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Subject[PATCH v2 10/10] drivers base/arch_topology: inline cpu- and frequency-invariant accounting
Date
To speed up the cpu- and frequency-invariant accounting of the task
scheduler make sure that the CIE (topology_get_cpu_scale()) and FIE
(topology_get_freq_scale() get completely inlined into the task
scheduler consumer functions (e.g. __update_load_avg_se()).

This patch-set changes the interface for CIE and FIE from:

drivers/base/arch_topology.c:

static DEFINE_PER_CPU(unsigned long, item);

unsigned long topology_get_item_scale(...)
{
return per_cpu(item, cpu)
}

include/linux/arch_topology.h:

unsigned long topology_get_item_scale(...);

to:

drivers/base/arch_topology.c:

DEFINE_PER_CPU(unsigned long, item);

include/linux/arch_topology.h:

DECLARE_PER_CPU(unsigned long, item);

static inline
unsigned long topology_get_item_scale(...)
{
return per_cpu(item, cpu)
}

An uplift in performance could be detected running the kernel with the
following test patch on top (on JUNO R0 (arm64)):

@@ -2812,10 +2812,18 @@ accumulate_sum(u64 delta, int cpu, struct sched_avg *sa,
unsigned long scale_freq, scale_cpu;
u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
u64 periods;
+ u64 t1, t2;
+
+ t1 = sched_clock_cpu(cpu);

scale_freq = arch_scale_freq_capacity(NULL, cpu);
scale_cpu = arch_scale_cpu_capacity(NULL, cpu);

+ t2 = sched_clock_cpu(cpu);
+
+ trace_printk("cpu=%d t1=%llu t2=%llu diff=%llu\n",
+ cpu, t1, t2, t2 - t1);
+
delta += sa->period_contrib;
periods = delta / 1024; /* A period is * 1024us * (~1ms) */

The following test results (3 test runs each) have been obtained by
tracing this trace printk (diff=x) for Cortex A-53 (LITTLE) and Cortex
A-57 (big) cpus w/ (inline) and w/o (non-inline) this patch.

mean max min

A-57 inline:

119.6 300 60
96.8 280 60
110.2 660 60

A-57 non-inline:

142.8 460 80
157.6 680 80
153.4 720 80

A-53 inline:
141.6 360 100
118.8 500 100
148.6 380 100

A-53 non-inline:

293 840 120
253.2 840 120
299.6 1060 140

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
drivers/base/arch_topology.c | 14 ++------------
include/linux/arch_topology.h | 15 +++++++++++++--
2 files changed, 15 insertions(+), 14 deletions(-)
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 63fb3f945d21..b4481cff14bf 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -22,12 +22,7 @@
#include <linux/string.h>
#include <linux/sched/topology.h>

-static DEFINE_PER_CPU(unsigned long, freq_scale) = SCHED_CAPACITY_SCALE;
-
-unsigned long topology_get_freq_scale(struct sched_domain *sd, int cpu)
-{
- return per_cpu(freq_scale, cpu);
-}
+DEFINE_PER_CPU(unsigned long, freq_scale) = SCHED_CAPACITY_SCALE;

void topology_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
unsigned long max_freq)
@@ -43,12 +38,7 @@ void topology_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,


static DEFINE_MUTEX(cpu_scale_mutex);
-static DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
-
-unsigned long topology_get_cpu_scale(struct sched_domain *sd, int cpu)
-{
- return per_cpu(cpu_scale, cpu);
-}
+DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;

void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
{
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index 168104d2d2cf..361e85a30151 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -11,12 +11,23 @@ void topology_normalize_cpu_scale(void);
struct device_node;
int topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu);

+DECLARE_PER_CPU(unsigned long, cpu_scale);
+DECLARE_PER_CPU(unsigned long, freq_scale);
+
struct sched_domain;
-unsigned long topology_get_cpu_scale(struct sched_domain *sd, int cpu);
+static inline
+unsigned long topology_get_cpu_scale(struct sched_domain *sd, int cpu)
+{
+ return per_cpu(cpu_scale, cpu);
+}

void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity);

-unsigned long topology_get_freq_scale(struct sched_domain *sd, int cpu);
+static inline
+unsigned long topology_get_freq_scale(struct sched_domain *sd, int cpu)
+{
+ return per_cpu(freq_scale, cpu);
+}

void topology_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
unsigned long max_freq);
--
2.11.0
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