Re: [PATCH 2/3] sched: idle: Add sched balance option
From: Daniel Lezcano
Date: Thu Apr 24 2014 - 09:29:49 EST
On 04/24/2014 03:13 PM, Amit Kucheria wrote:
On Thu, Apr 24, 2014 at 5:54 PM, Daniel Lezcano
<daniel.lezcano@xxxxxxxxxx <mailto:daniel.lezcano@xxxxxxxxxx>> wrote:
This patch adds a sysctl schedule balance option to choose against:
* auto (0)
* performance (1)
* power (2)
It relies on the recently added notifier to monitor the power supply
changes.
If the scheduler balance option is set to 'auto', then when the
system switches
to battery, the balance option change to 'power' and when it goes
back to AC, it
switches to 'performance'.
The default value is 'auto'.
If the kernel is compiled without the CONFIG_POWER_SUPPLY option,
then any call
to the 'auto' option will fail and the scheduler will use the
'performance'
option as default.
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx
<mailto:daniel.lezcano@xxxxxxxxxx>>
---
include/linux/sched/sysctl.h | 14 +++++++
kernel/sched/fair.c | 92
+++++++++++++++++++++++++++++++++++++++++-
kernel/sysctl.c | 11 +++++
3 files changed, 115 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index 8045a55..f8507bf 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -44,6 +44,20 @@ enum sched_tunable_scaling {
};
extern enum sched_tunable_scaling sysctl_sched_tunable_scaling;
+#ifdef CONFIG_SMP
+enum sched_balance_option {
What do you think of s/option/bias/g ?
It is essentially biasing the scheduler towards performance or power
Yes, could be more adequate.
+ SCHED_BALANCE_OPTION_PERFORMANCE,
+ SCHED_BALANCE_OPTION_POWER,
+ SCHED_BALANCE_OPTION_AUTO,
+ SCHED_BALANCE_OPTION_END,
+};
+extern enum sched_balance_option sysctl_sched_balance_option;
+
+int sched_proc_balance_option_handler(struct ctl_table *table, int
write,
+ void __user *buffer, size_t *length,
+ loff_t *ppos);
+#endif
+
extern unsigned int sysctl_numa_balancing_scan_delay;
extern unsigned int sysctl_numa_balancing_scan_period_min;
extern unsigned int sysctl_numa_balancing_scan_period_max;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7570dd9..7b8e93d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -29,7 +29,7 @@
#include <linux/mempolicy.h>
#include <linux/migrate.h>
#include <linux/task_work.h>
-
+#include <linux/power_supply.h>
#include <trace/events/sched.h>
#include "sched.h"
@@ -61,6 +61,24 @@ unsigned int normalized_sysctl_sched_latency =
6000000ULL;
enum sched_tunable_scaling sysctl_sched_tunable_scaling
= SCHED_TUNABLESCALING_LOG;
+#ifdef CONFIG_SMP
+/*
+ * Scheduler balancing policy:
+ *
+ * Options are:
+ * SCHED_BALANCE_OPTION_PERFORMANCE - full performance
+ * SCHED_BALANCE_OPTION_POWER - power saving aggressive
+ * SCHED_BALANCE_OPTION_AUTO - switches to 'performance' when plugged
+ * on or 'power' on battery
+ */
+enum sched_balance_option sysctl_sched_balance_option
+ = SCHED_BALANCE_OPTION_AUTO;
+
+static int sched_current_balance_option
+ = SCHED_BALANCE_OPTION_PERFORMANCE;
+
+#endif
+
/*
* Minimal preemption granularity for CPU-bound tasks:
* (default: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
@@ -555,6 +573,76 @@ static struct sched_entity
*__pick_next_entity(struct sched_entity *se)
return rb_entry(next, struct sched_entity, run_node);
}
+#ifdef CONFIG_SMP
+static int sched_balance_option_update(void)
+{
+ int ret;
+
+ /*
+ * Copy the current balance option
+ */
+ if (sysctl_sched_balance_option != SCHED_BALANCE_OPTION_AUTO) {
+ sched_current_balance_option =
sysctl_sched_balance_option;
+ return 0;
+ }
+
+ /*
+ * This call may fail if the kernel is not compiled with
+ * the POWER_SUPPLY option.
+ */
+ ret = power_supply_is_system_supplied();
+ if (ret < 0) {
+ sysctl_sched_balance_option =
sched_current_balance_option;
+ return ret;
+ }
+
+ /*
+ * When in 'auto' mode, switch to 'performance if the system
+ * is plugged on the wall, to 'power' if we are on battery
+ */
+ sched_current_balance_option = ret ?
+ SCHED_BALANCE_OPTION_PERFORMANCE :
+ SCHED_BALANCE_OPTION_POWER;
+
+ return 0;
+}
+
I understand that this is only meant to kick off discussions and other
criteria besides power being plugged in to bias the scheduler
performance could be added later. But does it make sense to hardcode the
power supply assumption into the scheduler?
Can't we instead make sched_balance_option_update() a function pointer
(with a default implementation that you've provided) that provide
platforms the ability to override that with their own implementation?
I agree if that really hurts, it could be placed somewhere else, for
example in a new file:
kernel/sched/energy.c
But concerning the callback, I don't see the point to create a specific
platform ops for that as the current code is generic. Do you have any
use case in mind ?
Thanks for the review
-- Daniel
+int sched_proc_balance_option_handler(struct ctl_table *table, int
write,
+ void __user *buffer, size_t *length,
+ loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
+ if (ret)
+ return ret;
+
+ return sched_balance_option_update();
+}
+
+static int sched_power_supply_notifier(struct notifier_block *b,
+ unsigned long l, void *v)
+{
+ sched_balance_option_update();
+ return NOTIFY_OK;
+}
+
+static struct notifier_block power_supply_notifier_nb = {
+ .notifier_call = sched_power_supply_notifier,
+};
+
+static int sched_balance_option_init(void)
+{
+ int ret;
+
+ ret = sched_balance_option_update();
+ if (ret)
+ return ret;
+
+ return power_supply_reg_notifier(&power_supply_notifier_nb);
+}
+#endif
+
#ifdef CONFIG_SCHED_DEBUG
struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
@@ -7695,7 +7783,7 @@ __init void init_sched_fair_class(void)
{
#ifdef CONFIG_SMP
open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);
-
+ sched_balance_option_init();
#ifdef CONFIG_NO_HZ_COMMON
nohz.next_balance = jiffies;
zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 74f5b58..e4ecc7d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -282,6 +282,17 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+#ifdef CONFIG_SMP
+ {
+ .procname = "sched_balance_option",
+ .data = &sysctl_sched_balance_option,
+ .maxlen = sizeof(enum sched_balance_option),
+ .mode = 0644,
+ .proc_handler = sched_proc_balance_option_handler,
+ .extra1 = &zero, /* SCHED_BALANCE_OPTION_AUTO */
+ .extra2 = &two, /*
SCHED_BALANCE_OPTION_POWER */
+ },
+#endif
#ifdef CONFIG_SCHED_DEBUG
{
.procname = "sched_min_granularity_ns",
--
1.7.9.5
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