Re: [RFC PATCH 4/4] sched/core: Do numa balance in cfs_migration

[Yafang Shao <laoar.shao@gmail.com>]

On Sat, Nov 6, 2021 at 1:02 AM Valentin Schneider
<valentin.schneider@arm.com> wrote:
>
> On 04/11/21 14:57, Yafang Shao wrote:
> > Similar to active load balance, the numa balance work is also applied to
> > cfs tasks only and it should't preempt other FIFO tasks. We'd better assign
> > cfs_migration to the numa balance as well.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > Cc: Valentin Schneider <valentin.schneider@arm.com>
> > Cc: Vincent Guittot <vincent.guittot@linaro.org>
> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > ---
> >  kernel/sched/core.c  |  2 +-
> >  kernel/sched/fair.c  | 13 +++++++++++++
> >  kernel/sched/sched.h |  2 ++
> >  3 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9cb81ef8acc8..4a37b06715f4 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -8724,7 +8724,7 @@ int migrate_task_to(struct task_struct *p, int target_cpu)
> >       /* TODO: This is not properly updating schedstats */
> >
> >       trace_sched_move_numa(p, curr_cpu, target_cpu);
> > -     return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
> > +     return wakeup_cfs_migrater(curr_cpu, migration_cpu_stop, &arg);
>
> So that one I find really icky - migration_cpu_stop() really is meant to be
> run from a CPU stopper (cf. cpu_stop suffix). IMO this is the opportunity
> to make NUMA balancing reuse the logic for CFS active balance here, but per
> previous email I'd say it could be done as a second step.
>

Sure.

> >  }
> >
> >  /*
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 932f63baeb82..b7a155e05c98 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -11960,6 +11960,19 @@ static void wakeup_cfs_migrater_nowait(unsigned int cpu, cpu_stop_fn_t fn, void
> >       cfs_migration_queue_work(cpu, work_buf);
> >  }
> >
> > +bool wakeup_cfs_migrater(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
> > +{
> > +     struct cpu_stop_done done;
> > +     struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done, .caller = _RET_IP_ };
> > +
> > +     cpu_stop_init_done(&done, 1);
> > +     cfs_migration_queue_work(cpu, &work);
> > +     cond_resched();
> > +     wait_for_completion(&done.completion);
> > +
> > +     return done.ret;
> > +}
> > +
> >  static int cfs_migration_should_run(unsigned int cpu)
> >  {
> >       struct cfs_migrater *migrater = &per_cpu(cfs_migrater, cpu);
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index a00fc7057d97..7b242c18a6d8 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -3055,6 +3055,8 @@ static inline bool is_per_cpu_kthread(struct task_struct *p)
> >
> >       return true;
> >  }
> > +
> > +bool wakeup_cfs_migrater(unsigned int cpu, cpu_stop_fn_t fn, void *arg);
> >  #endif
> >
> >  extern void swake_up_all_locked(struct swait_queue_head *q);
> > --
> > 2.17.1



-- 
Thanks
Yafang