Re: [PATCH 2/2] sched/core: Avoid double calling update_rq_clock()

[Vincent Guittot]

On Mon, 10 Apr 2023 at 10:12, Hao Jia <jiahao.os@xxxxxxxxxxxxx> wrote:
>
> There are some double rq clock update warnings are triggered.
> ------------[ cut here ]------------
> rq->clock_update_flags & RQCF_UPDATED
> WARNING: CPU: 17 PID: 138 at kernel/sched/core.c:741
> update_rq_clock+0xaf/0x180
> Call Trace:
>  <TASK>
>  __balance_push_cpu_stop+0x146/0x180
>  ? migration_cpu_stop+0x2a0/0x2a0
>  cpu_stopper_thread+0xa3/0x140
>  smpboot_thread_fn+0x14f/0x210
>  ? sort_range+0x20/0x20
>  kthread+0xe6/0x110
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x1f/0x30
>
> ------------[ cut here ]------------
> rq->clock_update_flags & RQCF_UPDATED
> WARNING: CPU: 54 PID: 0 at kernel/sched/core.c:741
> update_rq_clock+0xaf/0x180
> Call Trace:
>  <TASK>
>  unthrottle_cfs_rq+0x4b/0x300
>  __cfsb_csd_unthrottle+0xe0/0x100
>  __flush_smp_call_function_queue+0xaf/0x1d0
>  flush_smp_call_function_queue+0x49/0x90
>  do_idle+0x17c/0x270
>  cpu_startup_entry+0x19/0x20
>  start_secondary+0xfa/0x120
>  secondary_startup_64_no_verify+0xce/0xdb
>
> ------------[ cut here ]------------
> rq->clock_update_flags & RQCF_UPDATED
> WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
> update_rq_clock+0xaf/0x180
> Call Trace:
>  <TASK>
>  unthrottle_cfs_rq+0x4b/0x300
>  rq_offline_fair+0x89/0x90
>  set_rq_offline.part.118+0x28/0x60

So this is generated by patch 1, isn't it ?

>  rq_attach_root+0xc4/0xd0
>  cpu_attach_domain+0x3dc/0x7f0
>  partition_sched_domains_locked+0x2a5/0x3c0
>  rebuild_sched_domains_locked+0x477/0x830
>  rebuild_sched_domains+0x1b/0x30
>  cpuset_hotplug_workfn+0x2ca/0xc90
>  ? balance_push+0x56/0xf0
>  ? _raw_spin_unlock+0x15/0x30
>  ? finish_task_switch+0x98/0x2f0
>  ? __switch_to+0x291/0x410
>  ? __schedule+0x65e/0x1310
>  process_one_work+0x1bc/0x3d0
>  worker_thread+0x4c/0x380
>  ? preempt_count_add+0x92/0xa0
>  ? rescuer_thread+0x310/0x310
>  kthread+0xe6/0x110
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x1f/0x30
>
> For the __balance_push_cpu_stop() case, we remove update_rq_clock() from
> the __migrate_task() function to avoid double updating the rq clock.
> And in order to avoid missing rq clock update, add update_rq_clock()
> call before migration_cpu_stop() calls __migrate_task().
>
> This also works for unthrottle_cfs_rq(), so we also removed
> update_rq_clock() from the unthrottle_cfs_rq() function to avoid
> warnings caused by calling it multiple times, such as
> __cfsb_csd_unthrottle() and unthrottle_offline_cfs_rqs(). and
> in order to avoid missing rq clock update, we correspondingly add
> update_rq_clock() calls before unthrottle_cfs_rq() runs.
>
> Note that the rq clock has been updated before the set_rq_offline()
> function runs, so we don't need to add update_rq_clock() call in
> unthrottle_offline_cfs_rqs().
>
> Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
> ---
>  kernel/sched/core.c | 11 +++++++----
>  kernel/sched/fair.c |  9 ++++++---
>  2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0d18c3969f90..c1abd88ec1ed 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2376,7 +2376,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
>         if (!is_cpu_allowed(p, dest_cpu))
>                 return rq;
>
> -       update_rq_clock(rq);
>         rq = move_queued_task(rq, rf, p, dest_cpu);
>
>         return rq;
> @@ -2434,10 +2433,12 @@ static int migration_cpu_stop(void *data)
>                                 goto out;
>                 }
>
> -               if (task_on_rq_queued(p))
> +               if (task_on_rq_queued(p)) {
> +                       update_rq_clock(rq);
>                         rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
> -               else
> +               } else {
>                         p->wake_cpu = arg->dest_cpu;
> +               }
>
>                 /*
>                  * XXX __migrate_task() can fail, at which point we might end
> @@ -10759,8 +10760,10 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
>                 cfs_rq->runtime_enabled = runtime_enabled;
>                 cfs_rq->runtime_remaining = 0;
>
> -               if (cfs_rq->throttled)
> +               if (cfs_rq->throttled) {
> +                       update_rq_clock(rq);
>                         unthrottle_cfs_rq(cfs_rq);
> +               }
>                 rq_unlock_irq(rq, &rf);
>         }
>         if (runtime_was_enabled && !runtime_enabled)
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6986ea31c984..03ced34e992e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5438,8 +5438,6 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>
>         cfs_rq->throttled = 0;
>
> -       update_rq_clock(rq);
> -
>         raw_spin_lock(&cfs_b->lock);
>         cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
>         list_del_rcu(&cfs_rq->throttled_list);
> @@ -5518,6 +5516,7 @@ static void __cfsb_csd_unthrottle(void *arg)
>         struct rq_flags rf;
>
>         rq_lock(rq, &rf);
> +       update_rq_clock(rq);
>
>         /*
>          * Since we hold rq lock we're safe from concurrent manipulation of
> @@ -5547,6 +5546,7 @@ static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
>         bool first;
>
>         if (rq == this_rq()) {
> +               update_rq_clock(rq);
>                 unthrottle_cfs_rq(cfs_rq);
>                 return;
>         }
> @@ -5563,6 +5563,7 @@ static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
>  #else
>  static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
>  {
> +       update_rq_clock(rq_of(cfs_rq));
>         unthrottle_cfs_rq(cfs_rq);
>  }
>  #endif
> @@ -5640,8 +5641,10 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
>         if (local_unthrottle) {
>                 rq = cpu_rq(this_cpu);
>                 rq_lock_irqsave(rq, &rf);
> -               if (cfs_rq_throttled(local_unthrottle))
> +               if (cfs_rq_throttled(local_unthrottle)) {
> +                       update_rq_clock(rq);
>                         unthrottle_cfs_rq(local_unthrottle);
> +               }
>                 rq_unlock_irqrestore(rq, &rf);
>         }
>
> --
> 2.37.0
>