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authorYuyang Du <yuyang.du@intel.com>2015-07-15 08:04:37 +0800
committerIngo Molnar <mingo@kernel.org>2015-08-03 12:21:29 +0200
commit9d89c257dfb9c51a532d69397f6eed75e5168c35 (patch)
tree6271fea81648a9212e0567d886d9d79b84b17621 /kernel/sched/debug.c
parentcd126afe838d7ea9b971cdea087fd498a7293c7f (diff)
sched/fair: Rewrite runnable load and utilization average tracking
The idea of runnable load average (let runnable time contribute to weight) was proposed by Paul Turner and Ben Segall, and it is still followed by this rewrite. This rewrite aims to solve the following issues: 1. cfs_rq's load average (namely runnable_load_avg and blocked_load_avg) is updated at the granularity of an entity at a time, which results in the cfs_rq's load average is stale or partially updated: at any time, only one entity is up to date, all other entities are effectively lagging behind. This is undesirable. To illustrate, if we have n runnable entities in the cfs_rq, as time elapses, they certainly become outdated: t0: cfs_rq { e1_old, e2_old, ..., en_old } and when we update: t1: update e1, then we have cfs_rq { e1_new, e2_old, ..., en_old } t2: update e2, then we have cfs_rq { e1_old, e2_new, ..., en_old } ... We solve this by combining all runnable entities' load averages together in cfs_rq's avg, and update the cfs_rq's avg as a whole. This is based on the fact that if we regard the update as a function, then: w * update(e) = update(w * e) and update(e1) + update(e2) = update(e1 + e2), then w1 * update(e1) + w2 * update(e2) = update(w1 * e1 + w2 * e2) therefore, by this rewrite, we have an entirely updated cfs_rq at the time we update it: t1: update cfs_rq { e1_new, e2_new, ..., en_new } t2: update cfs_rq { e1_new, e2_new, ..., en_new } ... 2. cfs_rq's load average is different between top rq->cfs_rq and other task_group's per CPU cfs_rqs in whether or not blocked_load_average contributes to the load. The basic idea behind runnable load average (the same for utilization) is that the blocked state is taken into account as opposed to only accounting for the currently runnable state. Therefore, the average should include both the runnable/running and blocked load averages. This rewrite does that. In addition, we also combine runnable/running and blocked averages of all entities into the cfs_rq's average, and update it together at once. This is based on the fact that: update(runnable) + update(blocked) = update(runnable + blocked) This significantly reduces the code as we don't need to separately maintain/update runnable/running load and blocked load. 3. How task_group entities' share is calculated is complex and imprecise. We reduce the complexity in this rewrite to allow a very simple rule: the task_group's load_avg is aggregated from its per CPU cfs_rqs's load_avgs. Then group entity's weight is simply proportional to its own cfs_rq's load_avg / task_group's load_avg. To illustrate, if a task_group has { cfs_rq1, cfs_rq2, ..., cfs_rqn }, then, task_group_avg = cfs_rq1_avg + cfs_rq2_avg + ... + cfs_rqn_avg, then cfs_rqx's entity's share = cfs_rqx_avg / task_group_avg * task_group's share To sum up, this rewrite in principle is equivalent to the current one, but fixes the issues described above. Turns out, it significantly reduces the code complexity and hence increases clarity and efficiency. In addition, the new averages are more smooth/continuous (no spurious spikes and valleys) and updated more consistently and quickly to reflect the load dynamics. As a result, we have less load tracking overhead, better performance, and especially better power efficiency due to more balanced load. Signed-off-by: Yuyang Du <yuyang.du@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: arjan@linux.intel.com Cc: bsegall@google.com Cc: dietmar.eggemann@arm.com Cc: fengguang.wu@intel.com Cc: len.brown@intel.com Cc: morten.rasmussen@arm.com Cc: pjt@google.com Cc: rafael.j.wysocki@intel.com Cc: umgwanakikbuti@gmail.com Cc: vincent.guittot@linaro.org Link: http://lkml.kernel.org/r/1436918682-4971-3-git-send-email-yuyang.du@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/debug.c')
-rw-r--r--kernel/sched/debug.c41
1 files changed, 17 insertions, 24 deletions
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 363b7e82554b..74f276f5568c 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -88,12 +88,8 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
#endif
P(se->load.weight);
#ifdef CONFIG_SMP
- P(se->avg.runnable_avg_sum);
- P(se->avg.running_avg_sum);
- P(se->avg.avg_period);
- P(se->avg.load_avg_contrib);
- P(se->avg.utilization_avg_contrib);
- P(se->avg.decay_count);
+ P(se->avg.load_avg);
+ P(se->avg.util_avg);
#endif
#undef PN
#undef P
@@ -209,21 +205,19 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
SEQ_printf(m, " .%-30s: %d\n", "nr_running", cfs_rq->nr_running);
SEQ_printf(m, " .%-30s: %ld\n", "load", cfs_rq->load.weight);
#ifdef CONFIG_SMP
- SEQ_printf(m, " .%-30s: %ld\n", "runnable_load_avg",
- cfs_rq->runnable_load_avg);
- SEQ_printf(m, " .%-30s: %ld\n", "blocked_load_avg",
- cfs_rq->blocked_load_avg);
- SEQ_printf(m, " .%-30s: %ld\n", "utilization_load_avg",
- cfs_rq->utilization_load_avg);
+ SEQ_printf(m, " .%-30s: %lu\n", "load_avg",
+ cfs_rq->avg.load_avg);
+ SEQ_printf(m, " .%-30s: %lu\n", "util_avg",
+ cfs_rq->avg.util_avg);
+ SEQ_printf(m, " .%-30s: %ld\n", "removed_load_avg",
+ atomic_long_read(&cfs_rq->removed_load_avg));
+ SEQ_printf(m, " .%-30s: %ld\n", "removed_util_avg",
+ atomic_long_read(&cfs_rq->removed_util_avg));
#ifdef CONFIG_FAIR_GROUP_SCHED
- SEQ_printf(m, " .%-30s: %ld\n", "tg_load_contrib",
- cfs_rq->tg_load_contrib);
- SEQ_printf(m, " .%-30s: %d\n", "tg_runnable_contrib",
- cfs_rq->tg_runnable_contrib);
+ SEQ_printf(m, " .%-30s: %lu\n", "tg_load_avg_contrib",
+ cfs_rq->tg_load_avg_contrib);
SEQ_printf(m, " .%-30s: %ld\n", "tg_load_avg",
atomic_long_read(&cfs_rq->tg->load_avg));
- SEQ_printf(m, " .%-30s: %d\n", "tg->runnable_avg",
- atomic_read(&cfs_rq->tg->runnable_avg));
#endif
#endif
#ifdef CONFIG_CFS_BANDWIDTH
@@ -631,12 +625,11 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
P(se.load.weight);
#ifdef CONFIG_SMP
- P(se.avg.runnable_avg_sum);
- P(se.avg.running_avg_sum);
- P(se.avg.avg_period);
- P(se.avg.load_avg_contrib);
- P(se.avg.utilization_avg_contrib);
- P(se.avg.decay_count);
+ P(se.avg.load_sum);
+ P(se.avg.util_sum);
+ P(se.avg.load_avg);
+ P(se.avg.util_avg);
+ P(se.avg.last_update_time);
#endif
P(policy);
P(prio);