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Subject[PATCH v3] cpufreq: schedutil: rate limits for SCHED_DEADLINE
Date
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@evidence.eu.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: Patrick Bellasi <patrick.bellasi@arm.com>
CC: Dietmar Eggemann <dietmar.eggemann@arm.com>
CC: Morten Rasmussen <morten.rasmussen@arm.com>
CC: Juri Lelli <juri.lelli@redhat.com>
CC: Viresh Kumar <viresh.kumar@linaro.org>
CC: Vincent Guittot <vincent.guittot@linaro.org>
CC: Todd Kjos <tkjos@android.com>
CC: Joel Fernandes <joelaf@google.com>
CC: linux-pm@vger.kernel.org
CC: linux-kernel@vger.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
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