From: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
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.wyso...@intel.com>
Acked-by: Viresh Kumar <viresh.ku...@linaro.org>
---
Changes from v7
- cpufreq_trigger_update() has a kerneldoc describing it as a band-aid to
be replaced in the future and the comments next to its call sites ask
the reader to see that comment.
No functional changes.
Changes from v6:
- Steve suggested to use rq_clock() instead of rq_clock_task() as the time
argument for cpufreq_update_util() as that seems to be more suitable for
this purpose.
---
drivers/cpufreq/cpufreq.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/cpufreq.h | 34 ++++++++++++++++++++++++++++++++++
kernel/sched/deadline.c | 3 +++
kernel/sched/fair.c | 26 +++++++++++++++++++++++++-
kernel/sched/rt.c | 3 +++
kernel/sched/sched.h | 1 +
6 files changed, 111 insertions(+), 1 deletion(-)
Index: linux-pm/include/linux/cpufreq.h
===================================================================
--- linux-pm.orig/include/linux/cpufreq.h
+++ linux-pm/include/linux/cpufreq.h
@@ -151,6 +151,36 @@ static inline bool policy_is_shared(stru
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.
+ *
+ * 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 c
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;
Index: linux-pm/kernel/sched/sched.h
===================================================================
--- linux-pm.orig/kernel/sched/sched.h
+++ linux-pm/kernel/sched/sched.h
@@ -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"
Index: linux-pm/kernel/sched/fair.c
===================================================================
--- linux-pm.orig/kernel/sched/fair.c
+++ linux-pm/kernel/sched/fair.c
@@ -2824,7 +2824,8 @@ static inline void update_load_avg(struc
{
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(struc
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)
Index: linux-pm/kernel/sched/deadline.c
===================================================================
--- linux-pm.orig/kernel/sched/deadline.c
+++ linux-pm/kernel/sched/deadline.c
@@ -726,6 +726,9 @@ 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). */
+ cpufreq_trigger_update(rq_clock(rq));
+
/*
* Consumed budget is computed considering the time as
* observed by schedulable tasks (excluding time spent
Index: linux-pm/kernel/sched/rt.c
===================================================================
--- linux-pm.orig/kernel/sched/rt.c
+++ linux-pm/kernel/sched/rt.c
@@ -949,6 +949,9 @@ static void update_curr_rt(struct rq *rq
if (unlikely((s64)delta_exec <= 0))
return;
+ /* Kick cpufreq (see the comment in linux/cpufreq.h). */
+ cpufreq_trigger_update(rq_clock(rq));
+
schedstat_set(curr->se.statistics.exec_max,
max(curr->se.statistics.exec_max, delta_exec));
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -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 */
