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Inline "small" systems into the multithreaded executor #7693

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Inline "small" systems into the multithreaded executor #7693

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130 changes: 102 additions & 28 deletions crates/bevy_ecs/src/schedule/executor/multi_threaded.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
use std::sync::Arc;

use bevy_tasks::{ComputeTaskPool, Scope, TaskPool, ThreadExecutor};
use bevy_utils::default;
use bevy_utils::syncunsafecell::SyncUnsafeCell;
#[cfg(feature = "trace")]
use bevy_utils::tracing::{info_span, Instrument};
use bevy_utils::{default, Duration, Instant};
use std::panic::AssertUnwindSafe;

use async_channel::{Receiver, Sender};
Expand All @@ -23,6 +23,14 @@ use crate::{

use crate as bevy_ecs;

const EXECUTION_TIME_DECAY_RATE: f32 = 0.25;
const INLINE_THRESHOLD: Duration = Duration::from_micros(2);

struct SystemCompletion {
system_index: usize,
duration: Duration,
}

/// A funky borrow split of [`SystemSchedule`] required by the [`MultiThreadedExecutor`].
struct SyncUnsafeSchedule<'a> {
systems: &'a [SyncUnsafeCell<BoxedSystem>],
Expand Down Expand Up @@ -61,14 +69,26 @@ struct SystemTaskMetadata {
is_send: bool,
/// Is `true` if the system is exclusive.
is_exclusive: bool,
/// Weighted average of the execution time of the system.
avg_execution_time: Option<Duration>,
}

impl SystemTaskMetadata {
fn update_exeuction_time(&mut self, mut execution_time: Duration) {
if let Some(avg_execution_time) = self.avg_execution_time {
execution_time = execution_time.mul_f32(EXECUTION_TIME_DECAY_RATE)
+ avg_execution_time.mul_f32(1.0 - EXECUTION_TIME_DECAY_RATE);
}
self.avg_execution_time = Some(execution_time);
}
}

/// Runs the schedule using a thread pool. Non-conflicting systems can run in parallel.
pub struct MultiThreadedExecutor {
/// Sends system completion events.
sender: Sender<usize>,
sender: Sender<SystemCompletion>,
/// Receives system completion events.
receiver: Receiver<usize>,
receiver: Receiver<SystemCompletion>,
/// Metadata for scheduling and running system tasks.
system_task_metadata: Vec<SystemTaskMetadata>,
/// Union of the accesses of all currently running systems.
Expand Down Expand Up @@ -99,6 +119,8 @@ pub struct MultiThreadedExecutor {
unapplied_systems: FixedBitSet,
/// Setting when true applies system buffers after all systems have run
apply_final_buffers: bool,
// A queue of inlined systems that have yet to run.
// inlined_system_queue: Vec<usize>,
}

impl Default for MultiThreadedExecutor {
Expand Down Expand Up @@ -136,6 +158,7 @@ impl SystemExecutor for MultiThreadedExecutor {
dependents: schedule.system_dependents[index].clone(),
is_send: schedule.systems[index].is_send(),
is_exclusive: schedule.systems[index].is_exclusive(),
avg_execution_time: None,
});
}

Expand Down Expand Up @@ -186,15 +209,15 @@ impl SystemExecutor for MultiThreadedExecutor {

if self.num_running_systems > 0 {
// wait for systems to complete
let index =
let completion =
self.receiver.recv().await.expect(
"A system has panicked so the executor cannot continue.",
);

self.finish_system_and_signal_dependents(index);
self.finish_system_and_signal_dependents(completion);

while let Ok(index) = self.receiver.try_recv() {
self.finish_system_and_signal_dependents(index);
while let Ok(completion) = self.receiver.try_recv() {
self.finish_system_and_signal_dependents(completion);
}

self.rebuild_active_access();
Expand Down Expand Up @@ -250,6 +273,7 @@ impl MultiThreadedExecutor {
completed_systems: FixedBitSet::new(),
unapplied_systems: FixedBitSet::new(),
apply_final_buffers: true,
// inlined_system_queue: Vec::new(),
}
}

Expand Down Expand Up @@ -430,6 +454,35 @@ impl MultiThreadedExecutor {
// SAFETY: this system is not running, no other reference exists
let system = unsafe { &mut *systems[system_index].get() };

let &SystemTaskMetadata {
is_send,
avg_execution_time,
..
} = &self.system_task_metadata[system_index];
if let Some(avg_execution_time) = avg_execution_time {
if is_send && avg_execution_time <= INLINE_THRESHOLD {
// #[cfg(feature = "trace")]
// let _system_span = info_span!("system", name = &*system.name()).entered();
let res = std::panic::catch_unwind(AssertUnwindSafe(|| {
let start = Instant::now();
// SAFETY: access is compatible
unsafe { system.run_unsafe((), world) };
Instant::now() - start
}));
if let Ok(duration) = res {
self.finish_system_and_signal_dependents(SystemCompletion {
system_index,
duration,
});
} else {
// close the channel to propagate the error to the
// multithreaded executor
self.sender.close();
}
return;
}
}

#[cfg(feature = "trace")]
let task_span = info_span!("system_task", name = &*system.name());
#[cfg(feature = "trace")]
Expand All @@ -440,20 +493,25 @@ impl MultiThreadedExecutor {
#[cfg(feature = "trace")]
let system_guard = system_span.enter();
let res = std::panic::catch_unwind(AssertUnwindSafe(|| {
let start = Instant::now();
// SAFETY: access is compatible
unsafe { system.run_unsafe((), world) };
Instant::now() - start
}));
#[cfg(feature = "trace")]
drop(system_guard);
if res.is_err() {
// close the channel to propagate the error to the
// multithreaded executor
sender.close();
} else {
if let Ok(duration) = res {
sender
.send(system_index)
.send(SystemCompletion {
system_index,
duration,
})
.await
.unwrap_or_else(|error| unreachable!("{}", error));
} else {
// close the channel to propagate the error to the
// multithreaded executor
sender.close();
}
};

Expand Down Expand Up @@ -498,19 +556,24 @@ impl MultiThreadedExecutor {
#[cfg(feature = "trace")]
let system_guard = system_span.enter();
let res = std::panic::catch_unwind(AssertUnwindSafe(|| {
let start = Instant::now();
apply_system_buffers(&unapplied_systems, systems, world);
Instant::now() - start
}));
#[cfg(feature = "trace")]
drop(system_guard);
if res.is_err() {
// close the channel to propagate the error to the
// multithreaded executor
sender.close();
} else {
if let Ok(duration) = res {
sender
.send(system_index)
.send(SystemCompletion {
system_index,
duration,
})
.await
.unwrap_or_else(|error| unreachable!("{}", error));
} else {
// close the channel to propagate the error to the
// multithreaded executor
sender.close();
}
};

Expand All @@ -522,19 +585,24 @@ impl MultiThreadedExecutor {
#[cfg(feature = "trace")]
let system_guard = system_span.enter();
let res = std::panic::catch_unwind(AssertUnwindSafe(|| {
let start = Instant::now();
system.run((), world);
Instant::now() - start
}));
#[cfg(feature = "trace")]
drop(system_guard);
if res.is_err() {
// close the channel to propagate the error to the
// multithreaded executor
sender.close();
} else {
if let Ok(duration) = res {
sender
.send(system_index)
.send(SystemCompletion {
system_index,
duration,
})
.await
.unwrap_or_else(|error| unreachable!("{}", error));
} else {
// close the channel to propagate the error to the
// multithreaded executor
sender.close();
}
};

Expand All @@ -547,12 +615,18 @@ impl MultiThreadedExecutor {
self.local_thread_running = true;
}

fn finish_system_and_signal_dependents(&mut self, system_index: usize) {
if self.system_task_metadata[system_index].is_exclusive {
fn finish_system_and_signal_dependents(&mut self, completion: SystemCompletion) {
let SystemCompletion {
system_index,
duration,
} = completion;
let metadata = &mut self.system_task_metadata[system_index];
metadata.update_exeuction_time(duration);
if metadata.is_exclusive {
self.exclusive_running = false;
}

if !self.system_task_metadata[system_index].is_send {
if !metadata.is_send {
self.local_thread_running = false;
}

Expand Down