[v2,2/2] sched/core: Avoid double calling update_rq_clock()
Commit Message
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().
For the unthrottle_cfs_rq() case, we use rq_clock_start_loop_update() to
prevent multiple calls to update_rq_clock() in unthrottle_cfs_rq().
Note that the rq clock has been updated before the set_rq_offline()
function runs, so we don't need to call update_rq_clock() in
unthrottle_offline_cfs_rqs().
Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
---
kernel/sched/core.c | 7 ++++---
kernel/sched/fair.c | 16 ++++++++++++++++
kernel/sched/sched.h | 21 +++++++++++++++++++++
3 files changed, 41 insertions(+), 3 deletions(-)
Comments
On Wed, May 10, 2023 at 04:34:50PM +0800, Hao Jia 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
> 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().
>
> For the unthrottle_cfs_rq() case, we use rq_clock_start_loop_update() to
> prevent multiple calls to update_rq_clock() in unthrottle_cfs_rq().
>
> Note that the rq clock has been updated before the set_rq_offline()
> function runs, so we don't need to call update_rq_clock() in
> unthrottle_offline_cfs_rqs().
This reads like 3 separate issues -- in which case this ought to be 3
separate patches.
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index ec7b3e0a2b20..9c712f29e5a4 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1536,6 +1536,27 @@ 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_start_loop_update() can be called after updating the clock
> + * once and before iterating over the list to prevent multiple update.
> + * After the iterative traversal, we need to call rq_clock_stop_loop_update()
> + * to restore rq->clock_update_flags.
^^^^^^^
> + */
> +static inline void rq_clock_start_loop_update(struct rq *rq)
> +{
> + lockdep_assert_rq_held(rq);
> + rq->clock_update_flags |= RQCF_ACT_SKIP;
> +}
> +
> +static inline void rq_clock_stop_loop_update(struct rq *rq)
> +{
> + lockdep_assert_rq_held(rq);
> + rq->clock_update_flags &= ~RQCF_ACT_SKIP;
> +}
This does not restore the flag, it clears the flag.
On 2023/5/10 Peter Zijlstra wrote:
> On Wed, May 10, 2023 at 04:34:50PM +0800, Hao Jia wrote:
>> 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().
>>
>> For the unthrottle_cfs_rq() case, we use rq_clock_start_loop_update() to
>> prevent multiple calls to update_rq_clock() in unthrottle_cfs_rq().
>>
>> Note that the rq clock has been updated before the set_rq_offline()
>> function runs, so we don't need to call update_rq_clock() in
>> unthrottle_offline_cfs_rqs().
>
> This reads like 3 separate issues -- in which case this ought to be 3
> separate patches.
I will do it in the next version.
Thanks,
Hao
>
>
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index ec7b3e0a2b20..9c712f29e5a4 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -1536,6 +1536,27 @@ 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_start_loop_update() can be called after updating the clock
>> + * once and before iterating over the list to prevent multiple update.
>> + * After the iterative traversal, we need to call rq_clock_stop_loop_update()
>> + * to restore rq->clock_update_flags.
> ^^^^^^^
>> + */
>> +static inline void rq_clock_start_loop_update(struct rq *rq)
>> +{
>> + lockdep_assert_rq_held(rq);
>> + rq->clock_update_flags |= RQCF_ACT_SKIP;
>> +}
>> +
>> +static inline void rq_clock_stop_loop_update(struct rq *rq)
>> +{
>> + lockdep_assert_rq_held(rq);
>> + rq->clock_update_flags &= ~RQCF_ACT_SKIP;
>> +}
>
> This does not restore the flag, it clears the flag.
Thanks for your review.
I will also modify it in the next version.
Thanks,
Hao
@@ -2398,7 +2398,6 @@ 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;
@@ -2456,10 +2455,12 @@ 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
@@ -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_start_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_stop_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_start_loop_update(rq);
rcu_read_lock();
list_for_each_entry_rcu(tg, &task_groups, list) {
@@ -6137,6 +6151,8 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
unthrottle_cfs_rq(cfs_rq);
}
rcu_read_unlock();
+
+ rq_clock_stop_loop_update(rq);
}
#else /* CONFIG_CFS_BANDWIDTH */
@@ -1536,6 +1536,27 @@ 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_start_loop_update() can be called after updating the clock
+ * once and before iterating over the list to prevent multiple update.
+ * After the iterative traversal, we need to call rq_clock_stop_loop_update()
+ * to restore rq->clock_update_flags.
+ */
+static inline void rq_clock_start_loop_update(struct rq *rq)
+{
+ lockdep_assert_rq_held(rq);
+ rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
+static inline void rq_clock_stop_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.