[RFC PATCH v1 1/2] sched: unified sched_powersavings sysfs tunable

From: Vaidyanathan Srinivasan
Date: Mon Jan 16 2012 - 11:23:04 EST

Combine the sched_mc_powersavings and sched_smt_powersavings sysfs
tunables into a single sysfs tunable:

/sys/devices/system/cpu/sched_powersavings={0,1,2}

0 - Power savings disabled (performance mode)
1 - Default kernel settings. Automatic powersave
vs performance tradeoff by the kernel
2 - Maximum power savings

The kernel will default to '1' which is equivalent to
sched_mc_powersavings=1 or consolidate at package level.

Max power saving setting '2' would consolidate to sibling threads and
also do aggressive active balancing.

Signed-off-by: Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx>
---
arch/x86/Kconfig | 20 ++++--------
arch/x86/kernel/smpboot.c | 2 +
block/blk.h | 11 ++++---
drivers/base/cpu.c | 2 +
include/linux/sched.h | 29 +++++++++--------
include/linux/topology.h | 9 +----
kernel/sched/core.c | 75 +++++++++++----------------------------------
kernel/sched/fair.c | 23 +++++++-------
8 files changed, 62 insertions(+), 109 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6c14ecd..ee615af 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -788,23 +788,15 @@ config NR_CPUS
This is purely to save memory - each supported CPU adds
approximately eight kilobytes to the kernel image.

-config SCHED_SMT
- bool "SMT (Hyperthreading) scheduler support"
- depends on X86_HT
- ---help---
- SMT scheduler support improves the CPU scheduler's decision making
- when dealing with Intel Pentium 4 chips with HyperThreading at a
- cost of slightly increased overhead in some places. If unsure say
- N here.
-
-config SCHED_MC
+config SCHED_POWERSAVE
def_bool y
- prompt "Multi-core scheduler support"
+ prompt "Power save support in scheduler"
depends on X86_HT
---help---
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
+ Power saving feature in scheduler optimizes task placement
+ in a multi-core or mulit-threaded system whenever possible.
+ Default kernel settings would suit most applications, while
+ sysfs tunables can be used to control this feature at runtime.

config IRQ_TIME_ACCOUNTING
bool "Fine granularity task level IRQ time accounting"
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 66d250c..1d60cdd 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -414,7 +414,7 @@ const struct cpumask *cpu_coregroup_mask(int cpu)
* For perf, we return last level cache shared map.
* And for power savings, we return cpu_core_map
*/
- if ((sched_mc_power_savings || sched_smt_power_savings) &&
+ if ((sched_power_savings) &&
!(cpu_has(c, X86_FEATURE_AMD_DCM)))
return cpu_core_mask(cpu);
else
diff --git a/block/blk.h b/block/blk.h
index 7efd772..1457107 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -167,14 +167,15 @@ static inline int queue_congestion_off_threshold(struct request_queue *q)
static inline int blk_cpu_to_group(int cpu)
{
int group = NR_CPUS;
-#ifdef CONFIG_SCHED_MC
- const struct cpumask *mask = cpu_coregroup_mask(cpu);
- group = cpumask_first(mask);
-#elif defined(CONFIG_SCHED_SMT)
- group = cpumask_first(topology_thread_cpumask(cpu));
+#ifdef CONFIG_SCHED_POWERSAVE
+ if (smt_capable())
+ group = cpumask_first(topology_thread_cpumask(cpu));
+ else
+ group = cpumask_first(cpu_coregroup_mask(cpu));
#else
return cpu;
#endif
+ /* Possible dead code?? */
if (likely(group < NR_CPUS))
return group;
return cpu;
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index db87e78..dbaa35f 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -299,7 +299,7 @@ void __init cpu_dev_init(void)

cpu_dev_register_generic();

-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+#ifdef CONFIG_SCHED_POWERSAVE
sched_create_sysfs_power_savings_entries(cpu_subsys.dev_root);
#endif
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4032ec1..5c33bbc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -850,33 +850,34 @@ enum cpu_idle_type {
#define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling domain */
#define SD_OVERLAP 0x2000 /* sched_domains of this level overlap */

-enum powersavings_balance_level {
- POWERSAVINGS_BALANCE_NONE = 0, /* No power saving load balance */
- POWERSAVINGS_BALANCE_BASIC, /* Fill one thread/core/package
- * first for long running threads
- */
- POWERSAVINGS_BALANCE_WAKEUP, /* Also bias task wakeups to semi-idle
- * cpu package for power savings
- */
- MAX_POWERSAVINGS_BALANCE_LEVELS
+enum powersavings_level {
+ POWERSAVINGS_DISABLED = 0, /* Max performance */
+ POWERSAVINGS_DEFAULT, /* Kernel default policy, automatic powersave */
+ /* vs performance tradeoff */
+ POWERSAVINGS_MAX /* Favour power savings over peformance */
};

-extern int sched_mc_power_savings, sched_smt_power_savings;
+extern int sched_power_savings;

static inline int sd_balance_for_mc_power(void)
{
- if (sched_smt_power_savings)
+ switch (sched_power_savings) {
+ case POWERSAVINGS_MAX:
return SD_POWERSAVINGS_BALANCE;

- if (!sched_mc_power_savings)
+ case POWERSAVINGS_DISABLED:
return SD_PREFER_SIBLING;

+ default:
+ break;
+ }
+
return 0;
}

static inline int sd_balance_for_package_power(void)
{
- if (sched_mc_power_savings | sched_smt_power_savings)
+ if (sched_power_savings != POWERSAVINGS_DISABLED)
return SD_POWERSAVINGS_BALANCE;

return SD_PREFER_SIBLING;
@@ -892,7 +893,7 @@ extern int __weak arch_sd_sibiling_asym_packing(void);

static inline int sd_power_saving_flags(void)
{
- if (sched_mc_power_savings | sched_smt_power_savings)
+ if (sched_power_savings != POWERSAVINGS_DISABLED)
return SD_BALANCE_NEWIDLE;

return 0;
diff --git a/include/linux/topology.h b/include/linux/topology.h
index e26db03..61f3659 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -79,10 +79,7 @@ int arch_update_cpu_topology(void);
* (Only non-zero and non-null fields need be specified.)
*/

-#ifdef CONFIG_SCHED_SMT
-/* MCD - Do we really need this? It is always on if CONFIG_SCHED_SMT is,
- * so can't we drop this in favor of CONFIG_SCHED_SMT?
- */
+#ifdef CONFIG_SCHED_POWERSAVE
#define ARCH_HAS_SCHED_WAKE_IDLE
/* Common values for SMT siblings */
#ifndef SD_SIBLING_INIT
@@ -110,9 +107,7 @@ int arch_update_cpu_topology(void);
.smt_gain = 1178, /* 15% */ \
}
#endif
-#endif /* CONFIG_SCHED_SMT */

-#ifdef CONFIG_SCHED_MC
/* Common values for MC siblings. for now mostly derived from SD_CPU_INIT */
#ifndef SD_MC_INIT
#define SD_MC_INIT (struct sched_domain) { \
@@ -142,7 +137,7 @@ int arch_update_cpu_topology(void);
.balance_interval = 1, \
}
#endif
-#endif /* CONFIG_SCHED_MC */
+#endif /* CONFIG_SCHED_POWERSAVE */

/* Common values for CPUs */
#ifndef SD_CPU_INIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df00cb0..f303db8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5924,7 +5924,7 @@ static const struct cpumask *cpu_cpu_mask(int cpu)
return cpumask_of_node(cpu_to_node(cpu));
}

-int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
+int sched_power_savings = POWERSAVINGS_DEFAULT;

struct sd_data {
struct sched_domain **__percpu sd;
@@ -6150,10 +6150,8 @@ SD_INIT_FUNC(CPU)
SD_INIT_FUNC(ALLNODES)
SD_INIT_FUNC(NODE)
#endif
-#ifdef CONFIG_SCHED_SMT
+#ifdef CONFIG_SCHED_POWERSAVE
SD_INIT_FUNC(SIBLING)
-#endif
-#ifdef CONFIG_SCHED_MC
SD_INIT_FUNC(MC)
#endif
#ifdef CONFIG_SCHED_BOOK
@@ -6250,7 +6248,7 @@ static void claim_allocations(int cpu, struct sched_domain *sd)
*per_cpu_ptr(sdd->sgp, cpu) = NULL;
}

-#ifdef CONFIG_SCHED_SMT
+#ifdef CONFIG_SCHED_POWERSAVE
static const struct cpumask *cpu_smt_mask(int cpu)
{
return topology_thread_cpumask(cpu);
@@ -6261,10 +6259,8 @@ static const struct cpumask *cpu_smt_mask(int cpu)
* Topology list, bottom-up.
*/
static struct sched_domain_topology_level default_topology[] = {
-#ifdef CONFIG_SCHED_SMT
+#ifdef CONFIG_SCHED_POWERSAVE
{ sd_init_SIBLING, cpu_smt_mask, },
-#endif
-#ifdef CONFIG_SCHED_MC
{ sd_init_MC, cpu_coregroup_mask, },
#endif
#ifdef CONFIG_SCHED_BOOK
@@ -6635,7 +6631,7 @@ match2:
mutex_unlock(&sched_domains_mutex);
}

-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+#if defined(CONFIG_SCHED_POWERSAVE)
static void reinit_sched_domains(void)
{
get_online_cpus();
@@ -6647,7 +6643,9 @@ static void reinit_sched_domains(void)
put_online_cpus();
}

-static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)
+static ssize_t sched_power_savings_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
{
unsigned int level = 0;

@@ -6656,75 +6654,40 @@ static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)

/*
* level is always be positive so don't check for
- * level < POWERSAVINGS_BALANCE_NONE which is 0
+ * level < POWERSAVINGS_DEFAULT which is 0
* What happens on 0 or 1 byte write,
* need to check for count as well?
*/

- if (level >= MAX_POWERSAVINGS_BALANCE_LEVELS)
+ if (level > POWERSAVINGS_MAX)
return -EINVAL;

- if (smt)
- sched_smt_power_savings = level;
- else
- sched_mc_power_savings = level;
+ sched_power_savings = level;

reinit_sched_domains();

return count;
}

-#ifdef CONFIG_SCHED_MC
-static ssize_t sched_mc_power_savings_show(struct device *dev,
+static ssize_t sched_power_savings_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
- return sprintf(buf, "%u\n", sched_mc_power_savings);
-}
-static ssize_t sched_mc_power_savings_store(struct device *dev,
- struct device_attribute *attr,
- const char *buf, size_t count)
-{
- return sched_power_savings_store(buf, count, 0);
-}
-static DEVICE_ATTR(sched_mc_power_savings, 0644,
- sched_mc_power_savings_show,
- sched_mc_power_savings_store);
-#endif
-
-#ifdef CONFIG_SCHED_SMT
-static ssize_t sched_smt_power_savings_show(struct device *dev,
- struct device_attribute *attr,
- char *buf)
-{
- return sprintf(buf, "%u\n", sched_smt_power_savings);
-}
-static ssize_t sched_smt_power_savings_store(struct device *dev,
- struct device_attribute *attr,
- const char *buf, size_t count)
-{
- return sched_power_savings_store(buf, count, 1);
+ return sprintf(buf, "%u\n", sched_power_savings);
}
-static DEVICE_ATTR(sched_smt_power_savings, 0644,
- sched_smt_power_savings_show,
- sched_smt_power_savings_store);
-#endif
+static DEVICE_ATTR(sched_power_savings, 0644,
+ sched_power_savings_show,
+ sched_power_savings_store);

int __init sched_create_sysfs_power_savings_entries(struct device *dev)
{
int err = 0;

-#ifdef CONFIG_SCHED_SMT
- if (smt_capable())
- err = device_create_file(dev, &dev_attr_sched_smt_power_savings);
-#endif
-#ifdef CONFIG_SCHED_MC
- if (!err && mc_capable())
- err = device_create_file(dev, &dev_attr_sched_mc_power_savings);
-#endif
+ if (mc_capable() || smt_capable())
+ err = device_create_file(dev, &dev_attr_sched_power_savings);
return err;
}
-#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+#endif /* CONFIG_SCHED_POWERSAVE */

/*
* Update cpusets according to cpu_active mask. If cpusets are
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 84adb2d..bae6ec8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3497,7 +3497,7 @@ struct sd_lb_stats {
unsigned int busiest_group_weight;

int group_imb; /* Is there imbalance in this sd */
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+#ifdef CONFIG_SCHED_POWERSAVE
int power_savings_balance; /* Is powersave balance needed for this sd */
struct sched_group *group_min; /* Least loaded group in sd */
struct sched_group *group_leader; /* Group which relieves group_min */
@@ -3549,7 +3549,7 @@ static inline int get_sd_load_idx(struct sched_domain *sd,
}


-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+#ifdef CONFIG_SCHED_POWERSAVE
/**
* init_sd_power_savings_stats - Initialize power savings statistics for
* the given sched_domain, during load balancing.
@@ -3669,7 +3669,7 @@ static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
return 1;

}
-#else /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+#else /* CONFIG_SCHED_POWERSAVE */
static inline void init_sd_power_savings_stats(struct sched_domain *sd,
struct sd_lb_stats *sds, enum cpu_idle_type idle)
{
@@ -3687,7 +3687,7 @@ static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
{
return 0;
}
-#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+#endif /* CONFIG_SCHED_POWERSAVE */


unsigned long default_scale_freq_power(struct sched_domain *sd, int cpu)
@@ -4422,9 +4422,10 @@ static int need_active_balance(struct sched_domain *sd, int idle,
*
* The package power saving logic comes from
* find_busiest_group(). If there are no imbalance, then
- * f_b_g() will return NULL. However when sched_mc={1,2} then
- * f_b_g() will select a group from which a running task may be
- * pulled to this cpu in order to make the other package idle.
+ * f_b_g() will return NULL. However when
+ * sched_powersavings={1,2} then f_b_g() will select a group
+ * from which a running task may be pulled to this cpu
+ * in order to make the other package idle.
* If there is no opportunity to make a package idle and if
* there are no imbalance, then f_b_g() will return NULL and no
* action will be taken in load_balance_newidle().
@@ -4434,7 +4435,7 @@ static int need_active_balance(struct sched_domain *sd, int idle,
* move_tasks() will succeed. ld_moved will be true and this
* active balance code will not be triggered.
*/
- if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
+ if (sched_power_savings < POWERSAVINGS_MAX)
return 0;
}

@@ -4739,7 +4740,7 @@ static struct {
unsigned long next_balance; /* in jiffy units */
} nohz ____cacheline_aligned;

-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+#ifdef CONFIG_SCHED_POWERSAVE
/**
* lowest_flag_domain - Return lowest sched_domain containing flag.
* @cpu: The cpu whose lowest level of sched domain is to
@@ -4796,7 +4797,7 @@ static int find_new_ilb(int cpu)
* Have idle load balancer selection from semi-idle packages only
* when power-aware load balancing is enabled
*/
- if (!(sched_smt_power_savings || sched_mc_power_savings))
+ if (!(sched_power_savings))
goto out_done;

/*
@@ -4831,7 +4832,7 @@ out_done:

return nr_cpu_ids;
}
-#else /* (CONFIG_SCHED_MC || CONFIG_SCHED_SMT) */
+#else /* (CONFIG_SCHED_POWERSAVE) */
static inline int find_new_ilb(int call_cpu)
{
return nr_cpu_ids;

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