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

  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
 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@bytedance.com>
---
 kernel/sched/core.c | 11 +++++++----
 kernel/sched/fair.c |  9 ++++++---
 2 files changed, 13 insertions(+), 7 deletions(-)
  

On Mon, 10 Apr 2023 at 10:12, Hao Jia <jiahao.os@bytedance.com> 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@bytedance.com>
> ---
>  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
>
  

On 2023/4/21 Vincent Guittot wrote:
> On Mon, 10 Apr 2023 at 10:12, Hao Jia <jiahao.os@bytedance.com> 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 ?

Sorry for the late reply, I just got back from a long term.

IIRC, this is not generated by patch1.

In the unthrottle_offline_cfs_rqs() function, we traverse task_groups 
through list_for_each_entry_rcu, so unthrottle_cfs_rq() may be called 
multiple times, resulting in multiple updates to the rq clock.

Thanks,
Hao
> 
>>   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().
>>
  

Le mardi 02 mai 2023 à 18:22:56 (+0800), Hao Jia a écrit :
> 
> 
> On 2023/4/21 Vincent Guittot wrote:
> > On Mon, 10 Apr 2023 at 10:12, Hao Jia <jiahao.os@bytedance.com> 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 ?
> 
> Sorry for the late reply, I just got back from a long term.
> 
> IIRC, this is not generated by patch1.

yeah, that's in the cfs loop

> 
> In the unthrottle_offline_cfs_rqs() function, we traverse task_groups
> through list_for_each_entry_rcu, so unthrottle_cfs_rq() may be called
> multiple times, resulting in multiple updates to the rq clock.
> 
> Thanks,
> Hao
> > 
> > >   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().

Can we do the opposite ?
AFAICT, update_rq_clock() in __balance_push_cpu_stop() is only there for
__migrate_task(). I prefer to keep the update_rq_clock() as close as possible
to the user

> > > 
> > > 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

This happens with the for loop added by
commit: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")

> > > in order to avoid missing rq clock update, we correspondingly add
> > > update_rq_clock() calls before unthrottle_cfs_rq() runs.

These are special cases that happen because of the for_each.
As said above, I would prefer keeping update_rq_clock close the their user

could we use something similar to rq_clock_skip_update() for those list ?

Something like the below:

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 898fa3bc2765..7495b6fb229d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9386,8 +9386,6 @@ static int __balance_push_cpu_stop(void *arg)
        raw_spin_lock_irq(&p->pi_lock);
        rq_lock(rq, &rf);

-       update_rq_clock(rq);
-
        if (task_rq(p) == rq && task_on_rq_queued(p)) {
                cpu = select_fallback_rq(rq->cpu, p);
                rq = __migrate_task(rq, &rf, p, cpu);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 503b7617d7e1..a1d47d907360 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5518,6 +5518,12 @@ static void __cfsb_csd_unthrottle(void *arg)
        struct rq_flags rf;

        rq_lock(rq, &rf);
+       /*
+        * Iterating over the list can trigger several call to update_rq_clock.
+        * Do it once and skip the potential next ones.
+        */
+       update_rq_clock(rq);
+       rq_clock_loop_update(rq);

        /*
         * Since we hold rq lock we're safe from concurrent manipulation of
@@ -6058,6 +6064,13 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)

        lockdep_assert_rq_held(rq);

+       /*
+        * Iterating over the list can trigger several call to update_rq_clock.
+        * Do it once and skip the potential next ones.
+        */
+       update_rq_clock(rq);
+       rq_clock_loop_update(rq);
+
        rcu_read_lock();
        list_for_each_entry_rcu(tg, &task_groups, list) {
                struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 66bacd50d381..681924367891 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1536,6 +1536,19 @@ static inline void rq_clock_skip_update(struct rq *rq)
        rq->clock_update_flags |= RQCF_REQ_SKIP;
 }

+/*
+ * During cpu offlining and rq wide unthrottling, we can trigger
+ * an update_rq_clock() for several cfs and rt runqueues (Typically
+ * when using list_for_each_entry_*)
+ * rq_clock_loop_update() can be called after updating the clock once
+ * and before iterating over the list to prevent multiple update.
+ */
+static inline void rq_clock_loop_update(struct rq *rq)
+{
+       lockdep_assert_rq_held(rq);
+       rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
 /*
  * See rt task throttling, which is the only time a skip
  * request is canceled.


> > > 
> > > 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().
> > > 
> 
> 
>
  

On 2023/5/5 Vincent Guittot wrote:

>>>>    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().
> 
> Can we do the opposite ?
> AFAICT, update_rq_clock() in __balance_push_cpu_stop() is only there for
> __migrate_task(). I prefer to keep the update_rq_clock() as close as possible
> to the user

I'm afraid not, the rq clock also needs to be updated before 
select_fallback_rq() is called.


> 
>>>>
>>>> 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
> 
> This happens with the for loop added by
> commit: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
> 

Yes, the warning caused by this commit.

>>>> in order to avoid missing rq clock update, we correspondingly add
>>>> update_rq_clock() calls before unthrottle_cfs_rq() runs.
> 
> These are special cases that happen because of the for_each.
> As said above, I would prefer keeping update_rq_clock close the their user
> 
> could we use something similar to rq_clock_skip_update() for those list ?
> 

I try to do it with the method you provided. Some things maybe like this?

We also need to clear RQCF_ACT_SKIP after calling rq_clock_loop_update() 
to avoid some warnings.


diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index efdab1489113..f48b5d912d8c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2420,7 +2420,6 @@ 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;
@@ -2478,10 +2477,12 @@ 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
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 373ff5f55884..1dcef273bebe 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5575,6 +5575,13 @@ static void __cfsb_csd_unthrottle(void *arg)
         struct rq_flags rf;

         rq_lock(rq, &rf);
+       /*
+        * Iterating over the list can trigger several call to 
update_rq_clock()
+        * in unthrottle_cfs_rq().
+        * Do it once and skip the potential next ones.
+        */
+       update_rq_clock(rq);
+       rq_clock_loop_update(rq);

         /*
          * Since we hold rq lock we're safe from concurrent manipulation of
@@ -5595,6 +5602,7 @@ static void __cfsb_csd_unthrottle(void *arg)

         rcu_read_unlock();

+       rq_clock_cancel_loop_update(rq);
         rq_unlock(rq, &rf);
  }

@@ -6114,6 +6122,12 @@ static void __maybe_unused 
unthrottle_offline_cfs_rqs(struct rq *rq)
         struct task_group *tg;

         lockdep_assert_rq_held(rq);
+       /*
+        * The rq clock has already been updated before the
+        * set_rq_offline() runs, so we should skip updating
+        * the rq clock again in unthrottle_cfs_rq().
+        */
+       rq_clock_loop_update(rq);

         rcu_read_lock();
         list_for_each_entry_rcu(tg, &task_groups, list) {
@@ -6137,6 +6151,7 @@ static void __maybe_unused 
unthrottle_offline_cfs_rqs(struct rq *rq)
                         unthrottle_cfs_rq(cfs_rq);
         }
         rcu_read_unlock();
+       rq_clock_cancel_loop_update(rq);
  }

  #else /* CONFIG_CFS_BANDWIDTH */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec7b3e0a2b20..3d4981d354a9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1536,6 +1536,25 @@ static inline void rq_clock_skip_update(struct rq 
*rq)
         rq->clock_update_flags |= RQCF_REQ_SKIP;
  }

+/*
+ * During cpu offlining and rq wide unthrottling, we can trigger
+ * an update_rq_clock() for several cfs and rt runqueues (Typically
+ * when using list_for_each_entry_*)
+ * rq_clock_loop_update() can be called after updating the clock once
+ * and before iterating over the list to prevent multiple update.
+ */
+static inline void rq_clock_loop_update(struct rq *rq)
+{
+       lockdep_assert_rq_held(rq);
+       rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
+static inline void rq_clock_cancel_loop_update(struct rq *rq)
+{
+       lockdep_assert_rq_held(rq);
+       rq->clock_update_flags &= ~RQCF_ACT_SKIP;
+}
+
  /*
   * See rt task throttling, which is the only time a skip
  

On Fri, 5 May 2023 at 14:13, Hao Jia <jiahao.os@bytedance.com> wrote:
>
>
>
> On 2023/5/5 Vincent Guittot wrote:
>
> >>>>    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().
> >
> > Can we do the opposite ?
> > AFAICT, update_rq_clock() in __balance_push_cpu_stop() is only there for
> > __migrate_task(). I prefer to keep the update_rq_clock() as close as possible
> > to the user
>
> I'm afraid not, the rq clock also needs to be updated before
> select_fallback_rq() is called.

yes you're right

>
>
> >
> >>>>
> >>>> 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
> >
> > This happens with the for loop added by
> > commit: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
> >
>
> Yes, the warning caused by this commit.
>
> >>>> in order to avoid missing rq clock update, we correspondingly add
> >>>> update_rq_clock() calls before unthrottle_cfs_rq() runs.
> >
> > These are special cases that happen because of the for_each.
> > As said above, I would prefer keeping update_rq_clock close the their user
> >
> > could we use something similar to rq_clock_skip_update() for those list ?
> >
>
> I try to do it with the method you provided. Some things maybe like this?
>
> We also need to clear RQCF_ACT_SKIP after calling rq_clock_loop_update()
> to avoid some warnings.
>
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index efdab1489113..f48b5d912d8c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2420,7 +2420,6 @@ 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;
> @@ -2478,10 +2477,12 @@ 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
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 373ff5f55884..1dcef273bebe 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5575,6 +5575,13 @@ static void __cfsb_csd_unthrottle(void *arg)
>          struct rq_flags rf;
>
>          rq_lock(rq, &rf);
> +       /*
> +        * Iterating over the list can trigger several call to
> update_rq_clock()
> +        * in unthrottle_cfs_rq().
> +        * Do it once and skip the potential next ones.
> +        */
> +       update_rq_clock(rq);
> +       rq_clock_loop_update(rq);
>
>          /*
>           * Since we hold rq lock we're safe from concurrent manipulation of
> @@ -5595,6 +5602,7 @@ static void __cfsb_csd_unthrottle(void *arg)
>
>          rcu_read_unlock();
>
> +       rq_clock_cancel_loop_update(rq);
>          rq_unlock(rq, &rf);
>   }
>
> @@ -6114,6 +6122,12 @@ static void __maybe_unused
> unthrottle_offline_cfs_rqs(struct rq *rq)
>          struct task_group *tg;
>
>          lockdep_assert_rq_held(rq);
> +       /*
> +        * The rq clock has already been updated before the
> +        * set_rq_offline() runs, so we should skip updating
> +        * the rq clock again in unthrottle_cfs_rq().
> +        */
> +       rq_clock_loop_update(rq);
>
>          rcu_read_lock();
>          list_for_each_entry_rcu(tg, &task_groups, list) {
> @@ -6137,6 +6151,7 @@ static void __maybe_unused
> unthrottle_offline_cfs_rqs(struct rq *rq)
>                          unthrottle_cfs_rq(cfs_rq);
>          }
>          rcu_read_unlock();
> +       rq_clock_cancel_loop_update(rq);
>   }
>
>   #else /* CONFIG_CFS_BANDWIDTH */
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index ec7b3e0a2b20..3d4981d354a9 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1536,6 +1536,25 @@ static inline void rq_clock_skip_update(struct rq
> *rq)
>          rq->clock_update_flags |= RQCF_REQ_SKIP;
>   }
>
> +/*
> + * During cpu offlining and rq wide unthrottling, we can trigger
> + * an update_rq_clock() for several cfs and rt runqueues (Typically
> + * when using list_for_each_entry_*)
> + * rq_clock_loop_update() can be called after updating the clock once
> + * and before iterating over the list to prevent multiple update.
> + */
> +static inline void rq_clock_loop_update(struct rq *rq)

maybe use rq_clock_start_loop_update

> +{
> +       lockdep_assert_rq_held(rq);
> +       rq->clock_update_flags |= RQCF_ACT_SKIP;
> +}
> +
> +static inline void rq_clock_cancel_loop_update(struct rq *rq)

and rq_clock_stop_loop_update here

> +{
> +       lockdep_assert_rq_held(rq);
> +       rq->clock_update_flags &= ~RQCF_ACT_SKIP;
> +}
> +
>   /*
>    * See rt task throttling, which is the only time a skip