Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [RFC PATCH 5/6] sched/fair: trigger the update of blocked load on newly idle cpu | Date | Tue, 09 Feb 2021 13:09:41 +0000 |
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On 05/02/21 12:48, Vincent Guittot wrote: > Instead of waking up a random and already idle CPU, we can take advantage > of this_cpu being about to enter idle to run the ILB and update the > blocked load. > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > include/linux/sched/nohz.h | 2 ++ > kernel/sched/fair.c | 11 ++++++++--- > kernel/sched/idle.c | 6 ++++++ > 3 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/include/linux/sched/nohz.h b/include/linux/sched/nohz.h > index 6d67e9a5af6b..74cdc4e87310 100644 > --- a/include/linux/sched/nohz.h > +++ b/include/linux/sched/nohz.h > @@ -9,8 +9,10 @@ > #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON) > extern void nohz_balance_enter_idle(int cpu); > extern int get_nohz_timer_target(void); > +extern void nohz_run_idle_balance(int cpu); > #else > static inline void nohz_balance_enter_idle(int cpu) { } > +static inline void nohz_run_idle_balance(int cpu) { } > #endif > > #ifdef CONFIG_NO_HZ_COMMON > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 935594cd5430..3d2ab28d5736 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10461,6 +10461,11 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) > return true; > } > > +void nohz_run_idle_balance(int cpu) > +{ > + nohz_idle_balance(cpu_rq(cpu), CPU_IDLE); > +} > + > static void nohz_newidle_balance(struct rq *this_rq) > { > int this_cpu = this_rq->cpu; > @@ -10482,10 +10487,10 @@ static void nohz_newidle_balance(struct rq *this_rq) > return; > > /* > - * Blocked load of idle CPUs need to be updated. > - * Kick an ILB to update statistics. > + * Set the need to trigger ILB in order to update blocked load > + * before entering idle state. > */ > - kick_ilb(NOHZ_STATS_KICK); > + this_rq->nohz_idle_balance = NOHZ_STATS_KICK; > } > > #else /* !CONFIG_NO_HZ_COMMON */ > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index 305727ea0677..52a4e9ce2f9b 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -261,6 +261,12 @@ static void cpuidle_idle_call(void) > static void do_idle(void) > { > int cpu = smp_processor_id(); > + > + /* > + * Check if we need to update some blocked load > + */ > + nohz_run_idle_balance(cpu); > +
What do we gain from doing this here vs having a stats update in newidle_balance()?
The current approach is to have a combined load_balance() + blocked load update during newidle, and I get that this can take too long. But then, we could still have what you're adding to do_idle() in the tail of newidle_balance() itself, no? i.e.
newidle_balance() ... for_each_domain(this_cpu, sd) { ... pulled_task = load_balance(...); ... } ... if (!pulled_task && !this_rq->nr_running) { this_rq->nohz_idle_balance = NOHZ_STATS_KICK; _nohz_idle_balance(); }
or somesuch.
> /* > * If the arch has a polling bit, we maintain an invariant: > * > -- > 2.17.1
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