fix race with tg_set_cfs_bandwidth(). >> Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq(). >> >> Signed-off-by: Kirill Tkhai <[email protected]> >> CC: Konstantin Khorenko <[email protected]> >> CC: Ben Segall <[email protected]> >> CC: Paul Turner <[email protected]> >> CC: Srikar Dronamraju <[email protected]> >> CC: Mike Galbraith <[email protected]> >> CC: Peter Zijlstra <[email protected]> >> CC: Ingo Molnar <[email protected]> >> --- >> kernel/sched/core.c | 15 +++++++++++---- >> kernel/sched/fair.c | 22 ++++++++++++++++++++++ >> 2 files changed, 33 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 7f3063c..707a3c5 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -7842,11 +7842,18 @@ static int tg_set_cfs_bandwidth(struct task_group >> *tg, u64 period, u64 quota) >> struct rq *rq = cfs_rq->rq; >> >> raw_spin_lock_irq(&rq->lock); >> - cfs_rq->runtime_enabled = runtime_enabled; >> - cfs_rq->runtime_remaining = 0; >> + /* >> + * Do not enable runtime on offline runqueues. We specially >> + * make it disabled in unthrottle_offline_cfs_rqs(). >> + */ >> + if (cpu_online(i)) { >> + cfs_rq->runtime_enabled = runtime_enabled; >> + cfs_rq->runtime_remaining = 0; >> + >> + if (cfs_rq->throttled) >> + unthrottle_cfs_rq(cfs_rq); >> + } > > We can just do for_each_online_cpu, yes? Also we probably need > get_online_cpus/put_online_cpus, and/or want cpu_active_mask instead > right? >
Yes, we can use for_each_online_cpu/for_each_active_cpu with get_online_cpus() taken. But it adds one more lock dependence. This looks worse for me. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
