From 118de48b5183dbb3d6281302528ad1a93624854f Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Thu, 10 Feb 2011 10:23:28 +0100 Subject: [PATCH] sched: Use group weight, idle cpu metrics to fix imbalances during idle Commit: aae6d3ddd8b90f5b2c8d79a2b914d1706d124193 upstream Currently we consider a sched domain to be well balanced when the imbalance is less than the domain's imablance_pct. As the number of cores and threads are increasing, current values of imbalance_pct (for example 25% for a NUMA domain) are not enough to detect imbalances like: a) On a WSM-EP system (two sockets, each having 6 cores and 12 logical threads), 24 cpu-hogging tasks get scheduled as 13 on one socket and 11 on another socket. Leading to an idle HT cpu. b) On a hypothetial 2 socket NHM-EX system (each socket having 8 cores and 16 logical threads), 16 cpu-hogging tasks can get scheduled as 9 on one socket and 7 on another socket. Leaving one core in a socket idle whereas in another socket we have a core having both its HT siblings busy. While this issue can be fixed by decreasing the domain's imbalance_pct (by making it a function of number of logical cpus in the domain), it can potentially cause more task migrations across sched groups in an overloaded case. Fix this by using imbalance_pct only during newly_idle and busy load balancing. And during idle load balancing, check if there is an imbalance in number of idle cpu's across the busiest and this sched_group or if the busiest group has more tasks than its weight that the idle cpu in this_group can pull. Reported-by: Nikhil Rao Signed-off-by: Suresh Siddha Signed-off-by: Peter Zijlstra Signed-off-by: Andi Kleen LKML-Reference: <1284760952.2676.11.camel@sbsiddha-MOBL3.sc.intel.com> Signed-off-by: Ingo Molnar Signed-off-by: Mike Galbraith Acked-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- include/linux/sched.h | 1 + kernel/sched.c | 2 ++ kernel/sched_fair.c | 34 +++++++++++++++++++++++++++++++--- 3 files changed, 34 insertions(+), 3 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 0c2e5b5d02cc..fc531a780124 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -856,6 +856,7 @@ struct sched_group { * single CPU. */ unsigned int cpu_power; + unsigned int group_weight; /* * The CPUs this group covers. diff --git a/kernel/sched.c b/kernel/sched.c index 82f64af45d28..772b2d53cedb 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -6839,6 +6839,8 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd) if (cpu != group_first_cpu(sd->groups)) return; + sd->groups->group_weight = cpumask_weight(sched_group_cpus(sd->groups)); + child = sd->child; sd->groups->cpu_power = 0; diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 38ca32a60682..09a98114ec32 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -2036,13 +2036,16 @@ struct sd_lb_stats { unsigned long this_load_per_task; unsigned long this_nr_running; unsigned long this_has_capacity; + unsigned int this_idle_cpus; /* Statistics of the busiest group */ + unsigned int busiest_idle_cpus; unsigned long max_load; unsigned long busiest_load_per_task; unsigned long busiest_nr_running; unsigned long busiest_group_capacity; unsigned long busiest_has_capacity; + unsigned int busiest_group_weight; int group_imb; /* Is there imbalance in this sd */ #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT) @@ -2064,6 +2067,8 @@ struct sg_lb_stats { unsigned long sum_nr_running; /* Nr tasks running in the group */ unsigned long sum_weighted_load; /* Weighted load of group's tasks */ unsigned long group_capacity; + unsigned long idle_cpus; + unsigned long group_weight; int group_imb; /* Is there an imbalance in the group ? */ int group_has_capacity; /* Is there extra capacity in the group? */ }; @@ -2404,7 +2409,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd, sgs->group_load += load; sgs->sum_nr_running += rq->nr_running; sgs->sum_weighted_load += weighted_cpuload(i); - + if (idle_cpu(i)) + sgs->idle_cpus++; } /* @@ -2440,6 +2446,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd, sgs->group_imb = 1; sgs->group_capacity = DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE); + sgs->group_weight = group->group_weight; if (sgs->group_capacity > sgs->sum_nr_running) sgs->group_has_capacity = 1; @@ -2505,13 +2512,16 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu, sds->this_nr_running = sgs.sum_nr_running; sds->this_load_per_task = sgs.sum_weighted_load; sds->this_has_capacity = sgs.group_has_capacity; + sds->this_idle_cpus = sgs.idle_cpus; } else if (sgs.avg_load > sds->max_load && (sgs.sum_nr_running > sgs.group_capacity || sgs.group_imb)) { sds->max_load = sgs.avg_load; sds->busiest = group; sds->busiest_nr_running = sgs.sum_nr_running; + sds->busiest_idle_cpus = sgs.idle_cpus; sds->busiest_group_capacity = sgs.group_capacity; + sds->busiest_group_weight = sgs.group_weight; sds->busiest_load_per_task = sgs.sum_weighted_load; sds->busiest_has_capacity = sgs.group_has_capacity; sds->group_imb = sgs.group_imb; @@ -2736,8 +2746,26 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, if (sds.this_load >= sds.avg_load) goto out_balanced; - if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load) - goto out_balanced; + /* + * In the CPU_NEWLY_IDLE, use imbalance_pct to be conservative. + * And to check for busy balance use !idle_cpu instead of + * CPU_NOT_IDLE. This is because HT siblings will use CPU_NOT_IDLE + * even when they are idle. + */ + if (idle == CPU_NEWLY_IDLE || !idle_cpu(this_cpu)) { + if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load) + goto out_balanced; + } else { + /* + * This cpu is idle. If the busiest group load doesn't + * have more tasks than the number of available cpu's and + * there is no imbalance between this and busiest group + * wrt to idle cpu's, it is balanced. + */ + if ((sds.this_idle_cpus <= sds.busiest_idle_cpus + 1) && + sds.busiest_nr_running <= sds.busiest_group_weight) + goto out_balanced; + } force_balance: /* Looks like there is an imbalance. Compute it */ -- 2.39.2