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sched: Fix SCHED_MC regression caused by change in sched cpu_power
On platforms like dual socket quad-core platform, the scheduler load
balancer is not detecting the load imbalances in certain scenarios. This
is leading to scenarios like where one socket is completely busy (with
all the 4 cores running with 4 tasks) and leaving another socket
completely idle. This causes performance issues as those 4 tasks share
the memory controller, last-level cache bandwidth etc. Also we won't be
taking advantage of turbo-mode as much as we would like, etc.
Some of the comparisons in the scheduler load balancing code are
comparing the "weighted cpu load that is scaled wrt sched_group's
cpu_power" with the "weighted average load per task that is not scaled
wrt sched_group's cpu_power". While this has probably been broken for a
longer time (for multi socket numa nodes etc), the problem got aggrevated
via this recent change:
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| commit f93e65c186
| Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
| Date: Tue Sep 1 10:34:32 2009 +0200
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| sched: Restore __cpu_power to a straight sum of power
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Also with this change, the sched group cpu power alone no longer reflects
the group capacity that is needed to implement MC, MT performance
(default) and power-savings (user-selectable) policies.
We need to use the computed group capacity (sgs.group_capacity, that is
computed using the SD_PREFER_SIBLING logic in update_sd_lb_stats()) to
find out if the group with the max load is above its capacity and how
much load to move etc.
Reported-by: Ma Ling <ling.ma@intel.com>
Initial-Analysis-by: Zhang, Yanmin <yanmin_zhang@linux.intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
[ -v2: build fix ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org> # [2.6.32.x, 2.6.33.x]
LKML-Reference: <1266970432.11588.22.camel@sbs-t61.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
parent
83ab0aa0d5
commit
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@ -2097,6 +2097,7 @@ struct sd_lb_stats {
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unsigned long max_load;
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unsigned long busiest_load_per_task;
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unsigned long busiest_nr_running;
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unsigned long busiest_group_capacity;
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int group_imb; /* Is there imbalance in this sd */
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#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
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@ -2416,14 +2417,12 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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unsigned long load, max_cpu_load, min_cpu_load;
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int i;
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unsigned int balance_cpu = -1, first_idle_cpu = 0;
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unsigned long sum_avg_load_per_task;
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unsigned long avg_load_per_task;
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unsigned long avg_load_per_task = 0;
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if (local_group)
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balance_cpu = group_first_cpu(group);
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/* Tally up the load of all CPUs in the group */
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sum_avg_load_per_task = avg_load_per_task = 0;
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max_cpu_load = 0;
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min_cpu_load = ~0UL;
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@ -2453,7 +2452,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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sgs->sum_nr_running += rq->nr_running;
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sgs->sum_weighted_load += weighted_cpuload(i);
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sum_avg_load_per_task += cpu_avg_load_per_task(i);
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}
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/*
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@ -2473,7 +2471,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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/* Adjust by relative CPU power of the group */
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sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;
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/*
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* Consider the group unbalanced when the imbalance is larger
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* than the average weight of two tasks.
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@ -2483,8 +2480,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
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* normalized nr_running number somewhere that negates
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* the hierarchy?
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*/
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avg_load_per_task = (sum_avg_load_per_task * SCHED_LOAD_SCALE) /
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group->cpu_power;
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if (sgs->sum_nr_running)
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avg_load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;
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if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
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sgs->group_imb = 1;
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@ -2553,6 +2550,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
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sds->max_load = sgs.avg_load;
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sds->busiest = group;
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sds->busiest_nr_running = sgs.sum_nr_running;
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sds->busiest_group_capacity = sgs.group_capacity;
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sds->busiest_load_per_task = sgs.sum_weighted_load;
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sds->group_imb = sgs.group_imb;
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}
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@ -2575,6 +2573,7 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
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{
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unsigned long tmp, pwr_now = 0, pwr_move = 0;
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unsigned int imbn = 2;
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unsigned long scaled_busy_load_per_task;
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if (sds->this_nr_running) {
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sds->this_load_per_task /= sds->this_nr_running;
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@ -2585,8 +2584,12 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
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sds->this_load_per_task =
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cpu_avg_load_per_task(this_cpu);
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if (sds->max_load - sds->this_load + sds->busiest_load_per_task >=
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sds->busiest_load_per_task * imbn) {
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scaled_busy_load_per_task = sds->busiest_load_per_task
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* SCHED_LOAD_SCALE;
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scaled_busy_load_per_task /= sds->busiest->cpu_power;
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if (sds->max_load - sds->this_load + scaled_busy_load_per_task >=
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(scaled_busy_load_per_task * imbn)) {
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*imbalance = sds->busiest_load_per_task;
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return;
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}
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@ -2637,7 +2640,14 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
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static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
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unsigned long *imbalance)
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{
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unsigned long max_pull;
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unsigned long max_pull, load_above_capacity = ~0UL;
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sds->busiest_load_per_task /= sds->busiest_nr_running;
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if (sds->group_imb) {
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sds->busiest_load_per_task =
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min(sds->busiest_load_per_task, sds->avg_load);
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}
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/*
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* In the presence of smp nice balancing, certain scenarios can have
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* max load less than avg load(as we skip the groups at or below
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@ -2648,9 +2658,29 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
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return fix_small_imbalance(sds, this_cpu, imbalance);
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}
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/* Don't want to pull so many tasks that a group would go idle */
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max_pull = min(sds->max_load - sds->avg_load,
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sds->max_load - sds->busiest_load_per_task);
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if (!sds->group_imb) {
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/*
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* Don't want to pull so many tasks that a group would go idle.
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*/
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load_above_capacity = (sds->busiest_nr_running -
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sds->busiest_group_capacity);
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load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_LOAD_SCALE);
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load_above_capacity /= sds->busiest->cpu_power;
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}
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/*
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* We're trying to get all the cpus to the average_load, so we don't
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* want to push ourselves above the average load, nor do we wish to
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* reduce the max loaded cpu below the average load. At the same time,
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* we also don't want to reduce the group load below the group capacity
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* (so that we can implement power-savings policies etc). Thus we look
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* for the minimum possible imbalance.
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* Be careful of negative numbers as they'll appear as very large values
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* with unsigned longs.
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*/
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max_pull = min(sds->max_load - sds->avg_load, load_above_capacity);
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/* How much load to actually move to equalise the imbalance */
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*imbalance = min(max_pull * sds->busiest->cpu_power,
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@ -2718,7 +2748,6 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
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* 4) This group is more busy than the avg busieness at this
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* sched_domain.
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* 5) The imbalance is within the specified limit.
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* 6) Any rebalance would lead to ping-pong
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*/
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if (!(*balance))
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goto ret;
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@ -2737,25 +2766,6 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
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if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load)
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goto out_balanced;
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sds.busiest_load_per_task /= sds.busiest_nr_running;
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if (sds.group_imb)
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sds.busiest_load_per_task =
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min(sds.busiest_load_per_task, sds.avg_load);
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/*
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* We're trying to get all the cpus to the average_load, so we don't
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* want to push ourselves above the average load, nor do we wish to
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* reduce the max loaded cpu below the average load, as either of these
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* actions would just result in more rebalancing later, and ping-pong
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* tasks around. Thus we look for the minimum possible imbalance.
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* Negative imbalances (*we* are more loaded than anyone else) will
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* be counted as no imbalance for these purposes -- we can't fix that
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* by pulling tasks to us. Be careful of negative numbers as they'll
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* appear as very large values with unsigned longs.
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*/
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if (sds.max_load <= sds.busiest_load_per_task)
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goto out_balanced;
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/* Looks like there is an imbalance. Compute it */
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calculate_imbalance(&sds, this_cpu, imbalance);
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return sds.busiest;
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