Messages in this thread |  | | From | Vincent Guittot <> | Date | Fri, 29 Oct 2021 14:19:07 +0200 | Subject | Re: [PATCH 3/5] sched/fair: Wait before decaying max_newidle_lb_cost |
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On Fri, 29 Oct 2021 at 12:01, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 19/10/2021 14:35, Vincent Guittot wrote: > > Decay max_newidle_lb_cost only when it has not been updated for a while > > and ensure to not decay a recently changed value. > > > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > --- > > include/linux/sched/topology.h | 2 +- > > kernel/sched/fair.c | 36 +++++++++++++++++++++++++--------- > > kernel/sched/topology.c | 2 +- > > 3 files changed, 29 insertions(+), 11 deletions(-) > > > > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > > index 2f9166f6dec8..c07bfa2d80f2 100644 > > --- a/include/linux/sched/topology.h > > +++ b/include/linux/sched/topology.h > > @@ -105,7 +105,7 @@ struct sched_domain { > > > > /* idle_balance() stats */ > > u64 max_newidle_lb_cost; > > - unsigned long next_decay_max_lb_cost; > > + unsigned long last_decay_max_lb_cost; > > > > u64 avg_scan_cost; /* select_idle_sibling */ > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index c4c36865321b..e50fd751e1df 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -10239,6 +10239,30 @@ void update_max_interval(void) > > max_load_balance_interval = HZ*num_online_cpus()/10; > > } > > > > +static inline bool update_newidle_cost(struct sched_domain *sd, u64 cost) > > +{ > > + if (cost > sd->max_newidle_lb_cost) { > > + /* > > + * Track max cost of a domain to make sure to not delay the > > + * next wakeup on the CPU. > > + */ > > + sd->max_newidle_lb_cost = cost; > > + sd->last_decay_max_lb_cost = jiffies; > > That's the actual change of the patch: sd->last_decay_max_lb_cost being > moved forward also when newidle cost is updated from newidle_balance() ? > > > + } else if (time_after(jiffies, sd->last_decay_max_lb_cost + HZ)) { > > + /* > > + * Decay the newidle max times by ~1% per second to ensure that > > + * it is not outdated and the current max cost is actually > > + * shorter. > > I assume that `max cost` refers here to a local variable of the only > caller of update_newidle_cost(..., 0) - rebalance_domains()? > > "the current max cost" has to be shorter so that > rq->max_idle_balance_cost also decays in this case. Is this what this > comment tries to say here?
I refer to the time tracked in sd->max_newidle_lb_cost here i set current_cost to zero to trigger a possible decay of sd->max_newidle_lb_cost
> > [...]
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