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SubjectRe: [PATCH v3 0/4] scheduler-driven cpu frequency selection
Hi Mike,

I have tried to evaluate the performance and the power consumption of
the various policy that we have in the kernel to manage the DVFS of
cpus including your sched-dvfs proposal. For this purpose, i have used
rt-app and a script that are available here:
https://git.linaro.org/power/rt-app.git/shortlog/refs/heads/master.
The script is in the directory:
doc/examples/cpufreq_governor_efficiency/
For evaluating the performance of DVFS policy, I use rt-app to run a
simple sequence that alternates run phase and sleep phase. The run
phase is done by looping a defined number of time on a function that
burns cycles (The number of loop is calibrated to be equivalent to a
specified duration at max frequency of the cpu). At the end of the
test, we know how many time is needed by each policy to run the same
pattern and we can compare policies. I have also done some power
consumption measurement so we can compare both the
performance/responsiveness and power consumption (the power figure
only reflects the power consumption of the A53 cluster).

The test has been done on cortex-A53 platofrm so i have ported the
frequency invariance patch [1/4] on arm64 (attached to the email for
reference)

The performance figures has been normalized; so 100% means as fast as
the performance governor that always use the max frequency and 0%
means as slow as the powersave governor that always uses the min
frequency. The power consumption figures have been normalized vs the
performance governor power consumption. For all governor i have used
the default parameters which means a sampling rate of 10ms and a
sampling_down_factor of 1 for ondemand and a sampling rate of 200ms
for conservative governor

performance powersave ondemand sched
conservative
run/sleep perf energy perf energy perf energy perf energy
perf energy
50ms/1000ms 100% 100% 0% 34% 95% 62% 49% 35% 72% 33%
100ms/1000ms 100% 100% 0% 41% 98% 78% 69% 41% 92% 45%
200ms/1000ms 100% 100% 0% 51% 98% 78% 86% 62% 93% 62%
400ms/1000ms 100% 100% 0% 55% 99% 83% 93% 63% 99% 77%
1000ms/100ms 100% 100% 0% 74% 99% 100% 96% 97% 99% 99%

We can see that the responsiveness of the sched governor is not that
good for short running duration but this can probably can be explained
with the responsiveness of the load tracking which needs around 75ms
to reach 80% of max usage. there are several proposal to add the
blocked tasks in the usage of a cpu, this can may be improved the
responsiveness for some pattern.

Regards,
Vincent

On 27 June 2015 at 01:53, Michael Turquette <mturquette@baylibre.com> wrote:
> This series addresses the comments from v2 and rearranges the code to
> separate the bits that are safe to merge from the bits that are not. In
> particular the simplified governor no longer implements any policy of
> its own. That code is migrated to fair.c and marked as RFC. The
> capacity-selection code in fair.c (patch #4) is a placeholder and can be
> replaced by something more sophisticated, and it illustrates the use of
> the new governor api's for anyone that wants to play around with
> crafting a new policy.
>
> Patch #1 is a re-post from Morten, as it is the only dependency these
> patches have on his EAS series. Please consider merging patches #2 and
> #3 if they do not appear too controversial. Without enabling the feature
> in Kconfig will be no impact on existing code.
>
> Michael Turquette (3):
> cpufreq: introduce cpufreq_driver_might_sleep
> sched: scheduler-driven cpu frequency selection
> [RFC] sched: cfs: cpu frequency scaling policy
>
> Morten Rasmussen (1):
> arm: Frequency invariant scheduler load-tracking support
>
> arch/arm/include/asm/topology.h | 7 +
> arch/arm/kernel/smp.c | 53 ++++++-
> arch/arm/kernel/topology.c | 17 +++
> drivers/cpufreq/Kconfig | 24 ++++
> drivers/cpufreq/cpufreq.c | 6 +
> include/linux/cpufreq.h | 12 ++
> kernel/sched/Makefile | 1 +
> kernel/sched/cpufreq_sched.c | 308 ++++++++++++++++++++++++++++++++++++++++
> kernel/sched/fair.c | 41 ++++++
> kernel/sched/sched.h | 8 ++
> 10 files changed, 475 insertions(+), 2 deletions(-)
> create mode 100644 kernel/sched/cpufreq_sched.c
>
> --
> 1.9.1
>
From 1be4a1e126cdb1b47b4d8a5dd156f8bca04715c0 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Fri, 3 Jul 2015 10:02:53 +0200
Subject: [PATCH] arm64: Frequency invariant scheduler load-tracking support

Implements arch-specific function to provide the scheduler with a
frequency scaling correction factor for more accurate load-tracking.

This patch is based on the implementation that has been done for arm arch
by Morten Rasmussen <morten.rasmussen@arm.com>

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
arch/arm64/include/asm/topology.h | 11 ++++++
arch/arm64/kernel/smp.c | 80 +++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/topology.c | 19 ++++++++++
3 files changed, 110 insertions(+)

diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
index 7ebcd31..887835a 100644
--- a/arch/arm64/include/asm/topology.h
+++ b/arch/arm64/include/asm/topology.h
@@ -24,6 +24,17 @@ void init_cpu_topology(void);
void store_cpu_topology(unsigned int cpuid);
const struct cpumask *cpu_coregroup_mask(int cpu);

+#ifdef CONFIG_CPU_FREQ
+
+#define arch_scale_freq_capacity arm64_arch_scale_freq_capacity
+struct sched_domain;
+extern unsigned long arm64_arch_scale_freq_capacity(struct sched_domain *sd,
+ int cpu);
+
+DECLARE_PER_CPU(atomic_long_t, cpu_freq_capacity);
+
+#endif /* CONFIG_CPU_FREQ */
+
#else

static inline void init_cpu_topology(void) { }
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 328b8ce..45b88cb 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -34,6 +34,7 @@
#include <linux/percpu.h>
#include <linux/clockchips.h>
#include <linux/completion.h>
+#include <linux/cpufreq.h>
#include <linux/of.h>
#include <linux/irq_work.h>

@@ -656,3 +657,82 @@ int setup_profiling_timer(unsigned int multiplier)
{
return -EINVAL;
}
+
+#ifdef CONFIG_CPU_FREQ
+
+static DEFINE_PER_CPU(atomic_long_t, cpu_max_freq);
+DEFINE_PER_CPU(atomic_long_t, cpu_freq_capacity);
+
+/*
+ * Scheduler load-tracking scale-invariance
+ *
+ * Provides the scheduler with a scale-invariance correction factor that
+ * compensates for frequency scaling through arch_scale_freq_capacity()
+ * (implemented in topology.c).
+ */
+static inline
+void scale_freq_capacity(int cpu, unsigned long curr, unsigned long max)
+{
+ unsigned long capacity;
+
+ if (!max)
+ return;
+
+ capacity = (curr << SCHED_CAPACITY_SHIFT) / max;
+ atomic_long_set(&per_cpu(cpu_freq_capacity, cpu), capacity);
+}
+
+static int cpufreq_callback(struct notifier_block *nb,
+ unsigned long val, void *data)
+{
+ struct cpufreq_freqs *freq = data;
+ int cpu = freq->cpu;
+ unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu));
+
+ if (freq->flags & CPUFREQ_CONST_LOOPS)
+ return NOTIFY_OK;
+
+ scale_freq_capacity(cpu, freq->new, max);
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block cpufreq_notifier = {
+ .notifier_call = cpufreq_callback,
+};
+
+static int cpufreq_policy_callback(struct notifier_block *nb,
+ unsigned long val, void *data)
+{
+ struct cpufreq_policy *policy = data;
+ int i;
+
+ if (val != CPUFREQ_NOTIFY)
+ return NOTIFY_OK;
+
+ for_each_cpu(i, policy->cpus) {
+ scale_freq_capacity(i, policy->cur, policy->max);
+ atomic_long_set(&per_cpu(cpu_max_freq, i), policy->max);
+ }
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block cpufreq_policy_notifier = {
+ .notifier_call = cpufreq_policy_callback,
+};
+
+static int __init register_cpufreq_notifier(void)
+{
+ int ret;
+
+ ret = cpufreq_register_notifier(&cpufreq_notifier,
+ CPUFREQ_TRANSITION_NOTIFIER);
+ if (ret)
+ return ret;
+
+ return cpufreq_register_notifier(&cpufreq_policy_notifier,
+ CPUFREQ_POLICY_NOTIFIER);
+}
+core_initcall(register_cpufreq_notifier);
+#endif
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index fcb8f7b..6387f65 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -200,6 +200,25 @@ static int __init parse_dt_topology(void)
return ret;
}

+#ifdef CONFIG_CPU_FREQ
+/*
+ * Scheduler load-tracking scale-invariance
+ *
+ * Provides the scheduler with a scale-invariance correction factor that
+ * compensates for frequency scaling (arch_scale_freq_capacity()). The scaling
+ * factor is updated in smp.c
+ */
+unsigned long arm64_arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
+{
+ unsigned long curr = atomic_long_read(&per_cpu(cpu_freq_capacity, cpu));
+
+ if (!curr)
+ return SCHED_CAPACITY_SCALE;
+
+ return curr;
+}
+#endif
+
/*
* cpu topology table
*/
--
1.9.1
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