1use crate::runtime::{Config, MetricsBatch, WorkerMetrics};
2
3use std::time::{Duration, Instant};
4
5/// Per-worker statistics. This is used for both tuning the scheduler and
6/// reporting runtime-level metrics/stats.
7pub(crate) struct Stats {
8 /// The metrics batch used to report runtime-level metrics/stats to the
9 /// user.
10 batch: MetricsBatch,
11
12 /// Instant at which work last resumed (continued after park).
13 ///
14 /// This duplicates the value stored in `MetricsBatch`. We will unify
15 /// `Stats` and `MetricsBatch` when we stabilize metrics.
16 processing_scheduled_tasks_started_at: Instant,
17
18 /// Number of tasks polled in the batch of scheduled tasks
19 tasks_polled_in_batch: usize,
20
21 /// Exponentially-weighted moving average of time spent polling scheduled a
22 /// task.
23 ///
24 /// Tracked in nanoseconds, stored as a `f64` since that is what we use with
25 /// the EWMA calculations
26 task_poll_time_ewma: f64,
27}
28
29/// How to weigh each individual poll time, value is plucked from thin air.
30const TASK_POLL_TIME_EWMA_ALPHA: f64 = 0.1;
31
32/// Ideally, we wouldn't go above this, value is plucked from thin air.
33const TARGET_GLOBAL_QUEUE_INTERVAL: f64 = Duration::from_micros(200).as_nanos() as f64;
34
35/// Max value for the global queue interval. This is 2x the previous default
36const MAX_TASKS_POLLED_PER_GLOBAL_QUEUE_INTERVAL: u32 = 127;
37
38/// This is the previous default
39const TARGET_TASKS_POLLED_PER_GLOBAL_QUEUE_INTERVAL: u32 = 61;
40
41impl Stats {
42 pub(crate) fn new(worker_metrics: &WorkerMetrics) -> Stats {
43 // Seed the value with what we hope to see.
44 let task_poll_time_ewma =
45 TARGET_GLOBAL_QUEUE_INTERVAL / TARGET_TASKS_POLLED_PER_GLOBAL_QUEUE_INTERVAL as f64;
46
47 Stats {
48 batch: MetricsBatch::new(worker_metrics),
49 processing_scheduled_tasks_started_at: Instant::now(),
50 tasks_polled_in_batch: 0,
51 task_poll_time_ewma,
52 }
53 }
54
55 pub(crate) fn tuned_global_queue_interval(&self, config: &Config) -> u32 {
56 // If an interval is explicitly set, don't tune.
57 if let Some(configured) = config.global_queue_interval {
58 return configured;
59 }
60
61 // As of Rust 1.45, casts from f64 -> u32 are saturating, which is fine here.
62 let tasks_per_interval = (TARGET_GLOBAL_QUEUE_INTERVAL / self.task_poll_time_ewma) as u32;
63
64 // If we are using self-tuning, we don't want to return less than 2 as that would result in the
65 // global queue always getting checked first.
66 tasks_per_interval.clamp(2, MAX_TASKS_POLLED_PER_GLOBAL_QUEUE_INTERVAL)
67 }
68
69 pub(crate) fn submit(&mut self, to: &WorkerMetrics) {
70 self.batch.submit(to, self.task_poll_time_ewma as u64);
71 }
72
73 pub(crate) fn about_to_park(&mut self) {
74 self.batch.about_to_park();
75 }
76
77 pub(crate) fn unparked(&mut self) {
78 self.batch.unparked();
79 }
80
81 pub(crate) fn inc_local_schedule_count(&mut self) {
82 self.batch.inc_local_schedule_count();
83 }
84
85 pub(crate) fn start_processing_scheduled_tasks(&mut self) {
86 self.batch.start_processing_scheduled_tasks();
87
88 self.processing_scheduled_tasks_started_at = Instant::now();
89 self.tasks_polled_in_batch = 0;
90 }
91
92 pub(crate) fn end_processing_scheduled_tasks(&mut self) {
93 self.batch.end_processing_scheduled_tasks();
94
95 // Update the EWMA task poll time
96 if self.tasks_polled_in_batch > 0 {
97 let now = Instant::now();
98
99 // If we "overflow" this conversion, we have bigger problems than
100 // slightly off stats.
101 let elapsed = (now - self.processing_scheduled_tasks_started_at).as_nanos() as f64;
102 let num_polls = self.tasks_polled_in_batch as f64;
103
104 // Calculate the mean poll duration for a single task in the batch
105 let mean_poll_duration = elapsed / num_polls;
106
107 // Compute the alpha weighted by the number of tasks polled this batch.
108 let weighted_alpha = 1.0 - (1.0 - TASK_POLL_TIME_EWMA_ALPHA).powf(num_polls);
109
110 // Now compute the new weighted average task poll time.
111 self.task_poll_time_ewma = weighted_alpha * mean_poll_duration
112 + (1.0 - weighted_alpha) * self.task_poll_time_ewma;
113 }
114 }
115
116 pub(crate) fn start_poll(&mut self) {
117 self.batch.start_poll();
118
119 self.tasks_polled_in_batch += 1;
120 }
121
122 pub(crate) fn end_poll(&mut self) {
123 self.batch.end_poll();
124 }
125
126 pub(crate) fn incr_steal_count(&mut self, by: u16) {
127 self.batch.incr_steal_count(by);
128 }
129
130 pub(crate) fn incr_steal_operations(&mut self) {
131 self.batch.incr_steal_operations();
132 }
133
134 pub(crate) fn incr_overflow_count(&mut self) {
135 self.batch.incr_overflow_count();
136 }
137}
138