linux-kernel - [PATCH v3] cpufreq: schedutil: rate limits for SCHED

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Date:   Thu,  8 Mar 2018 11:29:10 +0100
From:   Claudio Scordino <claudio@...dence.eu.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Cc:     Claudio Scordino <claudio@...dence.eu.com>,
        Ingo Molnar <mingo@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] cpufreq: schedutil: rate limits for SCHED_DEADLINE

When the SCHED_DEADLINE scheduling class increases the CPU utilization,
we should not wait for the rate limit, otherwise we may miss some
deadline.

Tests using rt-app on Exynos5422 with up to 10 SCHED_DEADLINE tasks have
shown reductions of even 10% of deadline misses with a negligible
increase of energy consumption (measured through Baylibre Cape).

Signed-off-by: Claudio Scordino <claudio@...dence.eu.com>
CC: Ingo Molnar <mingo@...hat.com>
CC: Patrick Bellasi <patrick.bellasi@....com>
CC: Dietmar Eggemann <dietmar.eggemann@....com>
CC: Morten Rasmussen <morten.rasmussen@....com>
CC: Juri Lelli <juri.lelli@...hat.com>
CC: Viresh Kumar <viresh.kumar@...aro.org>
CC: Vincent Guittot <vincent.guittot@...aro.org>
CC: Todd Kjos <tkjos@...roid.com>
CC: Joel Fernandes <joelaf@...gle.com>
CC: linux-pm@...r.kernel.org
CC: linux-kernel@...r.kernel.org
---
Changes from v2:
 - Rate limit ignored also in case of "fast switch"
 - Specific routine added
---
Changes from v1:
 - Logic moved from sugov_should_update_freq() to
   sugov_update_single()/_shared() to not duplicate data structures
 - Rate limit not ignored in case of "fast switch"
---
 kernel/sched/cpufreq_schedutil.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 7936f54..13f9cce 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -260,6 +260,17 @@ static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
 static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
 #endif /* CONFIG_NO_HZ_COMMON */
 
+/*
+ * Make sugov_should_update_freq() ignore the rate limit when DL
+ * has increased the utilization.
+ */
+static inline
+void set_dl_rate_limit(struct sugov_cpu *sg_cpu, struct sugov_policy *sg_policy)
+{
+	if (cpu_util_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->util_dl)
+		sg_policy->need_freq_update = true;
+}
+
 static void sugov_update_single(struct update_util_data *hook, u64 time,
 				unsigned int flags)
 {
@@ -273,6 +284,8 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 	sugov_set_iowait_boost(sg_cpu, time);
 	sg_cpu->last_update = time;
 
+	set_dl_rate_limit(sg_cpu, sg_policy);
+
 	if (!sugov_should_update_freq(sg_policy, time))
 		return;
 
@@ -354,6 +367,8 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
 
 	raw_spin_lock(&sg_policy->update_lock);
 
+	set_dl_rate_limit(sg_cpu, sg_policy);
+
 	sugov_get_util(sg_cpu);
 	sg_cpu->flags = flags;
 
-- 
2.7.4