On 08/02/2013 02:35 PM, 김준수 wrote: > > >> -----Original Message----- >> From: Preeti U Murthy [mailto:pre...@linux.vnet.ibm.com] >> Sent: Friday, August 02, 2013 1:23 PM >> To: Joonsoo Kim >> Cc: Ingo Molnar; Peter Zijlstra; linux-kernel@vger.kernel.org; Mike >> Galbraith; Paul Turner; Alex Shi; Vincent Guittot; Morten Rasmussen; >> Namhyung Kim; Joonsoo Kim >> Subject: Re: [PATCH v2 2/3] sched: factor out code to should_we_balance() >> >> Hi Joonsoo, > > Hello, Preeti. > >> >> On 08/02/2013 07:20 AM, Joonsoo Kim 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....@lge.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); >>> - } >> >> Observe what is happening in the above code which checks if we should >> balance on the env->dst_cpu. >> >> Only if the env->dst_cpu "belongs" to the group considered in >> update_sg_lb_stats(), which means local_group = 1,should the above checks >> be carried out. >> >> Meaning, if there is a better CPU in the same group to which >> env->dst_cpu belongs, to carry out load balancing for the system (in the >> above case, balance_cpu), cancel the current iteration of load balancing >> on env->dst_cpu. Wait for the right cpu in this group to do the load >> balancing. >> >> Keeping this in mind see the below comments around should_we_balance(). > > Okay. > >> >>> @@ -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; >>> + } >> >> You need to iterate over all the groups of the sched domain env->sd and >> not just the first group of env->sd like you are doing above. This is to > > I don't think so. > IIRC, env->sd->groups always means local group, > so we don't need to find our group by iterating over all the groups.
Take a look at update_sd_lb_stats(). That should clarify this. There is an exclusive local_group check there. sd->groups points to the first group in the list of groups under this sd. Regards Preeti U Murthy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
