Kirill Tkhai <ktk...@parallels.com> 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 <ktk...@parallels.com>
> CC: Konstantin Khorenko <khore...@parallels.com>
> CC: Ben Segall <bseg...@google.com>
> CC: Paul Turner <p...@google.com>
> CC: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> CC: Mike Galbraith <umgwanakikb...@gmail.com>
> CC: Peter Zijlstra <pet...@infradead.org>
> CC: Ingo Molnar <mi...@kernel.org>
> ---
> 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?
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