From: Valentin Schneider <valentin.schneider@arm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, peterz@infradead.org,
vincent.guittot@linaro.org, morten.rasmussen@arm.com,
Dietmar.Eggemann@arm.com
Subject: [PATCH v2 2/3] sched/fair: Tune down misfit nohz kicks
Date: Mon, 11 Feb 2019 17:59:45 +0000 [thread overview]
Message-ID: <20190211175946.4961-3-valentin.schneider@arm.com> (raw)
In-Reply-To: <20190211175946.4961-1-valentin.schneider@arm.com>
In
commmit 3b1baa6496e6 ("sched/fair: Add 'group_misfit_task' load-balance type")
we set rq->misfit_task_load whenever the current running task has a
utilization greater than 80% of rq->cpu_capacity. A non-zero value in
this field enables misfit load balancing.
However, if the task being looked at is already running on a CPU of
highest capacity, there's nothing more we can do for it. We can
currently spot this in update_sd_pick_busiest(), which prevents us
from selecting a sched_group of group_type == group_misfit_task as the
busiest group, but we don't do any of that in nohz_balancer_kick().
This means that we could repeatedly kick nohz CPUs when there's no
improvements in terms of load balance to be done.
Introduce a check_misfit_status() helper that returns true iff there
is a CPU in the system that could give more CPU capacity to a rq's
misfit task - IOW, there exists a CPU of higher capacity_orig or the
rq's CPU is severely pressured by rt/IRQ.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
kernel/sched/fair.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0f32e9830ec3..f9f11e140ba3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8058,6 +8058,18 @@ check_cpu_capacity(struct rq *rq, struct sched_domain *sd)
(rq->cpu_capacity_orig * 100));
}
+/*
+ * Check whether a rq has a misfit task and if it looks like we can actually
+ * help that task: we can migrate the task to a CPU of higher capacity, or
+ * the task's current CPU is heavily pressured.
+ */
+static inline int check_misfit_status(struct rq *rq, struct sched_domain *sd)
+{
+ return rq->misfit_task_load &&
+ (rq->cpu_capacity_orig < rq->rd->max_cpu_capacity ||
+ check_cpu_capacity(rq, sd));
+}
+
/*
* Group imbalance indicates (and tries to solve) the problem where balancing
* groups is inadequate due to ->cpus_allowed constraints.
@@ -9585,7 +9597,7 @@ static noinline void nohz_balancer_kick(struct rq *rq)
if (time_before(now, nohz.next_balance))
goto out;
- if (rq->nr_running >= 2 || rq->misfit_task_load) {
+ if (rq->nr_running >= 2) {
flags = NOHZ_KICK_MASK;
goto out;
}
@@ -9623,6 +9635,18 @@ static noinline void nohz_balancer_kick(struct rq *rq)
}
}
+ sd = rcu_dereference(per_cpu(sd_asym_cpucapacity, cpu));
+ if (sd) {
+ /*
+ * When ASYM_CPUCAPACITY; see if there's a higher capacity CPU
+ * to run the misfit task on.
+ */
+ if (check_misfit_status(rq, sd)) {
+ flags = NOHZ_KICK_MASK;
+ goto unlock;
+ }
+ }
+
sd = rcu_dereference(per_cpu(sd_asym_packing, cpu));
if (sd) {
/*
--
2.20.1
next prev parent reply other threads:[~2019-02-11 18:00 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-11 17:59 [PATCH v2 0/3] sched/fair: NOHZ cleanups and misfit improvement Valentin Schneider
2019-02-11 17:59 ` [PATCH v2 1/3] sched/fair: Comment some nohz_balancer_kick() kick conditions Valentin Schneider
2019-03-09 14:36 ` [tip:sched/urgent] " tip-bot for Valentin Schneider
2019-03-19 11:12 ` tip-bot for Valentin Schneider
2019-02-11 17:59 ` Valentin Schneider [this message]
2019-03-09 14:37 ` [tip:sched/urgent] sched/fair: Tune down misfit NOHZ kicks tip-bot for Valentin Schneider
2019-03-19 11:13 ` tip-bot for Valentin Schneider
2019-02-11 17:59 ` [PATCH v2 3/3] sched/fair: Skip LLC nohz logic for asymmetric systems Valentin Schneider
2019-03-09 14:38 ` [tip:sched/urgent] sched/fair: Skip LLC NOHZ " tip-bot for Valentin Schneider
2019-03-19 11:13 ` tip-bot for Valentin Schneider
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