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author | Peter Zijlstra <peterz@infradead.org> | 2021-01-21 18:09:32 +0300 |
---|---|---|
committer | Peter Zijlstra <peterz@infradead.org> | 2021-04-16 18:06:32 +0300 |
commit | b5c4477366fb5e6a2f0f38742c33acd666c07698 (patch) | |
tree | bd7fa4cb0d72be06c611009cd76d94ce85142eeb | |
parent | e40f74c535b8a0ecf3ef0388b51a34cdadb34fb5 (diff) | |
download | linux-b5c4477366fb5e6a2f0f38742c33acd666c07698.tar.xz |
sched: Use cpu_dying() to fix balance_push vs hotplug-rollback
Use the new cpu_dying() state to simplify and fix the balance_push()
vs CPU hotplug rollback state.
Specifically, we currently rely on notifiers sched_cpu_dying() /
sched_cpu_activate() to terminate balance_push, however if the
cpu_down() fails when we're past sched_cpu_deactivate(), it should
terminate balance_push at that point and not wait until we hit
sched_cpu_activate().
Similarly, when cpu_up() fails and we're going back down, balance_push
should be active, where it currently is not.
So instead, make sure balance_push is enabled below SCHED_AP_ACTIVE
(when !cpu_active()), and gate it's utility with cpu_dying().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/YHgAYef83VQhKdC2@hirez.programming.kicks-ass.net
-rw-r--r-- | kernel/sched/core.c | 26 | ||||
-rw-r--r-- | kernel/sched/sched.h | 1 |
2 files changed, 15 insertions, 12 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 95bd6ab8115d..7d031da20df3 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1811,7 +1811,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) return cpu_online(cpu); /* Regular kernel threads don't get to stay during offline. */ - if (cpu_rq(cpu)->balance_push) + if (cpu_dying(cpu)) return false; /* But are allowed during online. */ @@ -7638,6 +7638,9 @@ static DEFINE_PER_CPU(struct cpu_stop_work, push_work); /* * Ensure we only run per-cpu kthreads once the CPU goes !active. + * + * This is enabled below SCHED_AP_ACTIVE; when !cpu_active(), but only + * effective when the hotplug motion is down. */ static void balance_push(struct rq *rq) { @@ -7645,12 +7648,19 @@ static void balance_push(struct rq *rq) lockdep_assert_held(&rq->lock); SCHED_WARN_ON(rq->cpu != smp_processor_id()); + /* * Ensure the thing is persistent until balance_push_set(.on = false); */ rq->balance_callback = &balance_push_callback; /* + * Only active while going offline. + */ + if (!cpu_dying(rq->cpu)) + return; + + /* * Both the cpu-hotplug and stop task are in this case and are * required to complete the hotplug process. * @@ -7703,7 +7713,6 @@ static void balance_push_set(int cpu, bool on) struct rq_flags rf; rq_lock_irqsave(rq, &rf); - rq->balance_push = on; if (on) { WARN_ON_ONCE(rq->balance_callback); rq->balance_callback = &balance_push_callback; @@ -7828,8 +7837,8 @@ int sched_cpu_activate(unsigned int cpu) struct rq_flags rf; /* - * Make sure that when the hotplug state machine does a roll-back - * we clear balance_push. Ideally that would happen earlier... + * Clear the balance_push callback and prepare to schedule + * regular tasks. */ balance_push_set(cpu, false); @@ -8014,12 +8023,6 @@ int sched_cpu_dying(unsigned int cpu) } rq_unlock_irqrestore(rq, &rf); - /* - * Now that the CPU is offline, make sure we're welcome - * to new tasks once we come back up. - */ - balance_push_set(cpu, false); - calc_load_migrate(rq); update_max_interval(); hrtick_clear(rq); @@ -8204,7 +8207,7 @@ void __init sched_init(void) rq->sd = NULL; rq->rd = NULL; rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE; - rq->balance_callback = NULL; + rq->balance_callback = &balance_push_callback; rq->active_balance = 0; rq->next_balance = jiffies; rq->push_cpu = 0; @@ -8251,6 +8254,7 @@ void __init sched_init(void) #ifdef CONFIG_SMP idle_thread_set_boot_cpu(); + balance_push_set(smp_processor_id(), false); #endif init_sched_fair_class(); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index cbb0b011e9e0..7e7e936b4938 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -983,7 +983,6 @@ struct rq { unsigned long cpu_capacity_orig; struct callback_head *balance_callback; - unsigned char balance_push; unsigned char nohz_idle_balance; unsigned char idle_balance; |