linux/drivers/base/cpu.c
Peter Zijlstra 8e7fbcbc22 sched: Remove stale power aware scheduling remnants and dysfunctional knobs
It's been broken forever (i.e. it's not scheduling in a power
aware fashion), as reported by Suresh and others sending
patches, and nobody cares enough to fix it properly ...
so remove it to make space free for something better.

There's various problems with the code as it stands today, first
and foremost the user interface which is bound to topology
levels and has multiple values per level. This results in a
state explosion which the administrator or distro needs to
master and almost nobody does.

Furthermore large configuration state spaces aren't good, it
means the thing doesn't just work right because it's either
under so many impossibe to meet constraints, or even if
there's an achievable state workloads have to be aware of
it precisely and can never meet it for dynamic workloads.

So pushing this kind of decision to user-space was a bad idea
even with a single knob - it's exponentially worse with knobs
on every node of the topology.

There is a proposal to replace the user interface with a single
3 state knob:

 sched_balance_policy := { performance, power, auto }

where 'auto' would be the preferred default which looks at things
like Battery/AC mode and possible cpufreq state or whatever the hw
exposes to show us power use expectations - but there's been no
progress on it in the past many months.

Aside from that, the actual implementation of the various knobs
is known to be broken. There have been sporadic attempts at
fixing things but these always stop short of reaching a mergable
state.

Therefore this wholesale removal with the hopes of spurring
people who care to come forward once again and work on a
coherent replacement.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1326104915.2442.53.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2012-05-17 13:48:56 +02:00

334 lines
8.2 KiB
C

/*
* CPU subsystem support
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/cpu.h>
#include <linux/topology.h>
#include <linux/device.h>
#include <linux/node.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/percpu.h>
#include "base.h"
struct bus_type cpu_subsys = {
.name = "cpu",
.dev_name = "cpu",
};
EXPORT_SYMBOL_GPL(cpu_subsys);
static DEFINE_PER_CPU(struct device *, cpu_sys_devices);
#ifdef CONFIG_HOTPLUG_CPU
static ssize_t show_online(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct cpu *cpu = container_of(dev, struct cpu, dev);
return sprintf(buf, "%u\n", !!cpu_online(cpu->dev.id));
}
static ssize_t __ref store_online(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
struct cpu *cpu = container_of(dev, struct cpu, dev);
ssize_t ret;
cpu_hotplug_driver_lock();
switch (buf[0]) {
case '0':
ret = cpu_down(cpu->dev.id);
if (!ret)
kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
break;
case '1':
ret = cpu_up(cpu->dev.id);
if (!ret)
kobject_uevent(&dev->kobj, KOBJ_ONLINE);
break;
default:
ret = -EINVAL;
}
cpu_hotplug_driver_unlock();
if (ret >= 0)
ret = count;
return ret;
}
static DEVICE_ATTR(online, 0644, show_online, store_online);
static void __cpuinit register_cpu_control(struct cpu *cpu)
{
device_create_file(&cpu->dev, &dev_attr_online);
}
void unregister_cpu(struct cpu *cpu)
{
int logical_cpu = cpu->dev.id;
unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
device_remove_file(&cpu->dev, &dev_attr_online);
device_unregister(&cpu->dev);
per_cpu(cpu_sys_devices, logical_cpu) = NULL;
return;
}
#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
static ssize_t cpu_probe_store(struct device *dev,
struct device_attribute *attr,
const char *buf,
size_t count)
{
return arch_cpu_probe(buf, count);
}
static ssize_t cpu_release_store(struct device *dev,
struct device_attribute *attr,
const char *buf,
size_t count)
{
return arch_cpu_release(buf, count);
}
static DEVICE_ATTR(probe, S_IWUSR, NULL, cpu_probe_store);
static DEVICE_ATTR(release, S_IWUSR, NULL, cpu_release_store);
#endif /* CONFIG_ARCH_CPU_PROBE_RELEASE */
#else /* ... !CONFIG_HOTPLUG_CPU */
static inline void register_cpu_control(struct cpu *cpu)
{
}
#endif /* CONFIG_HOTPLUG_CPU */
#ifdef CONFIG_KEXEC
#include <linux/kexec.h>
static ssize_t show_crash_notes(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct cpu *cpu = container_of(dev, struct cpu, dev);
ssize_t rc;
unsigned long long addr;
int cpunum;
cpunum = cpu->dev.id;
/*
* Might be reading other cpu's data based on which cpu read thread
* has been scheduled. But cpu data (memory) is allocated once during
* boot up and this data does not change there after. Hence this
* operation should be safe. No locking required.
*/
addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpunum));
rc = sprintf(buf, "%Lx\n", addr);
return rc;
}
static DEVICE_ATTR(crash_notes, 0400, show_crash_notes, NULL);
#endif
/*
* Print cpu online, possible, present, and system maps
*/
struct cpu_attr {
struct device_attribute attr;
const struct cpumask *const * const map;
};
static ssize_t show_cpus_attr(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct cpu_attr *ca = container_of(attr, struct cpu_attr, attr);
int n = cpulist_scnprintf(buf, PAGE_SIZE-2, *(ca->map));
buf[n++] = '\n';
buf[n] = '\0';
return n;
}
#define _CPU_ATTR(name, map) \
{ __ATTR(name, 0444, show_cpus_attr, NULL), map }
/* Keep in sync with cpu_subsys_attrs */
static struct cpu_attr cpu_attrs[] = {
_CPU_ATTR(online, &cpu_online_mask),
_CPU_ATTR(possible, &cpu_possible_mask),
_CPU_ATTR(present, &cpu_present_mask),
};
/*
* Print values for NR_CPUS and offlined cpus
*/
static ssize_t print_cpus_kernel_max(struct device *dev,
struct device_attribute *attr, char *buf)
{
int n = snprintf(buf, PAGE_SIZE-2, "%d\n", NR_CPUS - 1);
return n;
}
static DEVICE_ATTR(kernel_max, 0444, print_cpus_kernel_max, NULL);
/* arch-optional setting to enable display of offline cpus >= nr_cpu_ids */
unsigned int total_cpus;
static ssize_t print_cpus_offline(struct device *dev,
struct device_attribute *attr, char *buf)
{
int n = 0, len = PAGE_SIZE-2;
cpumask_var_t offline;
/* display offline cpus < nr_cpu_ids */
if (!alloc_cpumask_var(&offline, GFP_KERNEL))
return -ENOMEM;
cpumask_andnot(offline, cpu_possible_mask, cpu_online_mask);
n = cpulist_scnprintf(buf, len, offline);
free_cpumask_var(offline);
/* display offline cpus >= nr_cpu_ids */
if (total_cpus && nr_cpu_ids < total_cpus) {
if (n && n < len)
buf[n++] = ',';
if (nr_cpu_ids == total_cpus-1)
n += snprintf(&buf[n], len - n, "%d", nr_cpu_ids);
else
n += snprintf(&buf[n], len - n, "%d-%d",
nr_cpu_ids, total_cpus-1);
}
n += snprintf(&buf[n], len - n, "\n");
return n;
}
static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
static void cpu_device_release(struct device *dev)
{
/*
* This is an empty function to prevent the driver core from spitting a
* warning at us. Yes, I know this is directly opposite of what the
* documentation for the driver core and kobjects say, and the author
* of this code has already been publically ridiculed for doing
* something as foolish as this. However, at this point in time, it is
* the only way to handle the issue of statically allocated cpu
* devices. The different architectures will have their cpu device
* code reworked to properly handle this in the near future, so this
* function will then be changed to correctly free up the memory held
* by the cpu device.
*
* Never copy this way of doing things, or you too will be made fun of
* on the linux-kerenl list, you have been warned.
*/
}
/*
* register_cpu - Setup a sysfs device for a CPU.
* @cpu - cpu->hotpluggable field set to 1 will generate a control file in
* sysfs for this CPU.
* @num - CPU number to use when creating the device.
*
* Initialize and register the CPU device.
*/
int __cpuinit register_cpu(struct cpu *cpu, int num)
{
int error;
cpu->node_id = cpu_to_node(num);
memset(&cpu->dev, 0x00, sizeof(struct device));
cpu->dev.id = num;
cpu->dev.bus = &cpu_subsys;
cpu->dev.release = cpu_device_release;
#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
cpu->dev.bus->uevent = arch_cpu_uevent;
#endif
error = device_register(&cpu->dev);
if (!error && cpu->hotpluggable)
register_cpu_control(cpu);
if (!error)
per_cpu(cpu_sys_devices, num) = &cpu->dev;
if (!error)
register_cpu_under_node(num, cpu_to_node(num));
#ifdef CONFIG_KEXEC
if (!error)
error = device_create_file(&cpu->dev, &dev_attr_crash_notes);
#endif
return error;
}
struct device *get_cpu_device(unsigned cpu)
{
if (cpu < nr_cpu_ids && cpu_possible(cpu))
return per_cpu(cpu_sys_devices, cpu);
else
return NULL;
}
EXPORT_SYMBOL_GPL(get_cpu_device);
#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
static DEVICE_ATTR(modalias, 0444, arch_print_cpu_modalias, NULL);
#endif
static struct attribute *cpu_root_attrs[] = {
#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
&dev_attr_probe.attr,
&dev_attr_release.attr,
#endif
&cpu_attrs[0].attr.attr,
&cpu_attrs[1].attr.attr,
&cpu_attrs[2].attr.attr,
&dev_attr_kernel_max.attr,
&dev_attr_offline.attr,
#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
&dev_attr_modalias.attr,
#endif
NULL
};
static struct attribute_group cpu_root_attr_group = {
.attrs = cpu_root_attrs,
};
static const struct attribute_group *cpu_root_attr_groups[] = {
&cpu_root_attr_group,
NULL,
};
bool cpu_is_hotpluggable(unsigned cpu)
{
struct device *dev = get_cpu_device(cpu);
return dev && container_of(dev, struct cpu, dev)->hotpluggable;
}
EXPORT_SYMBOL_GPL(cpu_is_hotpluggable);
#ifdef CONFIG_GENERIC_CPU_DEVICES
static DEFINE_PER_CPU(struct cpu, cpu_devices);
#endif
static void __init cpu_dev_register_generic(void)
{
#ifdef CONFIG_GENERIC_CPU_DEVICES
int i;
for_each_possible_cpu(i) {
if (register_cpu(&per_cpu(cpu_devices, i), i))
panic("Failed to register CPU device");
}
#endif
}
void __init cpu_dev_init(void)
{
if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups))
panic("Failed to register CPU subsystem");
cpu_dev_register_generic();
}