Re: [PATCH -tip 14/32] sched: migration changes for core scheduling

[Li, Aubrey]

On 2020/11/30 18:35, Vincent Guittot wrote:
> On Wed, 18 Nov 2020 at 00:20, Joel Fernandes (Google)
> <joel@xxxxxxxxxxxxxxxxx> wrote:
>>
>> From: Aubrey Li <aubrey.li@xxxxxxxxx>
>>
>>  - Don't migrate if there is a cookie mismatch
>>      Load balance tries to move task from busiest CPU to the
>>      destination CPU. When core scheduling is enabled, if the
>>      task's cookie does not match with the destination CPU's
>>      core cookie, this task will be skipped by this CPU. This
>>      mitigates the forced idle time on the destination CPU.
>>
>>  - Select cookie matched idle CPU
>>      In the fast path of task wakeup, select the first cookie matched
>>      idle CPU instead of the first idle CPU.
>>
>>  - Find cookie matched idlest CPU
>>      In the slow path of task wakeup, find the idlest CPU whose core
>>      cookie matches with task's cookie
>>
>>  - Don't migrate task if cookie not match
>>      For the NUMA load balance, don't migrate task to the CPU whose
>>      core cookie does not match with task's cookie
>>
>> Tested-by: Julien Desfossez <jdesfossez@xxxxxxxxxxxxxxxx>
>> Signed-off-by: Aubrey Li <aubrey.li@xxxxxxxxxxxxxxx>
>> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
>> Signed-off-by: Vineeth Remanan Pillai <viremana@xxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
>> ---
>>  kernel/sched/fair.c  | 64 ++++++++++++++++++++++++++++++++++++++++----
>>  kernel/sched/sched.h | 29 ++++++++++++++++++++
>>  2 files changed, 88 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index de82f88ba98c..ceb3906c9a8a 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1921,6 +1921,15 @@ static void task_numa_find_cpu(struct task_numa_env *env,
>>                 if (!cpumask_test_cpu(cpu, env->p->cpus_ptr))
>>                         continue;
>>
>> +#ifdef CONFIG_SCHED_CORE
>> +               /*
>> +                * Skip this cpu if source task's cookie does not match
>> +                * with CPU's core cookie.
>> +                */
>> +               if (!sched_core_cookie_match(cpu_rq(cpu), env->p))
>> +                       continue;
>> +#endif
>> +
>>                 env->dst_cpu = cpu;
>>                 if (task_numa_compare(env, taskimp, groupimp, maymove))
>>                         break;
>> @@ -5867,11 +5876,17 @@ find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this
>>
>>         /* Traverse only the allowed CPUs */
>>         for_each_cpu_and(i, sched_group_span(group), p->cpus_ptr) {
>> +               struct rq *rq = cpu_rq(i);
>> +
>> +#ifdef CONFIG_SCHED_CORE
>> +               if (!sched_core_cookie_match(rq, p))
>> +                       continue;
>> +#endif
>> +
>>                 if (sched_idle_cpu(i))
>>                         return i;
>>
>>                 if (available_idle_cpu(i)) {
>> -                       struct rq *rq = cpu_rq(i);
>>                         struct cpuidle_state *idle = idle_get_state(rq);
>>                         if (idle && idle->exit_latency < min_exit_latency) {
>>                                 /*
>> @@ -6129,8 +6144,18 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>>         for_each_cpu_wrap(cpu, cpus, target) {
>>                 if (!--nr)
>>                         return -1;
>> -               if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
>> -                       break;
>> +
>> +               if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) {
>> +#ifdef CONFIG_SCHED_CORE
>> +                       /*
>> +                        * If Core Scheduling is enabled, select this cpu
>> +                        * only if the process cookie matches core cookie.
>> +                        */
>> +                       if (sched_core_enabled(cpu_rq(cpu)) &&
>> +                           p->core_cookie == cpu_rq(cpu)->core->core_cookie)
>> +#endif
>> +                               break;
>> +               }
> 
> This makes code unreadable.
> Put this coresched specific stuff in an inline function; You can have
> a look at what is done with asym_fits_capacity()
> 
This is done in a refined version. Sorry I pasted the version embedded in this thread,
this is not the latest version.

>>         }
>>
>>         time = cpu_clock(this) - time;
>> @@ -7530,8 +7555,9 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>>          * We do not migrate tasks that are:
>>          * 1) throttled_lb_pair, or
>>          * 2) cannot be migrated to this CPU due to cpus_ptr, or
>> -        * 3) running (obviously), or
>> -        * 4) are cache-hot on their current CPU.
>> +        * 3) task's cookie does not match with this CPU's core cookie
>> +        * 4) running (obviously), or
>> +        * 5) are cache-hot on their current CPU.
>>          */
>>         if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>>                 return 0;
>> @@ -7566,6 +7592,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>>                 return 0;
>>         }
>>
>> +#ifdef CONFIG_SCHED_CORE
>> +       /*
>> +        * Don't migrate task if the task's cookie does not match
>> +        * with the destination CPU's core cookie.
>> +        */
>> +       if (!sched_core_cookie_match(cpu_rq(env->dst_cpu), p))
>> +               return 0;
>> +#endif
>> +
>>         /* Record that we found atleast one task that could run on dst_cpu */
>>         env->flags &= ~LBF_ALL_PINNED;
>>
>> @@ -8792,6 +8827,25 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
>>                                         p->cpus_ptr))
>>                         continue;
>>
>> +#ifdef CONFIG_SCHED_CORE
>> +               if (sched_core_enabled(cpu_rq(this_cpu))) {
>> +                       int i = 0;
>> +                       bool cookie_match = false;
>> +
>> +                       for_each_cpu(i, sched_group_span(group)) {
>> +                               struct rq *rq = cpu_rq(i);
>> +
>> +                               if (sched_core_cookie_match(rq, p)) {
>> +                                       cookie_match = true;
>> +                                       break;
>> +                               }
>> +                       }
>> +                       /* Skip over this group if no cookie matched */
>> +                       if (!cookie_match)
>> +                               continue;
>> +               }
>> +#endif
> 
> same here, encapsulate this to keep find_idlest_group readable
> 
Okay, I'll try to refine this.

Thanks,
-Aubrey