From: Joonsoo Kim 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 [peterz: style changes and a fix in should_we_balance() ] Signed-off-by: Peter Zijlstra --- kernel/sched/fair.c | 111 +++++++++++++++++++++++++--------------------------- 1 file changed, 54 insertions(+), 57 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4510,22 +4510,17 @@ fix_small_capacity(struct sched_domain * * @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; @@ -4538,15 +4533,9 @@ static inline void update_sg_lb_stats(st 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; @@ -4566,22 +4555,9 @@ static inline void update_sg_lb_stats(st 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; @@ -4663,7 +4639,7 @@ static bool update_sd_pick_busiest(struc * @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; @@ -4680,10 +4656,7 @@ static inline void update_sd_lb_stats(st 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; @@ -4916,8 +4889,6 @@ static inline void calculate_imbalance(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. * * Return: - The busiest group if imbalance exists. * - If no imbalance and user has opted for power-savings balance, @@ -4925,7 +4896,7 @@ static inline void calculate_imbalance(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; @@ -4935,14 +4906,7 @@ find_busiest_group(struct lb_env *env, i * 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)) @@ -5006,7 +4970,6 @@ find_busiest_group(struct lb_env *env, i return sds.busiest; out_balanced: -ret: env->imbalance = 0; return NULL; } @@ -5088,13 +5051,47 @@ static int need_active_balance(struct lb 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; @@ -5123,12 +5120,11 @@ static int load_balance(int this_cpu, st schedstat_inc(sd, lb_count[idle]); -redo: - group = find_busiest_group(&env, balance); - - if (*balance == 0) + if (!(*should_balance = should_we_balance(&env))) goto out_balanced; +redo: + group = find_busiest_group(&env); if (!group) { schedstat_inc(sd, lb_nobusyg[idle]); goto out_balanced; @@ -5340,7 +5336,7 @@ void idle_balance(int this_cpu, struct r 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; @@ -5348,7 +5344,8 @@ void idle_balance(int this_cpu, struct r 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); @@ -5586,7 +5583,7 @@ void update_max_interval(void) */ static void rebalance_domains(int cpu, enum cpu_idle_type idle) { - int balance = 1; + int should_balance = 1; struct rq *rq = cpu_rq(cpu); unsigned long interval; struct sched_domain *sd; @@ -5618,7 +5615,7 @@ static void rebalance_domains(int cpu, e } 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 @@ -5641,7 +5638,7 @@ static void rebalance_domains(int cpu, e * CPU in our sched group which is doing load balancing more * actively. */ - if (!balance) + if (!should_balance) break; } rcu_read_unlock(); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/