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

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On Sat, 4 Mar 2023 at 16:13, Shrikanth Hegde <sshegde@xxxxxxxxxxxxxxxxxx> wrote:
>
>
>
> 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@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:
> > [...]
> >
> >>>>>>> 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 $$,
> >>> assign the latency nice to cgroup, and run hackbench from that bash prompt.
> >>>
> >>>> I haven't run test such tests in a cgroup but at least the test with
> >>>> latency_nice == 0 should not make any noticeable difference. Does this
> >>>> include the re-arrange patch that you have proposed previously ?
> >>> No. This is only with V12 of the series.
> >>>
> >>>> Also, the tests that you did on v6, gave better result.
> >>>> https://lore.kernel.org/lkml/34112324-de67-55eb-92bc-181a98c4311c@xxxxxxxxxxxxxxxxxx/
> >>>>
> >>>> Are you running same tests or you changed something in the mean time ?
> >>> Test machine got changed.
> >>> now i re-read my earlier mail. I see it was slightly different.
> >>> I had created only one cgroup and stress-ng was run
> >>> without any cgroup. Let me try that scenario and get the numbers.
> >>
> >> Tried the same method of testing i had done on V7 of the series. on this
> >> machine hackbench still regress's both on V12 as well as V7 of the series.
> >>
> >> Created one cpu cgroup called cgroup1. created two bash prompts.
> >> assigned "bash $$" 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.

Great. At least we have narrow the problem to one f the 3 changes.

> 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?

Yes, would be good to know which of the 3 changes in the patch create
the regression

I suspect the 1st change to be the root cause of your problem but It
would be good if you can confirm my assumption with some tests

Thanks

>
> >> 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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