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Subject[RFC PATCH 10/11] sched: Refactor the power savings balance code.
Date
Create seperate helper functions to initialize the power-savings-balance
related variables, to update them and to check if we have a scope for
performing power-savings balance.

Add no-op inline functions for the !(CONFIG_SCHED_MC || CONFIG_SCHED_SMT)
case.
This will eliminate all the #ifdef jungle in find_busiest_group() and the
other helper functions.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
---
kernel/sched.c | 236 ++++++++++++++++++++++++++++++++++++--------------------
1 files changed, 153 insertions(+), 83 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index cb2c97b..6404ddf 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3166,6 +3166,151 @@ static inline int get_sd_load_idx(struct sched_domain *sd,
}


+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+/**
+ * init_sd_power_savings_stats - Initialize power savings statistics for
+ * the given sched_domain, during load balancing.
+ *
+ * @sd: Sched domain whose power-savings statistics are to be initialized.
+ * @sds: Variable containing the statistics for sd.
+ * @idle: Idle status of the CPU at which we're performing load-balancing.
+ */
+static inline void init_sd_power_savings_stats(struct sched_domain *sd,
+ struct sd_lb_stats *sds, enum cpu_idle_type idle)
+{
+ /*
+ * Busy processors will not participate in power savings
+ * balance.
+ */
+ if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+ sds->power_savings_balance = 0;
+ else {
+ sds->power_savings_balance = 1;
+ sds->min_nr_running = ULONG_MAX;
+ sds->leader_nr_running = 0;
+ }
+}
+
+/**
+ * update_sd_power_savings_stats - Update the power saving stats for a
+ * sched_domain while performing load balancing.
+ *
+ * @group: sched_group belonging to the sched_domain under consideration.
+ * @sds: Variable containing the statistics of the sched_domain
+ * @local_group: Does group contain the CPU for which we're performing
+ * load balancing ?
+ * @sgs: Variable containing the statistics of the group.
+ */
+static inline void update_sd_power_savings_stats(struct sched_group *group,
+ struct sd_lb_stats *sds, int local_group, struct sg_lb_stats *sgs)
+{
+
+ if (!sds->power_savings_balance)
+ return;
+
+ /*
+ * If the local group is idle or completely loaded
+ * no need to do power savings balance at this domain
+ */
+ if (local_group && (sds->this_nr_running >= sgs->group_capacity ||
+ !sds->this_nr_running))
+ sds->power_savings_balance = 0;
+
+ /*
+ * If a group is already running at full capacity or idle,
+ * don't include that group in power savings calculations
+ */
+ if (!sds->power_savings_balance ||
+ sgs->sum_nr_running >= sgs->group_capacity ||
+ !sgs->sum_nr_running)
+ return;
+
+ /*
+ * Calculate the group which has the least non-idle load.
+ * This is the group from where we need to pick up the load
+ * for saving power
+ */
+ if ((sgs->sum_nr_running < sds->min_nr_running) ||
+ (sgs->sum_nr_running == sds->min_nr_running &&
+ group_first_cpu(group) > group_first_cpu(sds->group_min))) {
+ sds->group_min = group;
+ sds->min_nr_running = sgs->sum_nr_running;
+ sds->min_load_per_task = sgs->sum_weighted_load /
+ sgs->sum_nr_running;
+ }
+
+ /*
+ * Calculate the group which is almost near its
+ * capacity but still has some space to pick up some load
+ * from other group and save more power
+ */
+ if (sgs->sum_nr_running > sgs->group_capacity - 1)
+ return;
+
+ if (sgs->sum_nr_running > sds->leader_nr_running ||
+ (sgs->sum_nr_running == sds->leader_nr_running &&
+ group_first_cpu(group) < group_first_cpu(sds->group_leader))) {
+ sds->group_leader = group;
+ sds->leader_nr_running = sgs->sum_nr_running;
+ }
+}
+
+/**
+ * check_power_save_busiest_group - Check if we have potential to perform
+ * some power-savings balance. If yes, set the busiest group to be
+ * the least loaded group in the sched_domain, so that it's CPUs can
+ * be put to idle.
+ *
+ * @sds: Variable containing the statistics of the sched_domain
+ * under consideration.
+ * @this_cpu: Cpu at which we're currently performing load-balancing.
+ * @imbalance: Variable to store the imbalance.
+ *
+ * Returns 1 if there is potential to perform power-savings balance.
+ * Else returns 0.
+ */
+static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
+ int this_cpu, unsigned long *imbalance)
+{
+ if (!sds->power_savings_balance)
+ return 0;
+
+ if (sds->this != sds->group_leader ||
+ sds->group_leader == sds->group_min)
+ return 0;
+
+ *imbalance = sds->min_load_per_task;
+ sds->busiest = sds->group_min;
+
+ if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
+ cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
+ group_first_cpu(sds->group_leader);
+ }
+
+ return 1;
+
+}
+#else /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+static inline void init_sd_power_savings_stats(struct sched_domain *sd,
+ struct sd_lb_stats *sds, enum cpu_idle_type idle)
+{
+ return;
+}
+
+static inline void update_sd_power_savings_stats(struct sched_group *group,
+ struct sd_lb_stats *sds, int local_group, struct sg_lb_stats *sgs)
+{
+ return;
+}
+
+static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
+ int this_cpu, unsigned long *imbalance)
+{
+ return 0;
+}
+#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+
+
/**
* update_sg_lb_stats - Update sched_group's statistics for load balancing.
* @group: sched_group whose statistics are to be updated.
@@ -3281,19 +3426,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
struct sg_lb_stats sgs;
int load_idx;

-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
- /*
- * Busy processors will not participate in power savings
- * balance.
- */
- if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
- sds->power_savings_balance = 0;
- else {
- sds->power_savings_balance = 1;
- sds->min_nr_running = ULONG_MAX;
- sds->leader_nr_running = 0;
- }
-#endif
+ init_sd_power_savings_stats(sd, sds, idle);
load_idx = get_sd_load_idx(sd, idle);

do {
@@ -3326,61 +3459,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
sds->group_imb = sgs.group_imb;
}

-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-
- if (!sds->power_savings_balance)
- goto group_next;
-
- /*
- * If the local group is idle or completely loaded
- * no need to do power savings balance at this domain
- */
- if (local_group &&
- (sds->this_nr_running >= sgs.group_capacity ||
- !sds->this_nr_running))
- sds->power_savings_balance = 0;
-
- /*
- * If a group is already running at full capacity or idle,
- * don't include that group in power savings calculations
- */
- if (!sds->power_savings_balance ||
- sgs.sum_nr_running >= sgs.group_capacity ||
- !sgs.sum_nr_running)
- goto group_next;
-
- /*
- * Calculate the group which has the least non-idle load.
- * This is the group from where we need to pick up the load
- * for saving power
- */
- if ((sgs.sum_nr_running < sds->min_nr_running) ||
- (sgs.sum_nr_running == sds->min_nr_running &&
- group_first_cpu(group) >
- group_first_cpu(sds->group_min))) {
- sds->group_min = group;
- sds->min_nr_running = sgs.sum_nr_running;
- sds->min_load_per_task = sgs.sum_weighted_load /
- sgs.sum_nr_running;
- }
-
- /*
- * Calculate the group which is almost near its
- * capacity but still has some space to pick up some load
- * from other group and save more power
- */
- if (sgs.sum_nr_running > sgs.group_capacity - 1)
- goto group_next;
-
- if (sgs.sum_nr_running > sds->leader_nr_running ||
- (sgs.sum_nr_running == sds->leader_nr_running &&
- group_first_cpu(group) <
- group_first_cpu(sds->group_leader))) {
- sds->group_leader = group;
- sds->leader_nr_running = sgs.sum_nr_running;
- }
-group_next:
-#endif
+ update_sd_power_savings_stats(group, sds, local_group, &sgs);
group = group->next;
} while (group != sd->groups);

@@ -3551,21 +3630,12 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
return sds.busiest;

out_balanced:
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
- if (!sds.power_savings_balance)
- goto ret;
-
- if (sds.this != sds.group_leader || sds.group_leader == sds.group_min)
- goto ret;
-
- *imbalance = sds.min_load_per_task;
- if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
- cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
- group_first_cpu(sds.group_leader);
- }
- return sds.group_min;
-
-#endif
+ /*
+ * There is no obvious imbalance. But check if we can do some balancing
+ * to save power.
+ */
+ if (check_power_save_busiest_group(&sds, this_cpu, imbalance))
+ return sds.busiest;
ret:
*imbalance = 0;
return NULL;


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