Re: [PATCH v2 1/10] cpufreq: Reduce cpufreq_update_util() overhead a bit

Rafael J. Wysocki
2016-03-09T21:35:02Z

On Wednesday, March 09, 2016 04:29:34 PM Peter Zijlstra wrote:
> On Wed, Mar 09, 2016 at 03:17:48PM +0100, Rafael J. Wysocki wrote:
> > > That said, how about the below? It avoids a function call.
> >
> > That is fine by me.
> >
> > What about taking it a bit further, though, and moving the definition
> > of cpufreq_update_util_data to somewhere under kernel/sched/ (like
> > kernel/sched/cpufreq.c maybe)?
> >
> > Then, the whole static inline void cpufreq_update_util() definition
> > can go into kernel/sched/sched.h (it doesn't have to be visible
> > anywhere beyond kernel/sched/) and the only thing that needs to be
> > exported to cpufreq will be a helper (or two), to set/clear the
> > cpufreq_update_util_data pointers.
> >
> > I'll try to cut a patch doing that later today for illustration.
>
> Right, that's a blend with your second patch. Sure.

OK, patch below.

---
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH] cpufreq: Move scheduler-related code to the sched directory

Create cpufreq.c under kernel/sched/ and move the cpufreq code
related to the scheduler to that file and to sched.h.

Redefine cpufreq_update_util() as a static inline function to avoid
function calls at its call sites in the scheduler code (as suggested
by Peter Zijlstra).

Also move the definition of struct update_util_data and declaration
of cpufreq_set_update_util_data() from include/linux/cpufreq.h to
include/linux/sched.h.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpufreq/cpufreq.c | 53 -------------------------------------
drivers/cpufreq/cpufreq_governor.c | 1
include/linux/cpufreq.h | 34 -----------------------
include/linux/sched.h | 9 ++++++
kernel/sched/Makefile | 1
kernel/sched/cpufreq.c | 37 +++++++++++++++++++++++++
kernel/sched/sched.h | 49 +++++++++++++++++++++++++++++++++-
7 files changed, 96 insertions(+), 88 deletions(-)

Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -65,59 +65,6 @@ static struct cpufreq_driver *cpufreq_dr
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-sched callbacks to free any memory that might be
- * accessed via the old update_util_data pointer or invoke synchronize_sched()
- * right after this function to avoid use-after-free.
- */
-void cpufreq_set_update_util_data(int cpu, struct update_util_data *data)
-{
- if (WARN_ON(data && !data->func))
- return;
-
- 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.
- *
- * It can only be called from RCU-sched read-side critical sections.
- */
-void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
-{
- struct update_util_data *data;
-
-#ifdef CONFIG_LOCKDEP
- WARN_ON(debug_locks && !rcu_read_lock_sched_held());
-#endif
-
- data = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_update_util_data));
- /*
- * If this isn't inside of an RCU-sched read-side critical section, data
- * may become NULL after the check below.
- */
- if (data)
- data->func(data, time, util, max);
-}
-
/* Flag to suspend/resume CPUFreq governors */
static bool cpufreq_suspended;

Index: linux-pm/include/linux/cpufreq.h
===================================================================
--- linux-pm.orig/include/linux/cpufreq.h
+++ linux-pm/include/linux/cpufreq.h
@@ -146,36 +146,6 @@ 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 (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);
@@ -187,10 +157,6 @@ 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/cpufreq.c
===================================================================
--- /dev/null
+++ linux-pm/kernel/sched/cpufreq.c
@@ -0,0 +1,37 @@
+/*
+ * Scheduler code and data structures related to cpufreq.
+ *
+ * Copyright (C) 2016, Intel Corporation
+ * Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include "sched.h"
+
+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-sched callbacks to free any memory that might be
+ * accessed via the old update_util_data pointer or invoke synchronize_sched()
+ * right after this function to avoid use-after-free.
+ */
+void cpufreq_set_update_util_data(int cpu, struct update_util_data *data)
+{
+ if (WARN_ON(data && !data->func))
+ return;
+
+ rcu_assign_pointer(per_cpu(cpufreq_update_util_data, cpu), data);
+}
+EXPORT_SYMBOL_GPL(cpufreq_set_update_util_data);
Index: linux-pm/kernel/sched/sched.h
===================================================================
--- linux-pm.orig/kernel/sched/sched.h
+++ linux-pm/kernel/sched/sched.h
@@ -9,7 +9,6 @@
#include <linux/irq_work.h>
#include <linux/tick.h>
#include <linux/slab.h>
-#include <linux/cpufreq.h>

#include "cpupri.h"
#include "cpudeadline.h"
@@ -1739,3 +1738,51 @@ static inline u64 irq_time_read(int cpu)
}
#endif /* CONFIG_64BIT */
#endif /* CONFIG_IRQ_TIME_ACCOUNTING */
+
+#ifdef CONFIG_CPU_FREQ
+DECLARE_PER_CPU(struct update_util_data *, cpufreq_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.
+ *
+ * It can only be called from RCU-sched read-side critical sections.
+ */
+static inline void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
+{
+ struct update_util_data *data;
+
+ data = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_update_util_data));
+ if (data)
+ data->func(data, time, util, 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);
+}
+#else
+static inline void cpufreq_update_util(u64 time, unsigned long util, unsigned long max) {}
+static inline void cpufreq_trigger_update(u64 time) {}
+#endif /* CONFIG_CPU_FREQ */
Index: linux-pm/include/linux/sched.h
===================================================================
--- linux-pm.orig/include/linux/sched.h
+++ linux-pm/include/linux/sched.h
@@ -3207,4 +3207,13 @@ static inline unsigned long rlimit_max(u
return task_rlimit_max(current, limit);
}

+#ifdef CONFIG_CPU_FREQ
+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);
+#endif /* CONFIG_CPU_FREQ */
+
#endif
Index: linux-pm/drivers/cpufreq/cpufreq_governor.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq_governor.c
+++ linux-pm/drivers/cpufreq/cpufreq_governor.c
@@ -18,6 +18,7 @@

#include <linux/export.h>
#include <linux/kernel_stat.h>
+#include <linux/sched.h>
#include <linux/slab.h>

#include "cpufreq_governor.h"
Index: linux-pm/kernel/sched/Makefile
===================================================================
--- linux-pm.orig/kernel/sched/Makefile
+++ linux-pm/kernel/sched/Makefile
@@ -19,3 +19,4 @@ obj-$(CONFIG_SCHED_AUTOGROUP) += auto_gr
obj-$(CONFIG_SCHEDSTATS) += stats.o
obj-$(CONFIG_SCHED_DEBUG) += debug.o
obj-$(CONFIG_CGROUP_CPUACCT) += cpuacct.o
+obj-$(CONFIG_CPU_FREQ) += cpufreq.o