These four patches fix some warnings about rq clock.
Patch1 fixes the warning of using the old rq clock caused by
missing update rq clock.
Patch2-4 fixes the warning that the rq clock was updated multiple
times while holding the rq lock.
v4->v5:
- Benjamin Segall suggested adding update_rq_clock() to set_rq_offline()
instead of calling update_rq_clock() before set_rq_offline() runs.
v3->v4:
- Add Reviewed-by: Vincent Guittot <[email protected]> for
all patches.
v2->v3:
- Modify the commit information of patch1 to make the description clearer.
- Split v2 patch2 into 3 separate patches.
v1->v2:
- Vincent Guittot suggested using rq_clock_start_loop_update()
to prevent multiple calls to update_rq_clock() in unthrottle_cfs_rq()
instead of removing update_rq_clock() from unthrottle_cfs_rq()
and updating the rq clock before unthrottle_cfs_rq() for patch2.
[v4] https://lore.kernel.org/all/[email protected]
[v3] https://lore.kernel.org/all/[email protected]
[v2] https://lore.kernel.org/all/[email protected]
[v1] https://lore.kernel.org/all/[email protected]
Hao Jia (4):
sched/core: Fixed missing rq clock update before calling
set_rq_offline()
sched/core: Avoid double calling update_rq_clock() in
__balance_push_cpu_stop()
sched/core: Avoid multiple calling update_rq_clock() in
__cfsb_csd_unthrottle()
sched/core: Avoid multiple calling update_rq_clock() in
unthrottle_offline_cfs_rqs()
kernel/sched/core.c | 9 +++++----
kernel/sched/fair.c | 18 ++++++++++++++++++
kernel/sched/sched.h | 21 +++++++++++++++++++++
kernel/sched/topology.c | 6 +++---
4 files changed, 47 insertions(+), 7 deletions(-)
--
2.20.1
The WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
------------[ 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
To avoid this warning, we remove update_rq_clock() from
the __migrate_task() function. And in order to avoid
missing rq clock update, add update_rq_clock() call before
migration_cpu_stop() calls __migrate_task().
Signed-off-by: Hao Jia <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
---
kernel/sched/core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a8be5415daba..1eca36299d8b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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
--
2.20.1
This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled
and cpufreq is set to powersave:
------------[ cut here ]------------
rq->clock_update_flags < RQCF_ACT_SKIP
WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
enqueue_top_rt_rq+0x139/0x160
Call Trace:
<TASK>
? intel_pstate_update_util+0x3b0/0x3b0
rq_offline_rt+0x1b7/0x250
set_rq_offline.part.120+0x28/0x60
rq_attach_root+0xc4/0xd0
cpu_attach_domain+0x3dc/0x7f0
? __schedule+0x65e/0x1310
partition_sched_domains_locked+0x2a5/0x3c0
rebuild_sched_domains_locked+0x477/0x830
? percpu_rwsem_wait+0x140/0x140
rebuild_sched_domains+0x1b/0x30
cpuset_hotplug_workfn+0x2ca/0xc90
? balance_push+0x56/0x120
? _raw_spin_unlock+0x15/0x30
? finish_task_switch+0x98/0x2f0
? __switch_to+0x116/0x410
? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
? _raw_spin_unlock_irqrestore+0x23/0x40
? add_timer_on+0xd5/0x130
process_one_work+0x1bc/0x3d0
worker_thread+0x4c/0x380
? preempt_count_add+0x56/0xa0
? rescuer_thread+0x310/0x310
kthread+0xe6/0x110
? kthread_complete_and_exit+0x20/0x20
ret_from_fork+0x1f/0x30
More detailed key function call graph:
rq_offline_rt()
__disable_runtime()
sched_rt_rq_enqueue()
enqueue_top_rt_rq()
cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
data->func(data, *rq_clock(rq)*, flags)
intel_pstate_update_util() <-- powersave policy callback function
Before calling rq_offline_rt() we need to update the rq clock to avoid
using the old rq clock, So we add update_rq_clock() to set_rq_offline()
to update rq clock. And we use rq_lock_irqsave()/rq_unlock_irqrestore()
to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore()
in rq_attach_root() to ensure that rq->clock_update_flags are cleared
before updating the rq clock.
Steps to reproduce:
1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
3. cpupower -c all frequency-set -g powersave
4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
system with n CPUs)
5. Offline cpu one by one until the warninng is triggered
Suggested-by: Ben Segall <[email protected]>
Signed-off-by: Hao Jia <[email protected]>
---
kernel/sched/core.c | 2 +-
kernel/sched/topology.c | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a68d1276bab0..a8be5415daba 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9548,6 +9548,7 @@ void set_rq_offline(struct rq *rq)
if (rq->online) {
const struct sched_class *class;
+ update_rq_clock(rq);
for_each_class(class) {
if (class->rq_offline)
class->rq_offline(rq);
@@ -9689,7 +9690,6 @@ int sched_cpu_deactivate(unsigned int cpu)
rq_lock_irqsave(rq, &rf);
if (rq->rd) {
- update_rq_clock(rq);
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
set_rq_offline(rq);
}
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6682535e37c8..52976eadfee9 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
void rq_attach_root(struct rq *rq, struct root_domain *rd)
{
struct root_domain *old_rd = NULL;
- unsigned long flags;
+ struct rq_flags rf;
- raw_spin_rq_lock_irqsave(rq, flags);
+ rq_lock_irqsave(rq, &rf);
if (rq->rd) {
old_rd = rq->rd;
@@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
set_rq_online(rq);
- raw_spin_rq_unlock_irqrestore(rq, flags);
+ rq_unlock_irqrestore(rq, &rf);
if (old_rd)
call_rcu(&old_rd->rcu, free_rootdomain);
--
2.20.1
After commit 8ad075c2eb1f ("sched: Async unthrottling for cfs
bandwidth"), we may update the rq clock multiple times in the loop of
__cfsb_csd_unthrottle(). At that time the following warning will be
triggered.
------------[ 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
Before the loop starts, we update the rq clock once and call
rq_clock_start_loop_update() to prevent updating the rq clock
multiple times. And call rq_clock_stop_loop_update() After
the loop to clear rq->clock_update_flags.
Fixes: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
Suggested-by: Vincent Guittot <[email protected]>
Signed-off-by: Hao Jia <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
---
kernel/sched/fair.c | 9 +++++++++
kernel/sched/sched.h | 21 +++++++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 373ff5f55884..af9604f4b135 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5576,6 +5576,14 @@ static void __cfsb_csd_unthrottle(void *arg)
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
* the CSD list. However, this RCU critical section annotates the
@@ -5595,6 +5603,7 @@ static void __cfsb_csd_unthrottle(void *arg)
rcu_read_unlock();
+ rq_clock_stop_loop_update(rq);
rq_unlock(rq, &rf);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec7b3e0a2b20..50446e401b9f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1546,6 +1546,27 @@ static inline void rq_clock_cancel_skipupdate(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 clear RQCF_ACT_SKIP of 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;
+}
+
struct rq_flags {
unsigned long flags;
struct pin_cookie cookie;
--
2.20.1
On 2023/6/13 Hao Jia wrote:
> This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled
> and cpufreq is set to powersave:
> ------------[ cut here ]------------
> rq->clock_update_flags < RQCF_ACT_SKIP
> WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
> enqueue_top_rt_rq+0x139/0x160
> Call Trace:
> <TASK>
> ? intel_pstate_update_util+0x3b0/0x3b0
> rq_offline_rt+0x1b7/0x250
> set_rq_offline.part.120+0x28/0x60
> rq_attach_root+0xc4/0xd0
> cpu_attach_domain+0x3dc/0x7f0
> ? __schedule+0x65e/0x1310
> partition_sched_domains_locked+0x2a5/0x3c0
> rebuild_sched_domains_locked+0x477/0x830
> ? percpu_rwsem_wait+0x140/0x140
> rebuild_sched_domains+0x1b/0x30
> cpuset_hotplug_workfn+0x2ca/0xc90
> ? balance_push+0x56/0x120
> ? _raw_spin_unlock+0x15/0x30
> ? finish_task_switch+0x98/0x2f0
> ? __switch_to+0x116/0x410
> ? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
> ? _raw_spin_unlock_irqrestore+0x23/0x40
> ? add_timer_on+0xd5/0x130
> process_one_work+0x1bc/0x3d0
> worker_thread+0x4c/0x380
> ? preempt_count_add+0x56/0xa0
> ? rescuer_thread+0x310/0x310
> kthread+0xe6/0x110
> ? kthread_complete_and_exit+0x20/0x20
> ret_from_fork+0x1f/0x30
>
> More detailed key function call graph:
> rq_offline_rt()
> __disable_runtime()
> sched_rt_rq_enqueue()
> enqueue_top_rt_rq()
> cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
> data->func(data, *rq_clock(rq)*, flags)
> intel_pstate_update_util() <-- powersave policy callback function
>
> Before calling rq_offline_rt() we need to update the rq clock to avoid
> using the old rq clock, So we add update_rq_clock() to set_rq_offline()
> to update rq clock. And we use rq_lock_irqsave()/rq_unlock_irqrestore()
> to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore()
> in rq_attach_root() to ensure that rq->clock_update_flags are cleared
> before updating the rq clock.
>
> Steps to reproduce:
> 1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
> 2. echo 1 > /sys/kernel/debug/clear_warn_once
> 3. cpupower -c all frequency-set -g powersave
> 4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
> system with n CPUs)
> 5. Offline cpu one by one until the warninng is triggered
>
> Suggested-by: Ben Segall <[email protected]>
> Signed-off-by: Hao Jia <[email protected]>
Hi Vincent,
Benjamin Segall suggested adding update_rq_clock() to set_rq_offline()
instead of calling update_rq_clock() before set_rq_offline() runs.
The code of patch1 has changed, so I removed your tag "Reviewed-by".
Please review again.
Thanks,
Hao
> ---
> kernel/sched/core.c | 2 +-
> kernel/sched/topology.c | 6 +++---
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a68d1276bab0..a8be5415daba 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9548,6 +9548,7 @@ void set_rq_offline(struct rq *rq)
> if (rq->online) {
> const struct sched_class *class;
>
> + update_rq_clock(rq);
> for_each_class(class) {
> if (class->rq_offline)
> class->rq_offline(rq);
> @@ -9689,7 +9690,6 @@ int sched_cpu_deactivate(unsigned int cpu)
>
> rq_lock_irqsave(rq, &rf);
> if (rq->rd) {
> - update_rq_clock(rq);
> BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
> set_rq_offline(rq);
> }
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 6682535e37c8..52976eadfee9 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
> void rq_attach_root(struct rq *rq, struct root_domain *rd)
> {
> struct root_domain *old_rd = NULL;
> - unsigned long flags;
> + struct rq_flags rf;
>
> - raw_spin_rq_lock_irqsave(rq, flags);
> + rq_lock_irqsave(rq, &rf);
>
> if (rq->rd) {
> old_rd = rq->rd;
> @@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
> if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
> set_rq_online(rq);
>
> - raw_spin_rq_unlock_irqrestore(rq, flags);
> + rq_unlock_irqrestore(rq, &rf);
>
> if (old_rd)
> call_rcu(&old_rd->rcu, free_rootdomain);
This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
------------[ 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
The rq clock has been updated in the set_rq_offline(),
so we don't need to call update_rq_clock() in
unthrottle_offline_cfs_rqs().
We only need to call rq_clock_start_loop_update() before the
loop starts and rq_clock_stop_loop_update() after the loop
to avoid this warning.
Suggested-by: Vincent Guittot <[email protected]>
Signed-off-by: Hao Jia <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
---
kernel/sched/fair.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af9604f4b135..4da5f3541762 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6124,6 +6124,13 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
lockdep_assert_rq_held(rq);
+ /*
+ * The rq clock has already been updated in the
+ * set_rq_offline(), 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) {
struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
@@ -6146,6 +6153,8 @@ 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 */
--
2.20.1
On Tue, 13 Jun 2023 at 10:31, Hao Jia <[email protected]> wrote:
>
>
>
> On 2023/6/13 Hao Jia wrote:
> > This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled
> > and cpufreq is set to powersave:
> > ------------[ cut here ]------------
> > rq->clock_update_flags < RQCF_ACT_SKIP
> > WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
> > enqueue_top_rt_rq+0x139/0x160
> > Call Trace:
> > <TASK>
> > ? intel_pstate_update_util+0x3b0/0x3b0
> > rq_offline_rt+0x1b7/0x250
> > set_rq_offline.part.120+0x28/0x60
> > rq_attach_root+0xc4/0xd0
> > cpu_attach_domain+0x3dc/0x7f0
> > ? __schedule+0x65e/0x1310
> > partition_sched_domains_locked+0x2a5/0x3c0
> > rebuild_sched_domains_locked+0x477/0x830
> > ? percpu_rwsem_wait+0x140/0x140
> > rebuild_sched_domains+0x1b/0x30
> > cpuset_hotplug_workfn+0x2ca/0xc90
> > ? balance_push+0x56/0x120
> > ? _raw_spin_unlock+0x15/0x30
> > ? finish_task_switch+0x98/0x2f0
> > ? __switch_to+0x116/0x410
> > ? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
> > ? _raw_spin_unlock_irqrestore+0x23/0x40
> > ? add_timer_on+0xd5/0x130
> > process_one_work+0x1bc/0x3d0
> > worker_thread+0x4c/0x380
> > ? preempt_count_add+0x56/0xa0
> > ? rescuer_thread+0x310/0x310
> > kthread+0xe6/0x110
> > ? kthread_complete_and_exit+0x20/0x20
> > ret_from_fork+0x1f/0x30
> >
> > More detailed key function call graph:
> > rq_offline_rt()
> > __disable_runtime()
> > sched_rt_rq_enqueue()
> > enqueue_top_rt_rq()
> > cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
> > data->func(data, *rq_clock(rq)*, flags)
> > intel_pstate_update_util() <-- powersave policy callback function
> >
> > Before calling rq_offline_rt() we need to update the rq clock to avoid
> > using the old rq clock, So we add update_rq_clock() to set_rq_offline()
> > to update rq clock. And we use rq_lock_irqsave()/rq_unlock_irqrestore()
> > to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore()
> > in rq_attach_root() to ensure that rq->clock_update_flags are cleared
> > before updating the rq clock.
> >
> > Steps to reproduce:
> > 1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
> > 2. echo 1 > /sys/kernel/debug/clear_warn_once
> > 3. cpupower -c all frequency-set -g powersave
> > 4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
> > system with n CPUs)
> > 5. Offline cpu one by one until the warninng is triggered
> >
> > Suggested-by: Ben Segall <[email protected]>
> > Signed-off-by: Hao Jia <[email protected]>
>
> Hi Vincent,
>
> Benjamin Segall suggested adding update_rq_clock() to set_rq_offline()
> instead of calling update_rq_clock() before set_rq_offline() runs.
> The code of patch1 has changed, so I removed your tag "Reviewed-by".
> Please review again.
v5 looks good to me
Reviewed-by: Vincent Guittot <[email protected]>
>
> Thanks,
> Hao
>
> > ---
> > kernel/sched/core.c | 2 +-
> > kernel/sched/topology.c | 6 +++---
> > 2 files changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index a68d1276bab0..a8be5415daba 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -9548,6 +9548,7 @@ void set_rq_offline(struct rq *rq)
> > if (rq->online) {
> > const struct sched_class *class;
> >
> > + update_rq_clock(rq);
> > for_each_class(class) {
> > if (class->rq_offline)
> > class->rq_offline(rq);
> > @@ -9689,7 +9690,6 @@ int sched_cpu_deactivate(unsigned int cpu)
> >
> > rq_lock_irqsave(rq, &rf);
> > if (rq->rd) {
> > - update_rq_clock(rq);
> > BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
> > set_rq_offline(rq);
> > }
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index 6682535e37c8..52976eadfee9 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
> > void rq_attach_root(struct rq *rq, struct root_domain *rd)
> > {
> > struct root_domain *old_rd = NULL;
> > - unsigned long flags;
> > + struct rq_flags rf;
> >
> > - raw_spin_rq_lock_irqsave(rq, flags);
> > + rq_lock_irqsave(rq, &rf);
> >
> > if (rq->rd) {
> > old_rd = rq->rd;
> > @@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
> > if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
> > set_rq_online(rq);
> >
> > - raw_spin_rq_unlock_irqrestore(rq, flags);
> > + rq_unlock_irqrestore(rq, &rf);
> >
> > if (old_rd)
> > call_rcu(&old_rd->rcu, free_rootdomain);
Hao Jia <[email protected]> writes:
> This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
> ------------[ 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
>
> The rq clock has been updated in the set_rq_offline(),
> so we don't need to call update_rq_clock() in
> unthrottle_offline_cfs_rqs().
> We only need to call rq_clock_start_loop_update() before the
> loop starts and rq_clock_stop_loop_update() after the loop
> to avoid this warning.
>
Both of these cfsb patches look sensible to me.
Reviewed-By: Ben Segall <[email protected]>
On Tue, Jun 13, 2023 at 04:20:10PM +0800, Hao Jia wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a8be5415daba..1eca36299d8b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -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
So now you've got update_rq_clock() in both callers, why not remove it
from __balance_push_cpu_stop() ?
Afaict nothing actually needs it before __migrate_task().
---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9435,8 +9435,6 @@ static int __balance_push_cpu_stop(void
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);
On 2023/6/15 Peter Zijlstra wrote:
> On Tue, Jun 13, 2023 at 04:20:10PM +0800, Hao Jia wrote:
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index a8be5415daba..1eca36299d8b 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -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
>
> So now you've got update_rq_clock() in both callers, why not remove it
> from __balance_push_cpu_stop() ?
>
> Afaict nothing actually needs it before __migrate_task().
>
Thanks for your review.
I'm afraid not, the rq clock also needs to be updated before
select_fallback_rq() is called.
> ---
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9435,8 +9435,6 @@ static int __balance_push_cpu_stop(void
> 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);
If we just remove update_rq_clock() from __balance_push_cpu_stop(), we
will get this warning.
[ 1260.960166] rq->clock_update_flags < RQCF_ACT_SKIP
[ 1260.960170] WARNING: CPU: 25 PID: 196 at kernel/sched/sched.h:1496
update_curr+0xf6/0x1f0
[ 1260.960318] Call Trace:
[ 1260.960320] <TASK>
[ 1260.960323] ? show_regs+0x5b/0x60
[ 1260.960327] ? __warn+0x89/0x140
[ 1260.960331] ? update_curr+0xf6/0x1f0
[ 1260.960334] ? report_bug+0x1b7/0x1e0
[ 1260.960338] ? __wake_up_klogd.part.25+0x5a/0x80
[ 1260.960342] ? handle_bug+0x45/0x80
[ 1260.960346] ? exc_invalid_op+0x18/0x70
[ 1260.960348] ? asm_exc_invalid_op+0x1b/0x20
[ 1260.960354] ? update_curr+0xf6/0x1f0
[ 1260.960356] ? update_curr+0xf6/0x1f0
[ 1260.960359] dequeue_entity+0x3b/0x410
[ 1260.960361] dequeue_task_fair+0xc7/0x3c0
[ 1260.960363] dequeue_task+0x30/0xf0
[ 1260.960365] __do_set_cpus_allowed+0x94/0x130
[ 1260.960366] do_set_cpus_allowed+0x38/0x60
[ 1260.960368] cpuset_cpus_allowed_fallback+0x70/0x80
[ 1260.960372] select_fallback_rq+0x20f/0x250 <----
[ 1260.960374] __balance_push_cpu_stop+0x13f/0x1a0
[ 1260.960377] ? migration_cpu_stop+0x2b0/0x2b0
[ 1260.960379] cpu_stopper_thread+0xaf/0x140
[ 1260.960382] smpboot_thread_fn+0x158/0x220
[ 1260.960387] ? sort_range+0x30/0x30
[ 1260.960390] kthread+0xfe/0x130
[ 1260.960392] ? kthread_complete_and_exit+0x20/0x20
[ 1260.960394] ret_from_fork+0x1f/0x30
[ 1260.960399] </TASK>
Thanks,
Hao
On Fri, Jun 16, 2023 at 03:56:25PM +0800, Hao Jia wrote:
> I'm afraid not, the rq clock also needs to be updated before
> select_fallback_rq() is called.
> If we just remove update_rq_clock() from __balance_push_cpu_stop(), we will
> get this warning.
>
>
> [ 1260.960166] rq->clock_update_flags < RQCF_ACT_SKIP
> [ 1260.960170] WARNING: CPU: 25 PID: 196 at kernel/sched/sched.h:1496
> update_curr+0xf6/0x1f0
>
> [ 1260.960318] Call Trace:
> [ 1260.960320] <TASK>
> [ 1260.960359] dequeue_entity+0x3b/0x410
> [ 1260.960361] dequeue_task_fair+0xc7/0x3c0
> [ 1260.960363] dequeue_task+0x30/0xf0
> [ 1260.960365] __do_set_cpus_allowed+0x94/0x130
> [ 1260.960366] do_set_cpus_allowed+0x38/0x60
> [ 1260.960368] cpuset_cpus_allowed_fallback+0x70/0x80
> [ 1260.960372] select_fallback_rq+0x20f/0x250 <----
Urgh... :-(
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 96500560f0c73c71bca1b27536c6254fa0e8ce37
Gitweb: https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
Author: Hao Jia <[email protected]>
AuthorDate: Tue, 13 Jun 2023 16:20:10 +08:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00
sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()
There is a double update_rq_clock() invocation:
__balance_push_cpu_stop()
update_rq_clock()
__migrate_task()
update_rq_clock()
Sadly select_fallback_rq() also needs update_rq_clock() for
__do_set_cpus_allowed(), it is not possible to remove the update from
__balance_push_cpu_stop(). So remove it from __migrate_task() and
ensure all callers of this function call update_rq_clock() prior to
calling it.
Signed-off-by: Hao Jia <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/sched/core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 442efe5..c7db597 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2546,7 +2546,6 @@ 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;
@@ -2604,10 +2603,12 @@ 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
The following commit has been merged into the sched/core branch of tip:
Commit-ID: cab3ecaed5cdcc9c36a96874b4c45056a46ece45
Gitweb: https://git.kernel.org/tip/cab3ecaed5cdcc9c36a96874b4c45056a46ece45
Author: Hao Jia <[email protected]>
AuthorDate: Tue, 13 Jun 2023 16:20:09 +08:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00
sched/core: Fixed missing rq clock update before calling set_rq_offline()
When using a cpufreq governor that uses
cpufreq_add_update_util_hook(), it is possible to trigger a missing
update_rq_clock() warning for the CPU hotplug path:
rq_attach_root()
set_rq_offline()
rq_offline_rt()
__disable_runtime()
sched_rt_rq_enqueue()
enqueue_top_rt_rq()
cpufreq_update_util()
data->func(data, rq_clock(rq), flags)
Move update_rq_clock() from sched_cpu_deactivate() (one of it's
callers) into set_rq_offline() such that it covers all
set_rq_offline() usage.
Additionally change rq_attach_root() to use rq_lock_irqsave() so that
it will properly manage the runqueue clock flags.
Suggested-by: Ben Segall <[email protected]>
Signed-off-by: Hao Jia <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/sched/core.c | 2 +-
kernel/sched/topology.c | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ac38225..442efe5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9585,6 +9585,7 @@ void set_rq_offline(struct rq *rq)
if (rq->online) {
const struct sched_class *class;
+ update_rq_clock(rq);
for_each_class(class) {
if (class->rq_offline)
class->rq_offline(rq);
@@ -9726,7 +9727,6 @@ int sched_cpu_deactivate(unsigned int cpu)
rq_lock_irqsave(rq, &rf);
if (rq->rd) {
- update_rq_clock(rq);
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
set_rq_offline(rq);
}
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index cb92dc5..d3a3b26 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
void rq_attach_root(struct rq *rq, struct root_domain *rd)
{
struct root_domain *old_rd = NULL;
- unsigned long flags;
+ struct rq_flags rf;
- raw_spin_rq_lock_irqsave(rq, flags);
+ rq_lock_irqsave(rq, &rf);
if (rq->rd) {
old_rd = rq->rd;
@@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
set_rq_online(rq);
- raw_spin_rq_unlock_irqrestore(rq, flags);
+ rq_unlock_irqrestore(rq, &rf);
if (old_rd)
call_rcu(&old_rd->rcu, free_rootdomain);
The following commit has been merged into the sched/core branch of tip:
Commit-ID: ebb83d84e49b54369b0db67136a5fe1087124dcc
Gitweb: https://git.kernel.org/tip/ebb83d84e49b54369b0db67136a5fe1087124dcc
Author: Hao Jia <[email protected]>
AuthorDate: Tue, 13 Jun 2023 16:20:11 +08:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Fri, 16 Jun 2023 22:08:13 +02:00
sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()
After commit 8ad075c2eb1f ("sched: Async unthrottling for cfs
bandwidth"), we may update the rq clock multiple times in the loop of
__cfsb_csd_unthrottle().
A prior (although less common) instance of this problem exists in
unthrottle_offline_cfs_rqs().
Cure both by ensuring update_rq_clock() is called before the loop and
setting RQCF_ACT_SKIP during the loop, to supress further updates.
The alternative would be pulling update_rq_clock() out of
unthrottle_cfs_rq(), but that gives an even bigger mess.
Fixes: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
Reviewed-By: Ben Segall <[email protected]>
Suggested-by: Vincent Guittot <[email protected]>
Signed-off-by: Hao Jia <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/sched/fair.c | 18 ++++++++++++++++++
kernel/sched/sched.h | 22 ++++++++++++++++++++++
2 files changed, 40 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7666dbc..a80a739 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5577,6 +5577,14 @@ static void __cfsb_csd_unthrottle(void *arg)
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
* the CSD list. However, this RCU critical section annotates the
* fact that we pair with sched_free_group_rcu(), so that we cannot
@@ -5595,6 +5603,7 @@ static void __cfsb_csd_unthrottle(void *arg)
rcu_read_unlock();
+ rq_clock_stop_loop_update(rq);
rq_unlock(rq, &rf);
}
@@ -6115,6 +6124,13 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
lockdep_assert_rq_held(rq);
+ /*
+ * The rq clock has already been updated in the
+ * set_rq_offline(), 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) {
struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
@@ -6137,6 +6153,8 @@ 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 */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 36e23e4..50d4b61 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1546,6 +1546,28 @@ static inline void rq_clock_cancel_skipupdate(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 clear RQCF_ACT_SKIP of rq->clock_update_flags.
+ */
+static inline void rq_clock_start_loop_update(struct rq *rq)
+{
+ lockdep_assert_rq_held(rq);
+ SCHED_WARN_ON(rq->clock_update_flags & RQCF_ACT_SKIP);
+ 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;
+}
+
struct rq_flags {
unsigned long flags;
struct pin_cookie cookie;
On 2023/6/19 tip-bot2 for Hao Jia wrote:
> The following commit has been merged into the sched/core branch of tip:
>
> Commit-ID: 96500560f0c73c71bca1b27536c6254fa0e8ce37
> Gitweb: https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
> Author: Hao Jia <[email protected]>
> AuthorDate: Tue, 13 Jun 2023 16:20:10 +08:00
> Committer: Peter Zijlstra <[email protected]>
> CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00
>
> sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()
>
> There is a double update_rq_clock() invocation:
>
> __balance_push_cpu_stop()
> update_rq_clock()
> __migrate_task()
> update_rq_clock()
>
> Sadly select_fallback_rq() also needs update_rq_clock() for
> __do_set_cpus_allowed(), it is not possible to remove the update from
> __balance_push_cpu_stop(). So remove it from __migrate_task() and
> ensure all callers of this function call update_rq_clock() prior to
> calling it.
>
Hi Peter,
Thank you very much for refactoring these commit messages to make it
clearer and more concise.
Thanks,
Hao
> Signed-off-by: Hao Jia <[email protected]>
> Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
> Reviewed-by: Vincent Guittot <[email protected]>
> Link: https://lkml.kernel.org/r/[email protected]
> ---
> kernel/sched/core.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 442efe5..c7db597 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2546,7 +2546,6 @@ 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;
> @@ -2604,10 +2603,12 @@ 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