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Date: Mon, 22 Feb 2010 19:50:18 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Suresh Siddha <suresh.b.siddha@...el.com>
Cc: Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
"Ma, Ling" <ling.ma@...el.com>,
"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
"ego@...ibm.com" <ego@...ibm.com>,
"svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com>
Subject: Re: change in sched cpu_power causing regressions with SCHED_MC
On Fri, 2010-02-19 at 17:13 -0800, Suresh Siddha wrote:
> Ok Peter. There is another place that is scaling load_per_task with
> cpu_power but later comparing with the difference of max and min of the
> actual cpu load. :(
>
> avg_load_per_task = (sum_avg_load_per_task * SCHED_LOAD_SCALE) /
> group->cpu_power;
>
> if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
> sgs->group_imb = 1;
>
> Fixing this seems to have fixed the problem you mentioned. Can you
> please checkout the appended patch? If everything seems ok, then I will
> send the patch (against -tip tree) on monday morning with the detailed
> changelog.
Yes, this one does seem to generate the intended behaviour and does look
good (after cleaning up some of the now redundant comments).
Thanks!
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 3a8fb30..213b445 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3423,6 +3423,7 @@ struct sd_lb_stats {
> unsigned long max_load;
> unsigned long busiest_load_per_task;
> unsigned long busiest_nr_running;
> + unsigned long busiest_group_capacity;
>
> int group_imb; /* Is there imbalance in this sd */
> #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
> @@ -3742,8 +3743,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
> unsigned long load, max_cpu_load, min_cpu_load;
> int i;
> unsigned int balance_cpu = -1, first_idle_cpu = 0;
> - unsigned long sum_avg_load_per_task;
> - unsigned long avg_load_per_task;
> + unsigned long avg_load_per_task = 0;
>
> if (local_group) {
> balance_cpu = group_first_cpu(group);
> @@ -3752,7 +3752,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
> }
>
> /* Tally up the load of all CPUs in the group */
> - sum_avg_load_per_task = avg_load_per_task = 0;
> max_cpu_load = 0;
> min_cpu_load = ~0UL;
>
> @@ -3782,7 +3781,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
> sgs->sum_nr_running += rq->nr_running;
> sgs->sum_weighted_load += weighted_cpuload(i);
>
> - sum_avg_load_per_task += cpu_avg_load_per_task(i);
> }
>
> /*
> @@ -3801,6 +3799,9 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
> sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;
>
>
> + if (sgs->sum_nr_running)
> + avg_load_per_task =
> + sgs->sum_weighted_load / sgs->sum_nr_running;
> /*
> * Consider the group unbalanced when the imbalance is larger
> * than the average weight of two tasks.
> @@ -3810,9 +3811,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
> * normalized nr_running number somewhere that negates
> * the hierarchy?
> */
> - avg_load_per_task = (sum_avg_load_per_task * SCHED_LOAD_SCALE) /
> - group->cpu_power;
> -
> if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
> sgs->group_imb = 1;
>
> @@ -3880,6 +3878,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
> sds->max_load = sgs.avg_load;
> sds->busiest = group;
> sds->busiest_nr_running = sgs.sum_nr_running;
> + sds->busiest_group_capacity = sgs.group_capacity;
> sds->busiest_load_per_task = sgs.sum_weighted_load;
> sds->group_imb = sgs.group_imb;
> }
> @@ -3902,6 +3901,7 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
> {
> unsigned long tmp, pwr_now = 0, pwr_move = 0;
> unsigned int imbn = 2;
> + unsigned long scaled_busy_load_per_task;
>
> if (sds->this_nr_running) {
> sds->this_load_per_task /= sds->this_nr_running;
> @@ -3912,8 +3912,12 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
> sds->this_load_per_task =
> cpu_avg_load_per_task(this_cpu);
>
> - if (sds->max_load - sds->this_load + sds->busiest_load_per_task >=
> - sds->busiest_load_per_task * imbn) {
> + scaled_busy_load_per_task = sds->busiest_load_per_task
> + * SCHED_LOAD_SCALE;
> + scaled_busy_load_per_task /= sds->busiest->cpu_power;
> +
> + if (sds->max_load - sds->this_load + scaled_busy_load_per_task >=
> + (scaled_busy_load_per_task * imbn)) {
> *imbalance = sds->busiest_load_per_task;
> return;
> }
> @@ -3964,7 +3968,7 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
> static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
> unsigned long *imbalance)
> {
> - unsigned long max_pull;
> + unsigned long max_pull, load_above_capacity = ~0UL;
> /*
> * In the presence of smp nice balancing, certain scenarios can have
> * max load less than avg load(as we skip the groups at or below
> @@ -3975,9 +3979,30 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
> return fix_small_imbalance(sds, this_cpu, imbalance);
> }
>
> - /* Don't want to pull so many tasks that a group would go idle */
> - max_pull = min(sds->max_load - sds->avg_load,
> - sds->max_load - sds->busiest_load_per_task);
> + if (!sds->group_imb) {
> + /*
> + * Don't want to pull so many tasks that a group would go idle.
> + */
> + load_above_capacity = (sds->busiest_nr_running -
> + sds->busiest_group_capacity);
> +
> + load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_LOAD_SCALE);
> +
> + load_above_capacity /= sds->busiest->cpu_power;
> + }
> +
> + /*
> + * We're trying to get all the cpus to the average_load, so we don't
> + * want to push ourselves above the average load, nor do we wish to
> + * reduce the max loaded cpu below the average load, as either of these
> + * actions would just result in more rebalancing later, and ping-pong
> + * tasks around. Thus we look for the minimum possible imbalance.
> + * Negative imbalances (*we* are more loaded than anyone else) will
> + * be counted as no imbalance for these purposes -- we can't fix that
> + * by pulling tasks to us. Be careful of negative numbers as they'll
> + * appear as very large values with unsigned longs.
> + */
> + max_pull = min(sds->max_load - sds->avg_load, load_above_capacity);
>
> /* How much load to actually move to equalise the imbalance */
> *imbalance = min(max_pull * sds->busiest->cpu_power,
> @@ -4069,19 +4094,6 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
> sds.busiest_load_per_task =
> min(sds.busiest_load_per_task, sds.avg_load);
>
> - /*
> - * We're trying to get all the cpus to the average_load, so we don't
> - * want to push ourselves above the average load, nor do we wish to
> - * reduce the max loaded cpu below the average load, as either of these
> - * actions would just result in more rebalancing later, and ping-pong
> - * tasks around. Thus we look for the minimum possible imbalance.
> - * Negative imbalances (*we* are more loaded than anyone else) will
> - * be counted as no imbalance for these purposes -- we can't fix that
> - * by pulling tasks to us. Be careful of negative numbers as they'll
> - * appear as very large values with unsigned longs.
> - */
> - if (sds.max_load <= sds.busiest_load_per_task)
> - goto out_balanced;
>
> /* Looks like there is an imbalance. Compute it */
> calculate_imbalance(&sds, this_cpu, imbalance);
>
>
>
>
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