On Tue, 2020-04-28 at 22:37 +0100, Valentin Schneider wrote:
> On 28/04/20 06:02, Scott Wood wrote:
> > Thus, newidle_balance() is entered with interrupts enabled, which allows
> > (in the next patch) enabling interrupts when the lock is dropped.
> >
> > Signed-off-by: Scott Wood <swood@xxxxxxxxxx>
> > ---
> > kernel/sched/core.c | 7 ++++---
> > kernel/sched/fair.c | 45 ++++++++++++++++----------------------------
> > kernel/sched/sched.h | 6 ++----
> > 3 files changed, 22 insertions(+), 36 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9a2fbf98fd6f..0294beb8d16c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3241,6 +3241,10 @@ static struct rq *finish_task_switch(struct
> > task_struct *prev)
> > }
> >
> > tick_nohz_task_switch();
> > +
> > + if (is_idle_task(current))
> > + newidle_balance();
> > +
>
> This means we must go through a switch_to(idle) before figuring out we
> could've switched to a CFS task, and do it then. I'm curious to see the
> performance impact of that.
Any particular benchmark I should try?
> > return rq;
> > }
> >
> > @@ -10425,14 +10408,23 @@ static inline void nohz_newidle_balance(struct
> > rq *this_rq) { }
> > * 0 - failed, no new tasks
> > * > 0 - success, new (fair) tasks present
> > */
> > -int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
> > +int newidle_balance(void)
> > {
> > unsigned long next_balance = jiffies + HZ;
> > - int this_cpu = this_rq->cpu;
> > + int this_cpu;
> > struct sched_domain *sd;
> > + struct rq *this_rq;
> > int pulled_task = 0;
> > u64 curr_cost = 0;
> >
> > + preempt_disable();
> > + this_rq = this_rq();
> > + this_cpu = this_rq->cpu;
> > + local_bh_disable();
> > + raw_spin_lock_irq(&this_rq->lock);
> > +
> > + update_rq_clock(this_rq);
> > +
> > update_misfit_status(NULL, this_rq);
>
> I'm thinking this should be moved to where newidle_balance() used to be,
> otherwise we have a window where the rq is flagged as having a misfit
> task despite not having any runnable CFS tasks.
OK
-Scott
