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Message-ID: <48b8f849-fa81-d968-8fb6-b25c5fe94edb@linux.vnet.ibm.com>
Date:   Sat, 4 Mar 2023 20:41:06 +0530
From:   Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, qperret@...gle.com,
        tim.c.chen@...ux.intel.com, joshdon@...gle.com, timj@....org,
        kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com, tj@...nel.org,
        lizefan.x@...edance.com, hannes@...xchg.org,
        cgroups@...r.kernel.org, corbet@....net, linux-doc@...r.kernel.org,
        Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
Subject: Re: [PATCH v12 8/8] sched/fair: Add latency list



On 3/3/23 10:01 PM, Vincent Guittot wrote:
> Le jeudi 02 mars 2023 à 23:37:52 (+0530), Shrikanth Hegde a écrit :
>>
>> On 3/2/23 8:30 PM, Shrikanth Hegde wrote:
>>> On 3/2/23 6:47 PM, Vincent Guittot wrote:
>>>> On Thu, 2 Mar 2023 at 12:00, Shrikanth Hegde <sshegde@...ux.vnet.ibm.com> wrote:
>>>>> On 3/2/23 1:20 PM, Vincent Guittot wrote:
>>>>>> On Wed, 1 Mar 2023 at 19:48, shrikanth hegde <sshegde@...ux.vnet.ibm.com> wrote:
>>>>>>> On 2/24/23 3:04 PM, Vincent Guittot wrote:
> [...]
>
>>>>>>> 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 $$, 
>>> assign the latency nice to cgroup, and run hackbench from that bash prompt.
>>>
>>>> I haven't run test such tests in a cgroup but at least the test with
>>>> latency_nice == 0 should not make any noticeable difference. Does this
>>>> include the re-arrange patch that you have proposed previously ?
>>> No. This is only with V12 of the series.
>>>
>>>> Also, the tests that you did on v6, gave better result.
>>>> https://lore.kernel.org/lkml/34112324-de67-55eb-92bc-181a98c4311c@linux.vnet.ibm.com/
>>>>
>>>> Are you running same tests or you changed something in the mean time ?
>>> Test machine got changed. 
>>> now i re-read my earlier mail. I see it was slightly different. 
>>> I had created only one cgroup and stress-ng was run
>>> without any cgroup. Let me try that scenario and get the numbers. 
>>
>> Tried the same method of testing i had done on V7 of the series. on this
>> machine hackbench still regress's both on V12 as well as V7 of the series.
>>
>> Created one cpu cgroup called cgroup1. created two bash prompts. 
>> assigned "bash $$" to cgroup1 and on other bash prompt running,
>> stress-ng --cpu=96 -l 50. Ran hackbench from cgroup1 prompt. 
>> assigned latency values to the cgroup1.
> I have tried to reproduce your results on some of my systems but I can't see
> the impacts that you are reporting below.
> The fact that your other platform was not impacted as well could imply that
> it's specific to this platform.
> In particular, the lat nice=0 case should not show any real impact as it
> should be similar to a nop. At least that what I can see in the tests on my
> platforms and Prateek on his.
>
> Nevertheless, could you try to run your tests with the changes below ?
> These are the only places which could have an impact even with lat nice = 0
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8137bca80572..979571a98b28 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4991,8 +4991,7 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
>         if (delta < offset)
>                 return;
>
> -       if ((delta > ideal_runtime) ||
> -           (delta > get_latency_max()))
> +       if (delta > ideal_runtime)
>                 resched_curr(rq_of(cfs_rq));
>  }
>
> @@ -7574,9 +7573,10 @@ static long wakeup_latency_gran(struct sched_entity *curr, struct sched_entity *
>          * Otherwise, use the latency weight to evaluate how much scheduling
>          * delay is acceptable by se.
>          */
> -       if ((latency_offset < 0) || (curr->latency_offset < 0))
> +       if ((latency_offset < 0) || (curr->latency_offset < 0)) {
>                 latency_offset -= curr->latency_offset;
> -       latency_offset = min_t(long, latency_offset, get_latency_max());
> +               latency_offset = min_t(long, latency_offset, get_latency_max());
> +       }
>
>         return latency_offset;
>  }
> @@ -7635,7 +7635,6 @@ wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
>          * for low priority task. Make sure that long sleeping task will get a
>          * chance to preempt current.
>          */
> -       gran = min_t(s64, gran, get_latency_max());
>
>         if (vdiff > gran)
>                 return 1;
>

Above patch helps. thank you.
Numbers are comparable to 6.2 and there is slight improvement. Much better than V12 numbers. 

type	   groups |   v6.2      |v6.2 + V12| v6.2 + V12  | v6.2 + V12
		  |	        |lat nice=0| lat nice=-20| lat nice=+19

Process	      10  |	0.33    |   0.37   |   0.38     |   0.37
Process       20  |	0.61    |   0.67   |   0.68     |   0.67
Process	      30  |	0.85    |   0.95   |   0.95     |   0.96
Process	      40  |	1.10    |   1.20   |   1.20     |   1.21
Process	      50  |	1.34    |   1.47   |   1.44     |   1.45
Process	      60  |	1.57    |   1.70   |   1.71     |   1.70
thread	      10  |	0.36    |   0.40   |   0.39     |   0.39
thread	      20  |	0.65    |   0.72   |   0.71     |   0.71
Process(Pipe) 10  |	0.18	|   0.31   |   0.31	|   0.33
Process(Pipe) 20  |	0.32	|   0.51   |   0.50	|   0.50
Process(Pipe) 30  |	0.43	|   0.65   |   0.67	|   0.67
Process(Pipe) 40  |	0.57	|   0.82   |   0.83	|   0.83
Process(Pipe) 50  |	0.67	|   1.00   |   0.97	|   0.98
Process(Pipe) 60  |	0.81	|   1.13   |   1.11	|   1.12
thread(Pipe)  10  |	0.19	|   0.33   |   0.33	|   0.33
thread(Pipe)  20  |	0.34	|   0.53   |   0.51	|   0.52



type	   groups |   v6.2	|v6.2+ V12+ | v6.2 + V12+| v6.2 + V12
                  |             |above patch|above patch | above patch
		  |		|lat nice=0 |lat nice=-20| lat nice=+19

Process       10  |	0.36    |   0.33    |   0.34     |   0.34
Process       20  |	0.62    |   0.60    |   0.61     |   0.61
Process       30  |	0.87    |   0.84    |   0.85     |   0.84
Process       40  |	1.13    |   1.09    |   1.10     |   1.09
Process       50  |	1.38    |   1.33    |   1.33     |   1.34
Process       60  |	1.64    |   1.56    |   1.58     |   1.56
thread        10  |	0.35    |   0.35    |   0.35     |   0.35
thread        20  |	0.64    |   0.63    |   0.63     |   0.63
Process(Pipe) 10  |	0.20    |   0.18    |   0.18     |   0.18
Process(Pipe) 20  |	0.32    |   0.31    |   0.31     |   0.32
Process(Pipe) 30  |	0.44    |   0.43    |   0.43     |   0.43
Process(Pipe) 40  |	0.56    |   0.57    |   0.56     |   0.55
Process(Pipe) 50  |	0.70    |   0.67    |   0.67     |   0.67
Process(Pipe) 60  |	0.83    |   0.79    |   0.81     |   0.80
thread(Pipe)  10  |	0.21    |   0.19    |   0.19     |   0.19
thread(Pipe)  20  |	0.35    |   0.33    |   0.34     |   0.33


Do you want me to try any other experiment on this further?

>> I will try to run with only task's set with latency_nice=0 as well. 
>>
>> type	   groups |   v6.2      |v6.2 + V12| v6.2 + V12  | v6.2 + V12
>> 		  |	        |lat nice=0| lat nice=-20| lat nice=+19
>>
>> Process	      10  |	0.33    |   0.37   |   0.38     |   0.37
>> Process       20  |	0.61    |   0.67   |   0.68     |   0.67
>> Process	      30  |	0.85    |   0.95   |   0.95     |   0.96
>> Process	      40  |	1.10    |   1.20   |   1.20     |   1.21
>> Process	      50  |	1.34    |   1.47   |   1.44     |   1.45
>> Process	      60  |	1.57    |   1.70   |   1.71     |   1.70
>> thread	      10  |	0.36    |   0.40   |   0.39     |   0.39
>> thread	      20  |	0.65    |   0.72   |   0.71     |   0.71
>> Process(Pipe) 10  |	0.18	|   0.31   |   0.31	|   0.33
>> Process(Pipe) 20  |	0.32	|   0.51   |   0.50	|   0.50
>> Process(Pipe) 30  |	0.43	|   0.65   |   0.67	|   0.67
>> Process(Pipe) 40  |	0.57	|   0.82   |   0.83	|   0.83
>> Process(Pipe) 50  |	0.67	|   1.00   |   0.97	|   0.98
>> Process(Pipe) 60  |	0.81	|   1.13   |   1.11	|   1.12
>> thread(Pipe)  10  |	0.19	|   0.33   |   0.33	|   0.33
>> thread(Pipe)  20  |	0.34	|   0.53   |   0.51	|   0.52
>>
>>
>>
>> type	   groups |   v6.2	|v6.2 + V7 | v6.2 + V7  | v6.2 + V7
>> 		  |		|lat nice=0|lat nice=-20| lat nice=+19
>> Process	      10  |	0.33    |   0.37   |   0.37     |   0.37
>> Process	      20  |	0.61    |   0.67   |   0.67     |   0.67
>> Process	      30  |	0.85    |   0.96   |   0.94     |   0.95
>> Process	      40  |	1.10    |   1.20   |   1.20     |   1.20
>> Process	      50  |	1.34    |   1.45   |   1.46     |   1.45
>> Process	      60  |	1.57    |   1.71   |   1.68     |   1.72
>> thread	      10  |	0.36    |   0.40   |   0.40     |   0.40
>> thread	      20  |	0.65    |   0.71   |   0.71     |   0.71
>> Process(Pipe) 10  |	0.18	|   0.30   |   0.30	|   0.31
>> Process(Pipe) 20  |	0.32	|   0.50   |   0.50	|   0.50
>> Process(Pipe) 30  |	0.43	|   0.67   |   0.67	|   0.66
>> Process(Pipe) 40  |	0.57	|   0.86   |   0.84	|   0.84
>> Process(Pipe) 50  |	0.67	|   0.99   |   0.97	|   0.97
>> Process(Pipe) 60  |	0.81	|   1.10   |   1.13	|   1.13
>> thread(Pipe)  10  |	0.19	|   0.34   |   0.34	|   0.33
>> thread(Pipe)  20  |	0.34	|   0.55   |   0.53	|   0.54
>>
>>>>> 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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