Messages in this thread Patch in this message |  | | From | Morten Rasmussen <> | Subject | [PATCH v5 5/6] sched/fair: Track peak per-entity utilization | Date | Fri, 14 Oct 2016 14:41:11 +0100 |
| |
When using PELT (per-entity load tracking) utilization to place tasks at wake-up using the decayed utilization (due to sleep) leads to under-estimation of true utilization of the task. This could mean putting the task on a cpu with less available capacity than is actually needed. This issue can be mitigated by using 'peak' utilization instead of the decayed utilization for placement decisions, e.g. at task wake-up.
The 'peak' utilization metric, util_peak, tracks util_avg when the task is running and retains its previous value while the task is blocked/waiting on the rq. It is instantly updated to track util_avg again as soon as the task running again.
cc: Ingo Molnar <mingo@redhat.com> cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- include/linux/sched.h | 2 +- kernel/sched/fair.c | 23 +++++++++++++++++------ 2 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index ad51978ff15e..988d7f48604e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1294,7 +1294,7 @@ struct load_weight { struct sched_avg { u64 last_update_time, load_sum; u32 util_sum, period_contrib; - unsigned long load_avg, util_avg; + unsigned long load_avg, util_avg, util_peak; }; #ifdef CONFIG_SCHEDSTATS diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a5efafda23ef..e0abff77764f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -696,6 +696,7 @@ void init_entity_runnable_average(struct sched_entity *se) * At this point, util_avg won't be used in select_task_rq_fair anyway */ sa->util_avg = 0; + sa->util_peak = 0; sa->util_sum = 0; /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */ } @@ -747,6 +748,7 @@ void post_init_entity_util_avg(struct sched_entity *se) } else { sa->util_avg = cap; } + sa->util_peak = sa->util_avg; sa->util_sum = sa->util_avg * LOAD_AVG_MAX; } @@ -3515,6 +3517,10 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) */ if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE) update_min_vruntime(cfs_rq); + + /* Save peak PELT utilization for task to help wake-up decisions */ + if (flags & DEQUEUE_SLEEP && entity_is_task(se)) + se->avg.util_peak = se->avg.util_avg; } /* @@ -5203,7 +5209,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, return 1; } -static inline int task_util(struct task_struct *p); +static inline int task_util_peak(struct task_struct *p); static int cpu_util_wake(int cpu, struct task_struct *p); static unsigned long capacity_spare_wake(int cpu, struct task_struct *p) @@ -5286,14 +5292,14 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, /* * The cross-over point between using spare capacity or least load * is too conservative for high utilization tasks on partially - * utilized systems if we require spare_capacity > task_util(p), + * utilized systems if we require spare_capacity > task_util_peak(p), * so we allow for some task stuffing by using - * spare_capacity > task_util(p)/2. + * spare_capacity > task_util_peak(p)/2. */ - if (this_spare > task_util(p) / 2 && + if (this_spare > task_util_peak(p) / 2 && imbalance*this_spare > 100*most_spare) return NULL; - else if (most_spare > task_util(p) / 2) + else if (most_spare > task_util_peak(p) / 2) return most_spare_sg; if (!idlest || 100*this_load < imbalance*min_load) @@ -5628,6 +5634,11 @@ static inline int task_util(struct task_struct *p) return p->se.avg.util_avg; } +static inline int task_util_peak(struct task_struct *p) +{ + return p->se.avg.util_peak; +} + /* * cpu_util_wake: Compute cpu utilization with any contributions from * the waking task p removed. @@ -5667,7 +5678,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) /* Bring task utilization in sync with prev_cpu */ sync_entity_load_avg(&p->se); - return min_cap * 1024 < task_util(p) * capacity_margin; + return min_cap * 1024 < task_util_peak(p) * capacity_margin; } /* -- 2.7.4
|  |