From: Quentin Perret <quentin.perret@arm.com>
To: peterz@infradead.org, rjw@rjwysocki.net,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Cc: gregkh@linuxfoundation.org, mingo@redhat.com,
dietmar.eggemann@arm.com, morten.rasmussen@arm.com,
chris.redpath@arm.com, patrick.bellasi@arm.com,
valentin.schneider@arm.com, vincent.guittot@linaro.org,
thara.gopinath@linaro.org, viresh.kumar@linaro.org,
tkjos@google.com, joel@joelfernandes.org, smuckle@google.com,
adharmap@quicinc.com, skannan@quicinc.com,
pkondeti@codeaurora.org, juri.lelli@redhat.com,
edubezval@gmail.com, srinivas.pandruvada@linux.intel.com,
currojerez@riseup.net, javi.merino@kernel.org,
quentin.perret@arm.com
Subject: [RFC PATCH v4 08/12] sched: Add over-utilization/tipping point indicator
Date: Thu, 28 Jun 2018 12:40:39 +0100 [thread overview]
Message-ID: <20180628114043.24724-9-quentin.perret@arm.com> (raw)
In-Reply-To: <20180628114043.24724-1-quentin.perret@arm.com>
From: Morten Rasmussen <morten.rasmussen@arm.com>
Energy-aware scheduling is only meant to be active while the system is
_not_ over-utilized. That is, there are spare cycles available to shift
tasks around based on their actual utilization to get a more
energy-efficient task distribution without depriving any tasks. When
above the tipping point task placement is done the traditional way based
on load_avg, spreading the tasks across as many cpus as possible based
on priority scaled load to preserve smp_nice. Below the tipping point we
want to use util_avg instead. We need to define a criteria for when we
make the switch.
The util_avg for each cpu converges towards 100% (1024) regardless of
how many task additional task we may put on it. If we define
over-utilized as:
sum_{cpus}(rq.cfs.avg.util_avg) + margin > sum_{cpus}(rq.capacity)
some individual cpus may be over-utilized running multiple tasks even
when the above condition is false. That should be okay as long as we try
to spread the tasks out to avoid per-cpu over-utilization as much as
possible and if all tasks have the _same_ priority. If the latter isn't
true, we have to consider priority to preserve smp_nice.
For example, we could have n_cpus nice=-10 util_avg=55% tasks and
n_cpus/2 nice=0 util_avg=60% tasks. Balancing based on util_avg we are
likely to end up with nice=-10 tasks sharing cpus and nice=0 tasks
getting their own as we 1.5*n_cpus tasks in total and 55%+55% is less
over-utilized than 55%+60% for those cpus that have to be shared. The
system utilization is only 85% of the system capacity, but we are
breaking smp_nice.
To be sure not to break smp_nice, we have defined over-utilization
conservatively as when any cpu in the system is fully utilized at it's
highest frequency instead:
cpu_rq(any).cfs.avg.util_avg + margin > cpu_rq(any).capacity
IOW, as soon as one cpu is (nearly) 100% utilized, we switch to load_avg
to factor in priority to preserve smp_nice.
With this definition, we can skip periodic load-balance as no cpu has an
always-running task when the system is not over-utilized. All tasks will
be periodic and we can balance them at wake-up. This conservative
condition does however mean that some scenarios that could benefit from
energy-aware decisions even if one cpu is fully utilized would not get
those benefits.
For system where some cpus might have reduced capacity on some cpus
(RT-pressure and/or big.LITTLE), we want periodic load-balance checks as
soon a just a single cpu is fully utilized as it might one of those with
reduced capacity and in that case we want to migrate it.
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
---
kernel/sched/fair.c | 48 +++++++++++++++++++++++++++++++++++++++++---
kernel/sched/sched.h | 3 +++
2 files changed, 48 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e497c05aab7f..4f74c6d0a79e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5374,6 +5374,24 @@ static inline void hrtick_update(struct rq *rq)
}
#endif
+#ifdef CONFIG_SMP
+static inline unsigned long cpu_util(int cpu);
+static unsigned long capacity_of(int cpu);
+
+static inline bool cpu_overutilized(int cpu)
+{
+ return (capacity_of(cpu) * 1024) < (cpu_util(cpu) * capacity_margin);
+}
+
+static inline void update_overutilized_status(struct rq *rq)
+{
+ if (!READ_ONCE(rq->rd->overutilized) && cpu_overutilized(rq->cpu))
+ WRITE_ONCE(rq->rd->overutilized, 1);
+}
+#else
+static inline void update_overutilized_status(struct rq *rq) { }
+#endif
+
/*
* The enqueue_task method is called before nr_running is
* increased. Here we update the fair scheduling stats and
@@ -5384,6 +5402,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
struct cfs_rq *cfs_rq;
struct sched_entity *se = &p->se;
+ int task_new = !(flags & ENQUEUE_WAKEUP);
/*
* The code below (indirectly) updates schedutil which looks at
@@ -5431,8 +5450,12 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
update_cfs_group(se);
}
- if (!se)
+ if (!se) {
add_nr_running(rq, 1);
+ if (!task_new)
+ update_overutilized_status(rq);
+
+ }
hrtick_update(rq);
}
@@ -8114,11 +8137,12 @@ static bool update_nohz_stats(struct rq *rq, bool force)
* @local_group: Does group contain this_cpu.
* @sgs: variable to hold the statistics for this group.
* @overload: Indicate more than one runnable task for any CPU.
+ * @overutilized: Indicate overutilization for any CPU.
*/
static inline void update_sg_lb_stats(struct lb_env *env,
struct sched_group *group, int load_idx,
int local_group, struct sg_lb_stats *sgs,
- bool *overload)
+ bool *overload, int *overutilized)
{
unsigned long load;
int i, nr_running;
@@ -8145,6 +8169,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
if (nr_running > 1)
*overload = true;
+ if (cpu_overutilized(i))
+ *overutilized = 1;
+
#ifdef CONFIG_NUMA_BALANCING
sgs->nr_numa_running += rq->nr_numa_running;
sgs->nr_preferred_running += rq->nr_preferred_running;
@@ -8282,6 +8309,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
struct sg_lb_stats tmp_sgs;
int load_idx, prefer_sibling = 0;
bool overload = false;
+ int overutilized = 0;
if (child && child->flags & SD_PREFER_SIBLING)
prefer_sibling = 1;
@@ -8308,7 +8336,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
}
update_sg_lb_stats(env, sg, load_idx, local_group, sgs,
- &overload);
+ &overload, &overutilized);
if (local_group)
goto next_group;
@@ -8360,6 +8388,13 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
/* update overload indicator if we are at root domain */
if (env->dst_rq->rd->overload != overload)
env->dst_rq->rd->overload = overload;
+
+ /* Update over-utilization (tipping point, U >= 0) indicator */
+ if (READ_ONCE(env->dst_rq->rd->overutilized) != overutilized)
+ WRITE_ONCE(env->dst_rq->rd->overutilized, overutilized);
+ } else {
+ if (!READ_ONCE(env->dst_rq->rd->overutilized) && overutilized)
+ WRITE_ONCE(env->dst_rq->rd->overutilized, 1);
}
}
@@ -8579,6 +8614,11 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
* this level.
*/
update_sd_lb_stats(env, &sds);
+
+ if (rd_freq_domain(env->dst_rq->rd) &&
+ !READ_ONCE(env->dst_rq->rd->overutilized))
+ goto out_balanced;
+
local = &sds.local_stat;
busiest = &sds.busiest_stat;
@@ -9936,6 +9976,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
if (static_branch_unlikely(&sched_numa_balancing))
task_tick_numa(rq, curr);
+
+ update_overutilized_status(task_rq(curr));
}
/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 5d4e9bbe9e53..4e6548e4afc5 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -698,6 +698,9 @@ struct root_domain {
/* Indicate more than one runnable task for any CPU */
bool overload;
+ /* Indicate one or more cpus over-utilized (tipping point) */
+ int overutilized;
+
/*
* The bit corresponding to a CPU gets set here if such CPU has more
* than one runnable -deadline task (as it is below for RT tasks).
--
2.17.1
next prev parent reply other threads:[~2018-06-28 11:41 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-28 11:40 [RFC PATCH v4 00/12] Energy Aware Scheduling Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 01/12] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 02/12] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 03/12] PM: Introduce an Energy Model management framework Quentin Perret
2018-07-05 14:31 ` Peter Zijlstra
2018-07-05 15:24 ` Quentin Perret
2018-07-05 14:39 ` Peter Zijlstra
2018-07-05 15:09 ` Quentin Perret
2018-07-05 15:06 ` Peter Zijlstra
2018-07-05 15:32 ` Quentin Perret
2018-07-06 9:57 ` Vincent Guittot
2018-07-06 10:03 ` Peter Zijlstra
2018-07-06 10:06 ` Quentin Perret
2018-07-06 10:05 ` Quentin Perret
2018-07-09 18:07 ` Dietmar Eggemann
2018-07-10 8:32 ` Quentin Perret
2018-07-16 10:29 ` Quentin Perret
2018-07-17 8:57 ` Dietmar Eggemann
2018-07-17 14:19 ` Quentin Perret
2018-07-17 16:00 ` Dietmar Eggemann
2018-06-28 11:40 ` [RFC PATCH v4 04/12] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 05/12] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-07-05 17:29 ` Peter Zijlstra
2018-07-05 17:48 ` Quentin Perret
2018-07-05 17:33 ` Peter Zijlstra
2018-07-05 17:50 ` Quentin Perret
2018-07-05 18:14 ` Peter Zijlstra
2018-06-28 11:40 ` [RFC PATCH v4 06/12] sched/topology: Lowest energy aware balancing sched_domain level pointer Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 07/12] sched/topology: Introduce sched_energy_present static key Quentin Perret
2018-06-28 11:40 ` Quentin Perret [this message]
2018-07-06 11:32 ` [RFC PATCH v4 08/12] sched: Add over-utilization/tipping point indicator Peter Zijlstra
2018-07-06 13:20 ` Quentin Perret
2018-07-06 13:24 ` Peter Zijlstra
2018-07-06 13:40 ` Quentin Perret
2018-07-06 11:39 ` Peter Zijlstra
2018-07-06 11:41 ` Peter Zijlstra
2018-07-06 11:49 ` Valentin Schneider
2018-06-28 11:40 ` [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-07-06 13:12 ` Peter Zijlstra
2018-07-06 15:12 ` Quentin Perret
2018-07-06 15:49 ` Peter Zijlstra
2018-07-06 17:04 ` Quentin Perret
2018-07-09 12:01 ` Peter Zijlstra
2018-07-09 15:28 ` Quentin Perret
2018-07-09 15:42 ` Peter Zijlstra
2018-07-09 16:07 ` Quentin Perret
2018-07-06 15:50 ` Peter Zijlstra
2018-06-28 11:40 ` [RFC PATCH v4 10/12] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 11/12] OPTIONAL: arch_topology: Start Energy Aware Scheduling Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 12/12] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret
2018-07-06 10:10 ` Vincent Guittot
2018-07-06 10:18 ` Quentin Perret
2018-07-30 15:53 ` Vincent Guittot
2018-07-30 16:20 ` Quentin Perret
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