Re: [PATCH v12 8/8] sched/fair: Add latency list

From: Shrikanth Hegde
Date: Thu Mar 02 2023 - 10:02:16 EST

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In reply to: Vincent Guittot: "Re: [PATCH v12 8/8] sched/fair: Add latency list"
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On 3/2/23 6:47 PM, Vincent Guittot wrote:
> On Thu, 2 Mar 2023 at 12:00, Shrikanth Hegde <sshegde@xxxxxxxxxxxxxxxxxx> wrote:
>>
>> On 3/2/23 1:20 PM, Vincent Guittot wrote:
>>> On Wed, 1 Mar 2023 at 19:48, shrikanth hegde <sshegde@xxxxxxxxxxxxxxxxxx> wrote:
>>>> On 2/24/23 3:04 PM, Vincent Guittot wrote:
>>>>> Add a rb tree for latency sensitive entities so we can schedule the most
>>>>> sensitive one first even when it failed to preempt current at wakeup or
>>>>> when it got quickly preempted by another entity of higher priority.
>>>>>
>>>>> In order to keep fairness, the latency is used once at wakeup to get a
>>>>> minimum slice and not during the following scheduling slice to prevent
>>>>> long running entity to got more running time than allocated to his nice
>>>>> priority.
>>>>>
>>>>> The rb tree enables to cover the last corner case where latency
>>>>> sensitive entity can't got schedule quickly after the wakeup.
>>>>>
>>>>> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>>>>> Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
>>>>> ---
>>>>> include/linux/sched.h | 1 +
>>>>> kernel/sched/core.c | 1 +
>>>>> kernel/sched/fair.c | 109 ++++++++++++++++++++++++++++++++++++++++--
>>>>> kernel/sched/sched.h | 1 +
>>>>> 4 files changed, 109 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>>>> index 38decae3e156..41bb92be5ecc 100644
>>>>> --- a/include/linux/sched.h
>>>>> +++ b/include/linux/sched.h
>>>>> @@ -548,6 +548,7 @@ struct sched_entity {
>>>>> /* For load-balancing: */
>>>>> struct load_weight load;
>>>>> struct rb_node run_node;
>>>>> + struct rb_node latency_node;
>>>> Ran pahole to see if the frequently accessed fields change across cachelines.
>>>> There is no change in cachelines of task_struct, whereas sched_entity differs
>>>> due to latency_node. Maybe the latency_node could be placed after
>>>> runnable_weight as there is space available in that cacheline.
>>> I will run some test on my system to confimr your results but we can
>>> move latency_node field if it helps cache hit stats
>>>
>>>> 6.2
>>>> #pahole sched_entity
>>>> struct sched_entity {
>>>> struct load_weight load; /* 0 16 */
>>>>
>>>> /* XXX last struct has 4 bytes of padding */
>>>>
>>>> struct rb_node run_node; /* 16 24 */
>>>> struct list_head group_node; /* 40 16 */
>>>> unsigned int on_rq; /* 56 4 */
>>>>
>>>> /* XXX 4 bytes hole, try to pack */
>>>>
>>>> u64 exec_start; /* 64 8 */
>>>> u64 sum_exec_runtime; /* 72 8 */
>>>> u64 vruntime; /* 80 8 */
>>>> u64 prev_sum_exec_runtime; /* 88 8 */
>>>> u64 nr_migrations; /* 96 8 */
>>>> int depth; /* 104 4 */
>>>>
>>>> /* XXX 4 bytes hole, try to pack */
>>>>
>>>> struct sched_entity * parent; /* 112 8 */
>>>> struct cfs_rq * cfs_rq; /* 120 8 */
>>>> /* --- cacheline 1 boundary (128 bytes) --- */
>>>> struct cfs_rq * my_q; /* 128 8 */
>>>> long unsigned int runnable_weight; /* 136 8 */
>>>>
>>>> /* XXX 112 bytes hole, try to pack */
>>>>
>>>> /* --- cacheline 2 boundary (256 bytes) --- */
>>>> struct sched_avg avg; /* 256 128 */
>>>>
>>>>
>>>> 6.2 + V12 patch
>>>> #pahole sched_entity
>>>> struct sched_entity {
>>>> struct load_weight load; /* 0 16 */
>>>>
>>>> /* XXX last struct has 4 bytes of padding */
>>>>
>>>> struct rb_node run_node; /* 16 24 */
>>>> struct rb_node latency_node; /* 40 24 */
>>>> struct list_head group_node; /* 64 16 */
>>>> unsigned int on_rq; /* 80 4 */
>>>>
>>>> /* XXX 4 bytes hole, try to pack */
>>>>
>>>> u64 exec_start; /* 88 8 */
>>>> u64 sum_exec_runtime; /* 96 8 */
>>>> u64 vruntime; /* 104 8 */
>>>> u64 prev_sum_exec_runtime; /* 112 8 */
>>>> u64 nr_migrations; /* 120 8 */
>>>> /* --- cacheline 1 boundary (128 bytes) --- */
>>>> int depth; /* 128 4 */
>>>>
>>>> /* XXX 4 bytes hole, try to pack */
>>>>
>>>> struct sched_entity * parent; /* 136 8 */
>>>> struct cfs_rq * cfs_rq; /* 144 8 */
>>>> struct cfs_rq * my_q; /* 152 8 */
>>>>
>>>>
>>>> 6.2 + V12 patch + Re-shuffle of latency_node
>>>> #pahole sched_entity
>>>> struct sched_entity {
>>>> struct load_weight load; /* 0 16 */
>>>>
>>>> /* XXX last struct has 4 bytes of padding */
>>>>
>>>> struct rb_node run_node; /* 16 24 */
>>>> struct list_head group_node; /* 40 16 */
>>>> unsigned int on_rq; /* 56 4 */
>>>>
>>>> /* XXX 4 bytes hole, try to pack */
>>>>
>>>> u64 exec_start; /* 64 8 */
>>>> u64 sum_exec_runtime; /* 72 8 */
>>>> u64 vruntime; /* 80 8 */
>>>> u64 prev_sum_exec_runtime; /* 88 8 */
>>>> u64 nr_migrations; /* 96 8 */
>>>> int depth; /* 104 4 */
>>>>
>>>> /* XXX 4 bytes hole, try to pack */
>>>>
>>>> struct sched_entity * parent; /* 112 8 */
>>>> struct cfs_rq * cfs_rq; /* 120 8 */
>>>> /* --- cacheline 1 boundary (128 bytes) --- */
>>>> struct cfs_rq * my_q; /* 128 8 */
>>>> long unsigned int runnable_weight; /* 136 8 */
>>>> struct rb_node latency_node; /* 144 24 */
>>>> long int latency_offset; /* 168 8 */
>>>>
>>>> /* XXX 80 bytes hole, try to pack */
>>>>
>>>> /* --- cacheline 2 boundary (256 bytes) --- */
>>>>
>>>>
>>>>
>>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>>> index a2b52cf5e1bb..1e93aaaeead2 100644
>>>> --- a/include/linux/sched.h
>>>> +++ b/include/linux/sched.h
>>>> @@ -548,7 +548,6 @@ struct sched_entity {
>>>> /* For load-balancing: */
>>>> struct load_weight load;
>>>> struct rb_node run_node;
>>>> - struct rb_node latency_node;
>>>> struct list_head group_node;
>>>> unsigned int on_rq;
>>>>
>>>> @@ -569,6 +568,7 @@ struct sched_entity {
>>>> /* cached value of my_q->h_nr_running */
>>>> unsigned long runnable_weight;
>>>> #endif
>>>> + struct rb_node latency_node;
>>>> /* preemption offset in ns */
>>>> long latency_offset;
>>>>
>>>>
>>>> Ran the schbench and hackbench with this patch series. Here comparison is
>>>> between 6.2 stable tree, 6.2 + Patch and 6.2 + patch + above re-arrange of
>>>> latency_node. Ran two cgroups, in one cgroup running stress-ng at 50%(group1)
>>>> and other is running these benchmarks (group2). Set the latency nice
>>>> of group2 to -20. These are run on Power system with 12 cores with SMT=8.
>>>> Total of 96 CPU.
>>>>
>>>> schbench gets lower latency compared to stabletree. Whereas hackbench seems
>>>> to regress under this case. Maybe i am doing something wrong. I will re-run
>>>> and attach the numbers to series.
>>>> Please suggest if any variation in the test i need to try.
>>> hackbench takes advanatge of a latency nice 19 as it mainly wants to
>>> run longer slice to move forward rather than preempting others all the
>>> time
>> hackbench still seems to regress in different latency nice values compared to
>> baseline of 6.2 in this case. up to 50% in some cases.
>>
>> 12 core powerpc system with SMT=8 i.e 96 CPU
>> running 2 CPU cgroups. No quota assigned.
>> 1st cgroup is running stress-ng with 48 threads. Consuming 50% of CPU.
>> latency is not changed for this cgroup.
>> 2nd cgroup is running hackbench. This cgroup is assigned the different latency
>> nice values of 0, -20 and 19.
> According to your other emails, you are using the cgroup interface and
> not the task's one. Do I get it right ?

right. I create cgroup, attach bash command with echo $$,
assign the latency nice to cgroup, and run hackbench from that bash prompt.

>
> I haven't run test such tests in a cgroup but at least the test with
> latency_nice == 0 should not make any noticeable difference. Does this
> include the re-arrange patch that you have proposed previously ?

No. This is only with V12 of the series.

>
> Also, the tests that you did on v6, gave better result.
> https://lore.kernel.org/lkml/34112324-de67-55eb-92bc-181a98c4311c@xxxxxxxxxxxxxxxxxx/
>
> Are you running same tests or you changed something in the mean time ?

Test machine got changed.
now i re-read my earlier mail. I see it was slightly different.
I had created only one cgroup and stress-ng was run
without any cgroup. Let me try that scenario and get the numbers.

>
>> Numbers are average of 10 runs in each case. Time is in seconds
>>
>> type groups | v6.2 | v6.2 + V12 | v6.2 + V12 | v6.2 + V12
>> | | lat nice=0 | lat nice=-20| lat nice=+19
>> | | | |
>> Process 10 | 0.36 | 0.41 | 0.43 | 0.42
>> Process 20 | 0.62 | 0.76 | 0.75 | 0.75
>> Process 30 | 0.87 | 1.05 | 1.04 | 1.06
>> Process 40 | 1.13 | 1.34 | 1.33 | 1.33
>> Process 50 | 1.38 | 1.62 | 1.66 | 1.63
>> Process 60 | 1.64 | 1.91 | 1.97 | 1.90
>> thread 10 | 0.35 | 0.41 | 0.44 | 0.42
>> thread 20 | 0.64 | 0.78 | 0.77 | 0.79
>> Process(Pipe) 10 | 0.20 | 0.34 | 0.33 | 0.34
>> Process(Pipe) 20 | 0.32 | 0.52 | 0.53 | 0.52
>> Process(Pipe) 30 | 0.44 | 0.70 | 0.70 | 0.69
>> Process(Pipe) 40 | 0.56 | 0.88 | 0.89 | 0.88
>> Process(Pipe) 50 | 0.70 | 1.08 | 1.08 | 1.07
>> Process(Pipe) 60 | 0.83 | 1.27 | 1.27 | 1.26
>> thread(Pipe) 10 | 0.21 | 0.35 | 0.34 | 0.36
>> thread(Pipe) 10 | 0.35 | 0.55 | 0.58 | 0.55
>>
>>
>>
>>>> Re-arrange seems to help the patch series by avoiding an cacheline miss.
>>>>
>>>> =========================
>>>> schbench
>>>> =========================
>>>> 6.2 | 6.2 + V12 | 6.2 + V12 + re-arrange
>>>> 1 Thread
>>>> 50.0th: 9.00 | 9.00 | 9.50
>>>> 75.0th: 10.50 | 10.00 | 9.50
>>>> 90.0th: 11.00 | 11.00 | 10.50
>>>> 95.0th: 11.00 | 11.00 | 11.00
>>>> 99.0th: 11.50 | 11.50 | 11.50
>>>> 99.5th: 12.50 | 12.00 | 12.00
>>>> 99.9th: 14.50 | 13.50 | 12.00
>>>> 2 Threads
>>>> 50.0th: 9.50 | 9.50 | 8.50
>>>> 75.0th: 11.00 | 10.50 | 9.50
>>>> 90.0th: 13.50 | 11.50 | 10.50
>>>> 95.0th: 14.00 | 12.00 | 11.00
>>>> 99.0th: 15.50 | 13.50 | 12.00
>>>> 99.5th: 16.00 | 14.00 | 12.00
>>>> 99.9th: 17.00 | 16.00 | 16.50
>>>> 4 Threads
>>>> 50.0th: 11.50 | 11.50 | 10.50
>>>> 75.0th: 13.50 | 12.50 | 12.50
>>>> 90.0th: 15.50 | 14.50 | 14.00
>>>> 95.0th: 16.50 | 15.50 | 14.50
>>>> 99.0th: 20.00 | 17.50 | 16.50
>>>> 99.5th: 20.50 | 18.50 | 17.00
>>>> 99.9th: 22.50 | 21.00 | 19.00
>>>> 8 Threads
>>>> 50.0th: 14.00 | 14.00 | 14.00
>>>> 75.0th: 16.00 | 16.00 | 16.00
>>>> 90.0th: 18.00 | 18.00 | 17.50
>>>> 95.0th: 18.50 | 18.50 | 18.50
>>>> 99.0th: 20.00 | 20.00 | 20.00
>>>> 99.5th: 20.50 | 21.50 | 21.00
>>>> 99.9th: 22.50 | 23.50 | 23.00
>>>> 16 Threads
>>>> 50.0th: 19.00 | 18.50 | 19.00
>>>> 75.0th: 23.00 | 22.50 | 23.00
>>>> 90.0th: 25.00 | 25.50 | 25.00
>>>> 95.0th: 26.50 | 26.50 | 26.00
>>>> 99.0th: 28.50 | 29.00 | 28.50
>>>> 99.5th: 31.00 | 30.00 | 30.00
>>>> 99.9th: 5626.00 | 4761.50 | 32.50
>>>> 32 Threads
>>>> 50.0th: 27.00 | 27.50 | 29.00
>>>> 75.0th: 35.50 | 36.50 | 38.50
>>>> 90.0th: 42.00 | 44.00 | 50.50
>>>> 95.0th: 447.50 | 2959.00 | 8544.00
>>>> 99.0th: 7372.00 | 17032.00 | 19136.00
>>>> 99.5th: 15360.00 | 19808.00 | 20704.00
>>>> 99.9th: 20640.00 | 30048.00 | 30048.00
>>>>
>>>> ====================
>>>> hackbench
>>>> ====================
>>>> 6.2 | 6.2 + V12 | 6.2+ V12 +re-arrange
>>>>
>>>> Process 10 Time: 0.35 | 0.42 | 0.41
>>>> Process 20 Time: 0.61 | 0.76 | 0.76
>>>> Process 30 Time: 0.87 | 1.06 | 1.05
>>>> thread 10 Time: 0.35 | 0.43 | 0.42
>>>> thread 20 Time: 0.66 | 0.79 | 0.78
>>>> Process(Pipe) 10 Time: 0.21 | 0.33 | 0.32
>>>> Process(Pipe) 20 Time: 0.34 | 0.52 | 0.52
>>>> Process(Pipe) 30 Time: 0.46 | 0.72 | 0.71
>>>> thread(Pipe) 10 Time: 0.21 | 0.34 | 0.34
>>>> thread(Pipe) 20 Time: 0.36 | 0.56 | 0.56
>>>>
>>>>
>>>>> struct list_head group_node;
>>>>> unsigned int on_rq;
>>>>>
>>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>>>> index 093cc1af73dc..752fd364216c 100644
>>>>> --- a/kernel/sched/core.c
>>>>> +++ b/kernel/sched/core.c
>>>>> @@ -4434,6 +4434,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>>>>> p->se.nr_migrations = 0;
>>>>> p->se.vruntime = 0;
>>>>> INIT_LIST_HEAD(&p->se.group_node);
>>>>> + RB_CLEAR_NODE(&p->se.latency_node);
>>>>>
>>>>> #ifdef CONFIG_FAIR_GROUP_SCHED
>>>>> p->se.cfs_rq = NULL;
>>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>>> index 125a6ff53378..e2aeb4511686 100644
>>>>> --- a/kernel/sched/fair.c
>>>>> +++ b/kernel/sched/fair.c
>>>>> @@ -680,7 +680,85 @@ struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
>>>>>
>>>>> return __node_2_se(last);
>>>>> }
>>>>> +#endif
>>>>>
>>>>> +/**************************************************************
>>>>> + * Scheduling class tree data structure manipulation methods:
>>>>> + * for latency
>>>>> + */
>>>>> +
>>>>> +static inline bool latency_before(struct sched_entity *a,
>>>>> + struct sched_entity *b)
>>>>> +{
>>>>> + return (s64)(a->vruntime + a->latency_offset - b->vruntime - b->latency_offset) < 0;
>>>>> +}
>>>>> +
>>>>> +#define __latency_node_2_se(node) \
>>>>> + rb_entry((node), struct sched_entity, latency_node)
>>>>> +
>>>>> +static inline bool __latency_less(struct rb_node *a, const struct rb_node *b)
>>>>> +{
>>>>> + return latency_before(__latency_node_2_se(a), __latency_node_2_se(b));
>>>>> +}
>>>>> +
>>>>> +/*
>>>>> + * Enqueue an entity into the latency rb-tree:
>>>>> + */
>>>>> +static void __enqueue_latency(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>>>>> +{
>>>>> +
>>>>> + /* Only latency sensitive entity can be added to the list */
>>>>> + if (se->latency_offset >= 0)
>>>>> + return;
>>>>> +
>>>>> + if (!RB_EMPTY_NODE(&se->latency_node))
>>>>> + return;
>>>>> +
>>>>> + /*
>>>>> + * The entity is always added the latency list at wakeup.
>>>>> + * Then, a not waking up entity that is put back in the list after an
>>>>> + * execution time less than sysctl_sched_min_granularity, means that
>>>>> + * the entity has been preempted by a higher sched class or an entity
>>>>> + * with higher latency constraint. In thi case, the entity is also put
>>>>> + * back in the latency list so it gets a chance to run 1st during the
>>>>> + * next slice.
>>>>> + */
>>>>> + if (!(flags & ENQUEUE_WAKEUP)) {
>>>>> + u64 delta_exec = se->sum_exec_runtime - se->prev_sum_exec_runtime;
>>>>> +
>>>>> + if (delta_exec >= sysctl_sched_min_granularity)
>>>>> + return;
>>>>> + }
>>>>> +
>>>>> + rb_add_cached(&se->latency_node, &cfs_rq->latency_timeline, __latency_less);
>>>>> +}
>>>>> +
>>>>> +/*
>>>>> + * Dequeue an entity from the latency rb-tree and return true if it was really
>>>>> + * part of the rb-tree:
>>>>> + */
>>>>> +static bool __dequeue_latency(struct cfs_rq *cfs_rq, struct sched_entity *se)
>>>>> +{
>>>>> + if (!RB_EMPTY_NODE(&se->latency_node)) {
>>>>> + rb_erase_cached(&se->latency_node, &cfs_rq->latency_timeline);
>>>>> + RB_CLEAR_NODE(&se->latency_node);
>>>>> + return true;
>>>>> + }
>>>>> +
>>>>> + return false;
>>>>> +}
>>>>> +
>>>>> +static struct sched_entity *__pick_first_latency(struct cfs_rq *cfs_rq)
>>>>> +{
>>>>> + struct rb_node *left = rb_first_cached(&cfs_rq->latency_timeline);
>>>>> +
>>>>> + if (!left)
>>>>> + return NULL;
>>>>> +
>>>>> + return __latency_node_2_se(left);
>>>>> +}
>>>>> +
>>>>> +#ifdef CONFIG_SCHED_DEBUG
>>>>> /**************************************************************
>>>>> * Scheduling class statistics methods:
>>>>> */
>>>>> @@ -4758,8 +4836,10 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>>>>> check_schedstat_required();
>>>>> update_stats_enqueue_fair(cfs_rq, se, flags);
>>>>> check_spread(cfs_rq, se);
>>>>> - if (!curr)
>>>>> + if (!curr) {
>>>>> __enqueue_entity(cfs_rq, se);
>>>>> + __enqueue_latency(cfs_rq, se, flags);
>>>>> + }
>>>>> se->on_rq = 1;
>>>>>
>>>>> if (cfs_rq->nr_running == 1) {
>>>>> @@ -4845,8 +4925,10 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>>>>>
>>>>> clear_buddies(cfs_rq, se);
>>>>>
>>>>> - if (se != cfs_rq->curr)
>>>>> + if (se != cfs_rq->curr) {
>>>>> __dequeue_entity(cfs_rq, se);
>>>>> + __dequeue_latency(cfs_rq, se);
>>>>> + }
>>>>> se->on_rq = 0;
>>>>> account_entity_dequeue(cfs_rq, se);
>>>>>
>>>>> @@ -4941,6 +5023,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
>>>>> */
>>>>> update_stats_wait_end_fair(cfs_rq, se);
>>>>> __dequeue_entity(cfs_rq, se);
>>>>> + __dequeue_latency(cfs_rq, se);
>>>>> update_load_avg(cfs_rq, se, UPDATE_TG);
>>>>> }
>>>>>
>>>>> @@ -4979,7 +5062,7 @@ static struct sched_entity *
>>>>> pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
>>>>> {
>>>>> struct sched_entity *left = __pick_first_entity(cfs_rq);
>>>>> - struct sched_entity *se;
>>>>> + struct sched_entity *latency, *se;
>>>>>
>>>>> /*
>>>>> * If curr is set we have to see if its left of the leftmost entity
>>>>> @@ -5021,6 +5104,12 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
>>>>> se = cfs_rq->last;
>>>>> }
>>>>>
>>>>> + /* Check for latency sensitive entity waiting for running */
>>>>> + latency = __pick_first_latency(cfs_rq);
>>>>> + if (latency && (latency != se) &&
>>>>> + wakeup_preempt_entity(latency, se) < 1)
>>>>> + se = latency;
>>>>> +
>>>>> return se;
>>>>> }
>>>>>
>>>>> @@ -5044,6 +5133,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
>>>>> update_stats_wait_start_fair(cfs_rq, prev);
>>>>> /* Put 'current' back into the tree. */
>>>>> __enqueue_entity(cfs_rq, prev);
>>>>> + __enqueue_latency(cfs_rq, prev, 0);
>>>>> /* in !on_rq case, update occurred at dequeue */
>>>>> update_load_avg(cfs_rq, prev, 0);
>>>>> }
>>>>> @@ -12222,6 +12312,7 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
>>>>> void init_cfs_rq(struct cfs_rq *cfs_rq)
>>>>> {
>>>>> cfs_rq->tasks_timeline = RB_ROOT_CACHED;
>>>>> + cfs_rq->latency_timeline = RB_ROOT_CACHED;
>>>>> u64_u32_store(cfs_rq->min_vruntime, (u64)(-(1LL << 20)));
>>>>> #ifdef CONFIG_SMP
>>>>> raw_spin_lock_init(&cfs_rq->removed.lock);
>>>>> @@ -12378,6 +12469,7 @@ void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
>>>>> se->my_q = cfs_rq;
>>>>>
>>>>> se->latency_offset = calc_latency_offset(tg->latency_prio);
>>>>> + RB_CLEAR_NODE(&se->latency_node);
>>>>>
>>>>> /* guarantee group entities always have weight */
>>>>> update_load_set(&se->load, NICE_0_LOAD);
>>>>> @@ -12529,8 +12621,19 @@ int sched_group_set_latency(struct task_group *tg, int prio)
>>>>>
>>>>> for_each_possible_cpu(i) {
>>>>> struct sched_entity *se = tg->se[i];
>>>>> + struct rq *rq = cpu_rq(i);
>>>>> + struct rq_flags rf;
>>>>> + bool queued;
>>>>> +
>>>>> + rq_lock_irqsave(rq, &rf);
>>>>>
>>>>> + queued = __dequeue_latency(se->cfs_rq, se);
>>>>> WRITE_ONCE(se->latency_offset, latency_offset);
>>>>> + if (queued)
>>>>> + __enqueue_latency(se->cfs_rq, se, ENQUEUE_WAKEUP);
>>>>> +
>>>>> +
>>>>> + rq_unlock_irqrestore(rq, &rf);
>>>>> }
>>>>>
>>>>> mutex_unlock(&shares_mutex);
>>>>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>>>>> index 9a2e71231083..21dd309e98a9 100644
>>>>> --- a/kernel/sched/sched.h
>>>>> +++ b/kernel/sched/sched.h
>>>>> @@ -570,6 +570,7 @@ struct cfs_rq {
>>>>> #endif
>>>>>
>>>>> struct rb_root_cached tasks_timeline;
>>>>> + struct rb_root_cached latency_timeline;
>>>>>
>>>>> /*
>>>>> * 'curr' points to currently running entity on this cfs_rq.

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