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Date: Fri, 2 Aug 2013 18:08:52 +0900
From: Joonsoo Kim <iamjoonsoo.kim@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
Alex Shi <alex.shi@...el.com>,
Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
Morten Rasmussen <morten.rasmussen@....com>,
Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v2 2/3] sched: factor out code to should_we_balance()
On Fri, Aug 02, 2013 at 09:51:45AM +0200, Vincent Guittot wrote:
> On 2 August 2013 03:50, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> > 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 @should_balance in order to represent
> > its purpose more clearly.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index eaae77e..7f51b8c 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4426,22 +4426,17 @@ 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;
> > @@ -4454,15 +4449,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> > nr_running = rq->nr_running;
> >
> > /* 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;
> > - }
> > -
> > + if (local_group)
> > load = target_load(i, load_idx);
> > - } else {
> > + else {
> > load = source_load(i, load_idx);
> > if (load > max_cpu_load)
> > max_cpu_load = load;
> > @@ -4482,22 +4471,9 @@ 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;
> > - }
> > - 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);
> > - }
> > + if (local_group && (env->idle != CPU_NEWLY_IDLE ||
> > + 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;
> > @@ -4576,7 +4552,7 @@ 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;
> > @@ -4593,10 +4569,7 @@ 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;
> > @@ -4829,8 +4802,6 @@ 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,
> > @@ -4838,7 +4809,7 @@ 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;
> >
> > @@ -4848,14 +4819,7 @@ 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))
> > @@ -4919,7 +4883,6 @@ force_balance:
> > return sds.busiest;
> >
> > out_balanced:
> > -ret:
> > env->imbalance = 0;
> > return NULL;
> > }
> > @@ -5001,13 +4964,47 @@ 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 *should_balance)
> > {
> > int ld_moved, cur_ld_moved, active_balance = 0;
> > struct sched_group *group;
> > @@ -5036,12 +5033,14 @@ 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)) {
> > + *should_balance = 0;
> > goto out_balanced;
> > + } else
> > + *should_balance = 1;
> >
> > +redo:
> > + group = find_busiest_group(&env);
> > if (!group) {
> > schedstat_inc(sd, lb_nobusyg[idle]);
> > goto out_balanced;
> > @@ -5254,7 +5253,7 @@ 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 should_balance;
> >
> > if (!(sd->flags & SD_LOAD_BALANCE))
> > continue;
> > @@ -5262,7 +5261,8 @@ 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,
> > + &should_balance);
> > }
> >
> > interval = msecs_to_jiffies(sd->balance_interval);
> > @@ -5502,7 +5502,7 @@ void update_max_interval(void)
> > */
> > static void rebalance_domains(int cpu, enum cpu_idle_type idle)
> > {
> > - int balance = 1;
> > + int should_balance;
>
> int should_balance = 1;
> because if (time_after_eq(jiffies, sd->last_balance + interval)) can
> skip the 1st load_balance and you will test should_balance with its
> initial value.
Hello, Vincent.
Yes, you are right.
I will fix it.
Thanks.
>
> Vincent
>
> > struct rq *rq = cpu_rq(cpu);
> > unsigned long interval;
> > struct sched_domain *sd;
> > @@ -5534,7 +5534,7 @@ 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, &should_balance)) {
> > /*
> > * The LBF_SOME_PINNED logic could have changed
> > * env->dst_cpu, so we can't know our idle
> > @@ -5557,7 +5557,7 @@ out:
> > * CPU in our sched group which is doing load balancing more
> > * actively.
> > */
> > - if (!balance)
> > + if (!should_balance)
> > break;
> > }
> > rcu_read_unlock();
> > --
> > 1.7.9.5
> >
> --
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