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rt(threaded): basic self-tuning of injection queue #5720

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Jun 1, 2023
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65 changes: 59 additions & 6 deletions benches/rt_multi_threaded.rs
Original file line number Diff line number Diff line change
Expand Up @@ -6,12 +6,14 @@ use tokio::runtime::{self, Runtime};
use tokio::sync::oneshot;

use bencher::{benchmark_group, benchmark_main, Bencher};
use std::sync::atomic::AtomicUsize;
use std::sync::atomic::Ordering::Relaxed;
use std::sync::atomic::{AtomicBool, AtomicUsize};
use std::sync::{mpsc, Arc};
use std::time::{Duration, Instant};

const NUM_WORKERS: usize = 4;
const NUM_SPAWN: usize = 10_000;
const STALL_DUR: Duration = Duration::from_micros(10);

fn spawn_many_local(b: &mut Bencher) {
let rt = rt();
Expand Down Expand Up @@ -57,19 +59,60 @@ fn spawn_many_remote_idle(b: &mut Bencher) {
});
}

fn spawn_many_remote_busy(b: &mut Bencher) {
fn spawn_many_remote_busy1(b: &mut Bencher) {
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let rt = rt();
let rt_handle = rt.handle();
let mut handles = Vec::with_capacity(NUM_SPAWN);
let flag = Arc::new(AtomicBool::new(true));

// Spawn some tasks to keep the runtimes busy
for _ in 0..(2 * NUM_WORKERS) {
rt.spawn(async {
loop {
let flag = flag.clone();
rt.spawn(async move {
while flag.load(Relaxed) {
tokio::task::yield_now().await;
std::thread::sleep(std::time::Duration::from_micros(10));
stall();
}
});
}

b.iter(|| {
for _ in 0..NUM_SPAWN {
handles.push(rt_handle.spawn(async {}));
}

rt.block_on(async {
for handle in handles.drain(..) {
handle.await.unwrap();
}
});
});

flag.store(false, Relaxed);
}

fn spawn_many_remote_busy2(b: &mut Bencher) {
const NUM_SPAWN: usize = 1_000;

let rt = rt();
let rt_handle = rt.handle();
let mut handles = Vec::with_capacity(NUM_SPAWN);
let flag = Arc::new(AtomicBool::new(true));

// Spawn some tasks to keep the runtimes busy
for _ in 0..(NUM_WORKERS) {
let flag = flag.clone();
fn iter(flag: Arc<AtomicBool>) {
tokio::spawn(async {
if flag.load(Relaxed) {
stall();
iter(flag);
}
});
}
rt.spawn(async {
iter(flag);
});
}

b.iter(|| {
Expand All @@ -83,6 +126,8 @@ fn spawn_many_remote_busy(b: &mut Bencher) {
}
});
});

flag.store(false, Relaxed);
}

fn yield_many(b: &mut Bencher) {
Expand Down Expand Up @@ -193,11 +238,19 @@ fn rt() -> Runtime {
.unwrap()
}

fn stall() {
let now = Instant::now();
while now.elapsed() < STALL_DUR {
std::thread::yield_now();
}
}

benchmark_group!(
scheduler,
spawn_many_local,
spawn_many_remote_idle,
spawn_many_remote_busy,
spawn_many_remote_busy1,
spawn_many_remote_busy2,
ping_pong,
yield_many,
chained_spawn,
Expand Down
12 changes: 6 additions & 6 deletions tokio/src/runtime/builder.rs
Original file line number Diff line number Diff line change
Expand Up @@ -82,7 +82,7 @@ pub struct Builder {
pub(super) keep_alive: Option<Duration>,

/// How many ticks before pulling a task from the global/remote queue?
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pub(super) global_queue_interval: u32,
pub(super) global_queue_interval: Option<u32>,

/// How many ticks before yielding to the driver for timer and I/O events?
pub(super) event_interval: u32,
Expand Down Expand Up @@ -211,7 +211,7 @@ impl Builder {
#[cfg(not(loom))]
const EVENT_INTERVAL: u32 = 61;

Builder::new(Kind::CurrentThread, 31, EVENT_INTERVAL)
Builder::new(Kind::CurrentThread, EVENT_INTERVAL)
}

cfg_not_wasi! {
Expand All @@ -222,15 +222,15 @@ impl Builder {
#[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
pub fn new_multi_thread() -> Builder {
// The number `61` is fairly arbitrary. I believe this value was copied from golang.
Builder::new(Kind::MultiThread, 61, 61)
Builder::new(Kind::MultiThread, 61)
}
}

/// Returns a new runtime builder initialized with default configuration
/// values.
///
/// Configuration methods can be chained on the return value.
pub(crate) fn new(kind: Kind, global_queue_interval: u32, event_interval: u32) -> Builder {
pub(crate) fn new(kind: Kind, event_interval: u32) -> Builder {
Builder {
kind,

Expand Down Expand Up @@ -266,7 +266,7 @@ impl Builder {

// Defaults for these values depend on the scheduler kind, so we get them
// as parameters.
global_queue_interval,
global_queue_interval: None,
event_interval,

seed_generator: RngSeedGenerator::new(RngSeed::new()),
Expand Down Expand Up @@ -716,7 +716,7 @@ impl Builder {
/// # }
/// ```
pub fn global_queue_interval(&mut self, val: u32) -> &mut Self {
self.global_queue_interval = val;
self.global_queue_interval = Some(val);
self
}

Expand Down
2 changes: 1 addition & 1 deletion tokio/src/runtime/config.rs
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use crate::util::RngSeedGenerator;

pub(crate) struct Config {
/// How many ticks before pulling a task from the global/remote queue?
pub(crate) global_queue_interval: u32,
pub(crate) global_queue_interval: Option<u32>,

/// How many ticks before yielding to the driver for timer and I/O events?
pub(crate) event_interval: u32,
Expand Down
20 changes: 13 additions & 7 deletions tokio/src/runtime/metrics/batch.rs
Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,7 @@ pub(crate) struct MetricsBatch {
busy_duration_total: u64,

/// Instant at which work last resumed (continued after park).
last_resume_time: Instant,
processing_scheduled_tasks_started_at: Instant,

/// If `Some`, tracks poll times in nanoseconds
poll_timer: Option<PollTimer>,
Expand Down Expand Up @@ -62,7 +62,7 @@ impl MetricsBatch {
local_schedule_count: 0,
overflow_count: 0,
busy_duration_total: 0,
last_resume_time: now,
processing_scheduled_tasks_started_at: now,
poll_timer: worker_metrics
.poll_count_histogram
.as_ref()
Expand Down Expand Up @@ -106,11 +106,20 @@ impl MetricsBatch {
} else {
self.poll_count_on_last_park = self.poll_count;
}
}

/// Start processing a batch of tasks
pub(crate) fn start_processing_scheduled_tasks(&mut self) {
self.processing_scheduled_tasks_started_at = Instant::now();
}

let busy_duration = self.last_resume_time.elapsed();
/// Stop processing a batch of tasks
pub(crate) fn end_processing_scheduled_tasks(&mut self) {
let busy_duration = self.processing_scheduled_tasks_started_at.elapsed();
self.busy_duration_total += duration_as_u64(busy_duration);
}

/// Start polling an individual task
pub(crate) fn start_poll(&mut self) {
self.poll_count += 1;

Expand All @@ -119,17 +128,14 @@ impl MetricsBatch {
}
}

/// Stop polling an individual task
pub(crate) fn end_poll(&mut self) {
if let Some(poll_timer) = &mut self.poll_timer {
let elapsed = duration_as_u64(poll_timer.poll_started_at.elapsed());
poll_timer.poll_counts.measure(elapsed, 1);
}
}

pub(crate) fn returned_from_park(&mut self) {
self.last_resume_time = Instant::now();
}

pub(crate) fn inc_local_schedule_count(&mut self) {
self.local_schedule_count += 1;
}
Expand Down
3 changes: 2 additions & 1 deletion tokio/src/runtime/metrics/mock.rs
Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,9 @@ impl MetricsBatch {

pub(crate) fn submit(&mut self, _to: &WorkerMetrics) {}
pub(crate) fn about_to_park(&mut self) {}
pub(crate) fn returned_from_park(&mut self) {}
pub(crate) fn inc_local_schedule_count(&mut self) {}
pub(crate) fn start_processing_scheduled_tasks(&mut self) {}
pub(crate) fn end_processing_scheduled_tasks(&mut self) {}
pub(crate) fn start_poll(&mut self) {}
pub(crate) fn end_poll(&mut self) {}
}
Expand Down
27 changes: 25 additions & 2 deletions tokio/src/runtime/scheduler/current_thread.rs
Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,9 @@ struct Core {
/// Metrics batch
metrics: MetricsBatch,

/// How often to check the global queue
global_queue_interval: u32,

/// True if a task panicked without being handled and the runtime is
/// configured to shutdown on unhandled panic.
unhandled_panic: bool,
Expand Down Expand Up @@ -100,6 +103,11 @@ type Notified = task::Notified<Arc<Handle>>;
/// Initial queue capacity.
const INITIAL_CAPACITY: usize = 64;

/// Used if none is specified. This is a temporary constant and will be removed
/// as we unify tuning logic between the multi-thread and current-thread
/// schedulers.
const DEFAULT_GLOBAL_QUEUE_INTERVAL: u32 = 61;

// Tracks the current CurrentThread.
scoped_thread_local!(static CURRENT: Context);

Expand All @@ -113,6 +121,11 @@ impl CurrentThread {
) -> (CurrentThread, Arc<Handle>) {
let worker_metrics = WorkerMetrics::from_config(&config);

// Get the configured global queue interval, or use the default.
let global_queue_interval = config
.global_queue_interval
.unwrap_or(DEFAULT_GLOBAL_QUEUE_INTERVAL);

let handle = Arc::new(Handle {
shared: Shared {
inject: Inject::new(),
Expand All @@ -132,6 +145,7 @@ impl CurrentThread {
tick: 0,
driver: Some(driver),
metrics: MetricsBatch::new(&handle.shared.worker_metrics),
global_queue_interval,
unhandled_panic: false,
})));

Expand Down Expand Up @@ -255,7 +269,7 @@ impl Core {
}

fn next_task(&mut self, handle: &Handle) -> Option<Notified> {
if self.tick % handle.shared.config.global_queue_interval == 0 {
if self.tick % self.global_queue_interval == 0 {
handle
.next_remote_task()
.or_else(|| self.next_local_task(handle))
Expand Down Expand Up @@ -344,7 +358,6 @@ impl Context {
});

core = c;
core.metrics.returned_from_park();
}

if let Some(f) = &handle.shared.config.after_unpark {
Expand Down Expand Up @@ -603,6 +616,8 @@ impl CoreGuard<'_> {

pin!(future);

core.metrics.start_processing_scheduled_tasks();

'outer: loop {
let handle = &context.handle;

Expand Down Expand Up @@ -631,12 +646,16 @@ impl CoreGuard<'_> {
let task = match entry {
Some(entry) => entry,
None => {
core.metrics.end_processing_scheduled_tasks();

core = if did_defer_tasks() {
context.park_yield(core, handle)
} else {
context.park(core, handle)
};

core.metrics.start_processing_scheduled_tasks();

// Try polling the `block_on` future next
continue 'outer;
}
Expand All @@ -651,9 +670,13 @@ impl CoreGuard<'_> {
core = c;
}

core.metrics.end_processing_scheduled_tasks();

// Yield to the driver, this drives the timer and pulls any
// pending I/O events.
core = context.park_yield(core, handle);

core.metrics.start_processing_scheduled_tasks();
}
});

Expand Down
3 changes: 3 additions & 0 deletions tokio/src/runtime/scheduler/multi_thread/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,9 @@ pub(crate) use handle::Handle;
mod idle;
use self::idle::Idle;

mod stats;
pub(crate) use stats::Stats;

mod park;
pub(crate) use park::{Parker, Unparker};

Expand Down
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