cpufreq: Add mechanism for registering utilization update callbacks

Introduce a mechanism by which parts of the cpufreq subsystem
("setpolicy" drivers or the core) can register callbacks to be
executed from cpufreq_update_util() which is invoked by the
scheduler's update_load_avg() on CPU utilization changes.

This allows the "setpolicy" drivers to dispense with their timers
and do all of the computations they need and frequency/voltage
adjustments in the update_load_avg() code path, among other things.

The update_load_avg() changes were suggested by Peter Zijlstra.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Rafael J. Wysocki 2016-02-15 20:20:42 +01:00
parent de1df26b7c
commit 34e2c555f3
6 changed files with 113 additions and 1 deletions

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@ -102,6 +102,51 @@ static LIST_HEAD(cpufreq_governor_list);
static struct cpufreq_driver *cpufreq_driver;
static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
static DEFINE_RWLOCK(cpufreq_driver_lock);
static DEFINE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
/**
* cpufreq_set_update_util_data - Populate the CPU's update_util_data pointer.
* @cpu: The CPU to set the pointer for.
* @data: New pointer value.
*
* Set and publish the update_util_data pointer for the given CPU. That pointer
* points to a struct update_util_data object containing a callback function
* to call from cpufreq_update_util(). That function will be called from an RCU
* read-side critical section, so it must not sleep.
*
* Callers must use RCU callbacks to free any memory that might be accessed
* via the old update_util_data pointer or invoke synchronize_rcu() right after
* this function to avoid use-after-free.
*/
void cpufreq_set_update_util_data(int cpu, struct update_util_data *data)
{
rcu_assign_pointer(per_cpu(cpufreq_update_util_data, cpu), data);
}
EXPORT_SYMBOL_GPL(cpufreq_set_update_util_data);
/**
* cpufreq_update_util - Take a note about CPU utilization changes.
* @time: Current time.
* @util: Current utilization.
* @max: Utilization ceiling.
*
* This function is called by the scheduler on every invocation of
* update_load_avg() on the CPU whose utilization is being updated.
*/
void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
{
struct update_util_data *data;
rcu_read_lock();
data = rcu_dereference(*this_cpu_ptr(&cpufreq_update_util_data));
if (data && data->func)
data->func(data, time, util, max);
rcu_read_unlock();
}
DEFINE_MUTEX(cpufreq_governor_lock);
/* Flag to suspend/resume CPUFreq governors */

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@ -151,6 +151,36 @@ static inline bool policy_is_shared(struct cpufreq_policy *policy)
extern struct kobject *cpufreq_global_kobject;
#ifdef CONFIG_CPU_FREQ
void cpufreq_update_util(u64 time, unsigned long util, unsigned long max);
/**
* cpufreq_trigger_update - Trigger CPU performance state evaluation if needed.
* @time: Current time.
*
* The way cpufreq is currently arranged requires it to evaluate the CPU
* performance state (frequency/voltage) on a regular basis to prevent it from
* being stuck in a completely inadequate performance level for too long.
* That is not guaranteed to happen if the updates are only triggered from CFS,
* though, because they may not be coming in if RT or deadline tasks are active
* all the time (or there are RT and DL tasks only).
*
* As a workaround for that issue, this function is called by the RT and DL
* sched classes to trigger extra cpufreq updates to prevent it from stalling,
* but that really is a band-aid. Going forward it should be replaced with
* solutions targeted more specifically at RT and DL tasks.
*/
static inline void cpufreq_trigger_update(u64 time)
{
cpufreq_update_util(time, ULONG_MAX, 0);
}
struct update_util_data {
void (*func)(struct update_util_data *data,
u64 time, unsigned long util, unsigned long max);
};
void cpufreq_set_update_util_data(int cpu, struct update_util_data *data);
unsigned int cpufreq_get(unsigned int cpu);
unsigned int cpufreq_quick_get(unsigned int cpu);
unsigned int cpufreq_quick_get_max(unsigned int cpu);
@ -162,6 +192,10 @@ int cpufreq_update_policy(unsigned int cpu);
bool have_governor_per_policy(void);
struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
#else
static inline void cpufreq_update_util(u64 time, unsigned long util,
unsigned long max) {}
static inline void cpufreq_trigger_update(u64 time) {}
static inline unsigned int cpufreq_get(unsigned int cpu)
{
return 0;

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@ -726,6 +726,10 @@ static void update_curr_dl(struct rq *rq)
if (!dl_task(curr) || !on_dl_rq(dl_se))
return;
/* Kick cpufreq (see the comment in linux/cpufreq.h). */
if (cpu_of(rq) == smp_processor_id())
cpufreq_trigger_update(rq_clock(rq));
/*
* Consumed budget is computed considering the time as
* observed by schedulable tasks (excluding time spent

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@ -2824,7 +2824,8 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
{
struct cfs_rq *cfs_rq = cfs_rq_of(se);
u64 now = cfs_rq_clock_task(cfs_rq);
int cpu = cpu_of(rq_of(cfs_rq));
struct rq *rq = rq_of(cfs_rq);
int cpu = cpu_of(rq);
/*
* Track task load average for carrying it to new CPU after migrated, and
@ -2836,6 +2837,29 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
if (update_cfs_rq_load_avg(now, cfs_rq) && update_tg)
update_tg_load_avg(cfs_rq, 0);
if (cpu == smp_processor_id() && &rq->cfs == cfs_rq) {
unsigned long max = rq->cpu_capacity_orig;
/*
* There are a few boundary cases this might miss but it should
* get called often enough that that should (hopefully) not be
* a real problem -- added to that it only calls on the local
* CPU, so if we enqueue remotely we'll miss an update, but
* the next tick/schedule should update.
*
* It will not get called when we go idle, because the idle
* thread is a different class (!fair), nor will the utilization
* number include things like RT tasks.
*
* As is, the util number is not freq-invariant (we'd have to
* implement arch_scale_freq_capacity() for that).
*
* See cpu_util().
*/
cpufreq_update_util(rq_clock(rq),
min(cfs_rq->avg.util_avg, max), max);
}
}
static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)

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@ -945,6 +945,10 @@ static void update_curr_rt(struct rq *rq)
if (curr->sched_class != &rt_sched_class)
return;
/* Kick cpufreq (see the comment in linux/cpufreq.h). */
if (cpu_of(rq) == smp_processor_id())
cpufreq_trigger_update(rq_clock(rq));
delta_exec = rq_clock_task(rq) - curr->se.exec_start;
if (unlikely((s64)delta_exec <= 0))
return;

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@ -9,6 +9,7 @@
#include <linux/irq_work.h>
#include <linux/tick.h>
#include <linux/slab.h>
#include <linux/cpufreq.h>
#include "cpupri.h"
#include "cpudeadline.h"