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SubjectRe: [PATCH v7 REPOST 9/9] arm64: add sysfs cpu_capacity attribute
Hi,

small update to be in sync with Russell's comments on arm correspoding
patch.

On 17/10/16 16:46, Juri Lelli wrote:
> Add a sysfs cpu_capacity attribute with which it is possible to read and
> write (thus over-writing default values) CPUs capacity. This might be
> useful in situations where values needs changing after boot.
>
> The new attribute shows up as:
>
> /sys/devices/system/cpu/cpu*/cpu_capacity
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Juri Lelli <juri.lelli@arm.com>
> ---
>
> Changes from v5:
> - add mutex to protect cpu_scale (as pointed out by Morten off-line)

--->8---
From 17684f3db6d74342da424997badcb3714a1a9e63 Mon Sep 17 00:00:00 2001
From: Juri Lelli <juri.lelli@arm.com>
Date: Wed, 14 Oct 2015 12:02:05 +0100
Subject: [PATCH v7.1 9/9] arm64: add sysfs cpu_capacity attribute

Add a sysfs cpu_capacity attribute with which it is possible to read and
write (thus over-writing default values) CPUs capacity. This might be
useful in situations where values needs changing after boot.

The new attribute shows up as:

/sys/devices/system/cpu/cpu*/cpu_capacity

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
---

Changes from v5:
- add mutex to protect cpu_scale (as pointed out by Morten off-line)

Changes from v7:
- include files moved at top of file
- show_cpu_capacity simplified to less lines of code
- unnecessary cast removed in store_cpu_capacity
- use DEVICE_ATTR_RW() instead of DEVICE_ATTR()
- use subsys_initcall instead of late_initcall
---
arch/arm64/kernel/topology.c | 64 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 64 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index b75b0ba2e113..23e9e13bd2aa 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -20,12 +20,15 @@
#include <linux/of.h>
#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/string.h>
#include <linux/cpufreq.h>

+#include <asm/cpu.h>
#include <asm/cputype.h>
#include <asm/topology.h>

static DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
+static DEFINE_MUTEX(cpu_scale_mutex);

unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
{
@@ -37,6 +40,65 @@ static void set_capacity_scale(unsigned int cpu, unsigned long capacity)
per_cpu(cpu_scale, cpu) = capacity;
}

+#ifdef CONFIG_PROC_SYSCTL
+static ssize_t cpu_capacity_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct cpu *cpu = container_of(dev, struct cpu, dev);
+
+ return sprintf(buf, "%lu\n",
+ arch_scale_cpu_capacity(NULL, cpu->dev.id));
+}
+
+static ssize_t cpu_capacity_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ struct cpu *cpu = container_of(dev, struct cpu, dev);
+ int this_cpu = cpu->dev.id, i;
+ unsigned long new_capacity;
+ ssize_t ret;
+
+ if (count) {
+ ret = kstrtoul(buf, 0, &new_capacity);
+ if (ret)
+ return ret;
+ if (new_capacity > SCHED_CAPACITY_SCALE)
+ return -EINVAL;
+
+ mutex_lock(&cpu_scale_mutex);
+ for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
+ set_capacity_scale(i, new_capacity);
+ mutex_unlock(&cpu_scale_mutex);
+ }
+
+ return count;
+}
+
+static DEVICE_ATTR_RW(cpu_capacity);
+
+static int register_cpu_capacity_sysctl(void)
+{
+ int i;
+ struct device *cpu;
+
+ for_each_possible_cpu(i) {
+ cpu = get_cpu_device(i);
+ if (!cpu) {
+ pr_err("%s: too early to get CPU%d device!\n",
+ __func__, i);
+ continue;
+ }
+ device_create_file(cpu, &dev_attr_cpu_capacity);
+ }
+
+ return 0;
+}
+subsys_initcall(register_cpu_capacity_sysctl);
+#endif
+
static u32 capacity_scale;
static u32 *raw_capacity;
static bool cap_parsing_failed;
@@ -87,6 +149,7 @@ static void normalize_cpu_capacity(void)
return;

pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
+ mutex_lock(&cpu_scale_mutex);
for_each_possible_cpu(cpu) {
pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
cpu, raw_capacity[cpu]);
@@ -96,6 +159,7 @@ static void normalize_cpu_capacity(void)
pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
cpu, arch_scale_cpu_capacity(NULL, cpu));
}
+ mutex_unlock(&cpu_scale_mutex);
}

#ifdef CONFIG_CPU_FREQ
--
2.10.0
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