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sched: Factor out code to should_we_balance()

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Now checking whether this cpu is appropriate to balance or not
is embedded into update_sg_lb_stats() and this checking has no direct
relationship to this function. There is not enough reason to place
this checking at update_sg_lb_stats(), except saving one iteration
for sched_group_cpus.

In this patch, I factor out this checking to should_we_balance() function.
And before doing actual work for load_balancing, check whether this cpu is
appropriate to balance via should_we_balance(). If this cpu is not
a candidate for balancing, it quit the work immediately.

With this change, we can save two memset cost and can expect better
compiler optimization.

Below is result of this patch.

 * Vanilla *
   text	   data	    bss	    dec	    hex	filename
  34499	   1136	    116	  35751	   8ba7	kernel/sched/fair.o

 * Patched *
   text	   data	    bss	    dec	    hex	filename
  34243	   1136	    116	  35495	   8aa7	kernel/sched/fair.o

In addition, rename @balance to @continue_balancing in order to represent
its purpose more clearly.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
[ s/should_balance/continue_balancing/g ]
Reviewed-by: Paul Turner <pjt@google.com>
[ Made style changes and a fix in should_we_balance(). ]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1375778203-31343-3-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Joonsoo Kim 2013-08-06 17:36:42 +09:00 committed by Ingo Molnar
parent 95a79b805b
commit 23f0d2093c
1 changed files with 53 additions and 54 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

105
kernel/sched/fair.c
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@ -4463,22 +4463,17 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
* @group: sched_group whose statistics are to be updated.
* @load_idx: Load index of sched_domain of this_cpu for load calc.
* @local_group: Does group contain this_cpu.
* @balance: Should we balance.
* @sgs: variable to hold the statistics for this group.
*/
static inline void update_sg_lb_stats(struct lb_env *env,
struct sched_group *group, int load_idx,
int local_group, int *balance, struct sg_lb_stats *sgs)
int local_group, struct sg_lb_stats *sgs)
{
unsigned long nr_running, max_nr_running, min_nr_running;
unsigned long load, max_cpu_load, min_cpu_load;
unsigned int balance_cpu = -1, first_idle_cpu = 0;
unsigned long avg_load_per_task = 0;
int i;
if (local_group)
balance_cpu = group_balance_cpu(group);
/* Tally up the load of all CPUs in the group */
max_cpu_load = 0;
min_cpu_load = ~0UL;
@ -4492,12 +4487,6 @@ static inline void update_sg_lb_stats(struct lb_env *env,
/* Bias balancing toward cpus of our domain */
if (local_group) {
if (idle_cpu(i) && !first_idle_cpu &&
cpumask_test_cpu(i, sched_group_mask(group))) {
first_idle_cpu = 1;
balance_cpu = i;
}
load = target_load(i, load_idx);
} else {
load = source_load(i, load_idx);
@ -4519,22 +4508,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
sgs->idle_cpus++;
}
/*
* First idle cpu or the first cpu(busiest) in this sched group
* is eligible for doing load balancing at this and above
* domains. In the newly idle case, we will allow all the cpu's
* to do the newly idle load balance.
*/
if (local_group) {
if (env->idle != CPU_NEWLY_IDLE) {
if (balance_cpu != env->dst_cpu) {
*balance = 0;
return;
}
if (local_group && (env->idle != CPU_NEWLY_IDLE ||
time_after_eq(jiffies, group->sgp->next_update)))
update_group_power(env->sd, env->dst_cpu);
} else if (time_after_eq(jiffies, group->sgp->next_update))
update_group_power(env->sd, env->dst_cpu);
}
/* Adjust by relative CPU power of the group */
sgs->avg_load = (sgs->group_load*SCHED_POWER_SCALE) / group->sgp->power;
@ -4613,7 +4589,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
* @sds: variable to hold the statistics for this sched_domain.
*/
static inline void update_sd_lb_stats(struct lb_env *env,
int *balance, struct sd_lb_stats *sds)
struct sd_lb_stats *sds)
{
struct sched_domain *child = env->sd->child;
struct sched_group *sg = env->sd->groups;
@ -4630,10 +4606,7 @@ static inline void update_sd_lb_stats(struct lb_env *env,
local_group = cpumask_test_cpu(env->dst_cpu, sched_group_cpus(sg));
memset(&sgs, 0, sizeof(sgs));
update_sg_lb_stats(env, sg, load_idx, local_group, balance, &sgs);
if (local_group && !(*balance))
return;
update_sg_lb_stats(env, sg, load_idx, local_group, &sgs);
sds->total_load += sgs.group_load;
sds->total_pwr += sg->sgp->power;
@ -4866,8 +4839,6 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
* to restore balance.
*
* @env: The load balancing environment.
* @balance: Pointer to a variable indicating if this_cpu
* is the appropriate cpu to perform load balancing at this_level.
*
* Returns: - the busiest group if imbalance exists.
* - If no imbalance and user has opted for power-savings balance,
@ -4875,7 +4846,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
* put to idle by rebalancing its tasks onto our group.
*/
static struct sched_group *
find_busiest_group(struct lb_env *env, int *balance)
find_busiest_group(struct lb_env *env)
{
struct sd_lb_stats sds;
@ -4885,14 +4856,7 @@ find_busiest_group(struct lb_env *env, int *balance)
* Compute the various statistics relavent for load balancing at
* this level.
*/
update_sd_lb_stats(env, balance, &sds);
/*
* this_cpu is not the appropriate cpu to perform load balancing at
* this level.
*/
if (!(*balance))
goto ret;
update_sd_lb_stats(env, &sds);
if ((env->idle == CPU_IDLE || env->idle == CPU_NEWLY_IDLE) &&
check_asym_packing(env, &sds))
@ -4956,7 +4920,6 @@ force_balance:
return sds.busiest;
out_balanced:
ret:
env->imbalance = 0;
return NULL;
}
@ -5043,13 +5006,47 @@ static int need_active_balance(struct lb_env *env)
static int active_load_balance_cpu_stop(void *data);
static int should_we_balance(struct lb_env *env)
{
struct sched_group *sg = env->sd->groups;
struct cpumask *sg_cpus, *sg_mask;
int cpu, balance_cpu = -1;
/*
* In the newly idle case, we will allow all the cpu's
* to do the newly idle load balance.
*/
if (env->idle == CPU_NEWLY_IDLE)
return 1;
sg_cpus = sched_group_cpus(sg);
sg_mask = sched_group_mask(sg);
/* Try to find first idle cpu */
for_each_cpu_and(cpu, sg_cpus, env->cpus) {
if (!cpumask_test_cpu(cpu, sg_mask) || !idle_cpu(cpu))
continue;
balance_cpu = cpu;
break;
}
if (balance_cpu == -1)
balance_cpu = group_balance_cpu(sg);
/*
* First idle cpu or the first cpu(busiest) in this sched group
* is eligible for doing load balancing at this and above domains.
*/
return balance_cpu != env->dst_cpu;
}
/*
* Check this_cpu to ensure it is balanced within domain. Attempt to move
* tasks if there is an imbalance.
*/
static int load_balance(int this_cpu, struct rq *this_rq,
struct sched_domain *sd, enum cpu_idle_type idle,
int *balance)
int *continue_balancing)
{
int ld_moved, cur_ld_moved, active_balance = 0;
struct sched_group *group;
@ -5079,11 +5076,12 @@ static int load_balance(int this_cpu, struct rq *this_rq,
schedstat_inc(sd, lb_count[idle]);
redo:
group = find_busiest_group(&env, balance);
if (*balance == 0)
if (!should_we_balance(&env)) {
*continue_balancing = 0;
goto out_balanced;
}
group = find_busiest_group(&env);
if (!group) {
schedstat_inc(sd, lb_nobusyg[idle]);
goto out_balanced;
@ -5296,7 +5294,7 @@ void idle_balance(int this_cpu, struct rq *this_rq)
rcu_read_lock();
for_each_domain(this_cpu, sd) {
unsigned long interval;
int balance = 1;
int continue_balancing = 1;
if (!(sd->flags & SD_LOAD_BALANCE))
continue;
@ -5304,7 +5302,8 @@ void idle_balance(int this_cpu, struct rq *this_rq)
if (sd->flags & SD_BALANCE_NEWIDLE) {
/* If we've pulled tasks over stop searching: */
pulled_task = load_balance(this_cpu, this_rq,
sd, CPU_NEWLY_IDLE, &balance);
sd, CPU_NEWLY_IDLE,
&continue_balancing);
}
interval = msecs_to_jiffies(sd->balance_interval);
@ -5542,7 +5541,7 @@ void update_max_interval(void)
*/
static void rebalance_domains(int cpu, enum cpu_idle_type idle)
{
int balance = 1;
int continue_balancing = 1;
struct rq *rq = cpu_rq(cpu);
unsigned long interval;
struct sched_domain *sd;
@ -5574,7 +5573,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
}
if (time_after_eq(jiffies, sd->last_balance + interval)) {
if (load_balance(cpu, rq, sd, idle, &balance)) {
if (load_balance(cpu, rq, sd, idle, &continue_balancing)) {
/*
* The LBF_SOME_PINNED logic could have changed
* env->dst_cpu, so we can't know our idle
@ -5597,7 +5596,7 @@ out:
* CPU in our sched group which is doing load balancing more
* actively.
*/
if (!balance)
if (!continue_balancing)
break;
}
rcu_read_unlock();