Kirill Tkhai <[email protected]> writes: > 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.
I mean, you need get_online_cpus anyway - cpu_online is just a test against the same mask that for_each_online_cpu uses, and without taking the lock you can still race with offlining and reset runtime_enabled. -- 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/
