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SubjectRe: [PATCH v7 REPOST 8/9] arm: add sysfs cpu_capacity attribute
Hi,

apologies for the delay in replying, but I'm attending Linux Plumbers
this week.

On 30/10/16 20:45, Russell King - ARM Linux wrote:
> On Mon, Oct 17, 2016 at 04:46:49PM +0100, Juri Lelli wrote:
> > +#ifdef CONFIG_PROC_SYSCTL
> > +#include <asm/cpu.h>
> > +#include <linux/string.h>
>
> Include files at the top of the file please. No need to ifdef them.
> They're sorted alphabetically, so new additions should be alphabetical.
> (That's a general rule - if something is already alphabetical, do not
> make it non-alphabetical.)
>
> > +static ssize_t show_cpu_capacity(struct device *dev,
> > + struct device_attribute *attr,
> > + char *buf)
> > +{
> > + struct cpu *cpu = container_of(dev, struct cpu, dev);
> > + ssize_t rc;
> > + int cpunum = cpu->dev.id;
> > + unsigned long capacity = arch_scale_cpu_capacity(NULL, cpunum);
> > +
> > + rc = sprintf(buf, "%lu\n", capacity);
> > +
> > + return rc;
>
> Way too many lines for such a simple function. This can be simplified
> to just:
>
> struct cpu *cpu = container_of(dev, struct cpu, dev);
>
> return sprintf(buf, "%lu\n", arch_scale_cpu_capacity(NULL, cpu->dev.id);
>
> If you don't like the last line ending on column 79, then feel free to
> break it across two lines after the format string.
>
> > +}
> > +
> > +static ssize_t store_cpu_capacity(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) {
> > + char *p = (char *) buf;
> > +
> > + ret = kstrtoul(p, 0, &new_capacity);
>
> Unnecessary cast - kstrtoul takes a const char pointer, and in any case
> it's really bad form to cast away the "const-ness" of any pointer. So,
> just:
>
> if (count) {
> ret = kstrtoul(buf, 0, &new_capacity);
>
> should work just fine.
>
> > + 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(cpu_capacity,
> > + 0644,
> > + show_cpu_capacity,
> > + store_cpu_capacity);
>
> There's a move to use the named DEVICE_ATTR_RW() for this kind of thing,
> it'll want the functions named xxx_show() and xxx_store(). I see
> there's some recent patches to do this conversion across the kernel, so
> this should probably be done before submission.
>
> > +
> > +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;
> > +}
> > +late_initcall(register_cpu_capacity_sysctl);
>
> Hmm, this is really weird. topology_init() in arch/arm/kernel/setup.c
> is where these devices get created, and they're created at
> subsys_initcall() time. By that point, the list of possible CPUs has
> to be static, it's not going to change. I don't see why this has to be
> done at late_initcall() - and since topology.c will be linked after
> setup.c, I don't see why it shouldn't be at subsys_initcall() level to
> follow on after topology_init().
>

I should have addressed your comments with the updated version below. If
it looks good to you I'll superseed the old version with this new one.

Best,

- Juri

--->8---
From 14c0f21d403ad47843896eecc042334d4e0ed8dd Mon Sep 17 00:00:00 2001
From: Juri Lelli <juri.lelli@arm.com>
Date: Thu, 15 Oct 2015 13:53:37 +0100
Subject: [PATCH v7.1 8/9] arm: 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: Russell King <linux@arm.linux.org.uk>
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/arm/kernel/topology.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 64 insertions(+)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index aa63287d9a10..ebf47d91b804 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -22,7 +22,9 @@
#include <linux/of.h>
#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/string.h>

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

@@ -42,6 +44,7 @@
* updated during this sequence.
*/
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)
{
@@ -53,6 +56,65 @@ 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
+
#ifdef CONFIG_OF
struct cpu_efficiency {
const char *compatible;
@@ -132,6 +194,7 @@ 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) {
capacity = (raw_capacity[cpu] << SCHED_CAPACITY_SHIFT)
/ capacity_scale;
@@ -139,6 +202,7 @@ 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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