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Cache parallel iteration spans (#9950)
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# Objective
We cached system spans in #9390, but another common span seen in most
Bevy apps when enabling tracing are Query::par_iter(_mut) related spans.

## Solution
Cache them in QueryState. The one downside to this is that we pay for
the memory for every Query(State) instantiated, not just those that are
used for parallel iteration, but this shouldn't be a significant cost
unless the app is creating hundreds of thousands of Query(State)s
regularly.

## Metrics
Tested against `cargo run --profile stress-test --features trace_tracy
--example many_cubes`. Yellow is this PR, red is main.

`sync_simple_transforms`:


![image](https://github.com/bevyengine/bevy/assets/3137680/d60f6d69-5586-4424-9d78-aac78992aacd)

`check_visibility`:


![image](https://github.com/bevyengine/bevy/assets/3137680/096a58d2-a330-4a32-b806-09cd524e6e15)

Full frame:


![image](https://github.com/bevyengine/bevy/assets/3137680/3b088cf8-9487-4bc7-a308-026e172d6672)
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james7132 authored Sep 30, 2023
1 parent 857fb9c commit 95813b8
Showing 1 changed file with 18 additions and 27 deletions.
45 changes: 18 additions & 27 deletions crates/bevy_ecs/src/query/state.rs
Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use crate::{
world::{unsafe_world_cell::UnsafeWorldCell, World, WorldId},
};
#[cfg(feature = "trace")]
use bevy_utils::tracing::Instrument;
use bevy_utils::tracing::Span;
use fixedbitset::FixedBitSet;
use std::{any::TypeId, borrow::Borrow, fmt, mem::MaybeUninit};

Expand All @@ -39,6 +39,8 @@ pub struct QueryState<Q: WorldQuery, F: ReadOnlyWorldQuery = ()> {
pub(crate) matched_archetype_ids: Vec<ArchetypeId>,
pub(crate) fetch_state: Q::State,
pub(crate) filter_state: F::State,
#[cfg(feature = "trace")]
par_iter_span: Span,
}

impl<Q: WorldQuery, F: ReadOnlyWorldQuery> std::fmt::Debug for QueryState<Q, F> {
Expand Down Expand Up @@ -125,6 +127,12 @@ impl<Q: WorldQuery, F: ReadOnlyWorldQuery> QueryState<Q, F> {
matched_tables: Default::default(),
matched_archetypes: Default::default(),
archetype_component_access: Default::default(),
#[cfg(feature = "trace")]
par_iter_span: bevy_utils::tracing::info_span!(
"par_for_each",
query = std::any::type_name::<Q>(),
filter = std::any::type_name::<F>(),
),
};
state.update_archetypes(world);
state
Expand Down Expand Up @@ -1205,7 +1213,9 @@ impl<Q: WorldQuery, F: ReadOnlyWorldQuery> QueryState<Q, F> {
while offset < table.entity_count() {
let func = func.clone();
let len = batch_size.min(table.entity_count() - offset);
let task = async move {
scope.spawn(async move {
#[cfg(feature = "trace")]
let _span = self.par_iter_span.enter();
let mut fetch =
Q::init_fetch(world, &self.fetch_state, last_run, this_run);
let mut filter =
Expand All @@ -1223,17 +1233,7 @@ impl<Q: WorldQuery, F: ReadOnlyWorldQuery> QueryState<Q, F> {
}
func(Q::fetch(&mut fetch, *entity, row));
}
};
#[cfg(feature = "trace")]
let span = bevy_utils::tracing::info_span!(
"par_for_each",
query = std::any::type_name::<Q>(),
filter = std::any::type_name::<F>(),
count = len,
);
#[cfg(feature = "trace")]
let task = task.instrument(span);
scope.spawn(task);
});
offset += batch_size;
}
}
Expand All @@ -1249,7 +1249,9 @@ impl<Q: WorldQuery, F: ReadOnlyWorldQuery> QueryState<Q, F> {
while offset < archetype.len() {
let func = func.clone();
let len = batch_size.min(archetype.len() - offset);
let task = async move {
scope.spawn(async move {
#[cfg(feature = "trace")]
let _span = self.par_iter_span.enter();
let mut fetch =
Q::init_fetch(world, &self.fetch_state, last_run, this_run);
let mut filter =
Expand Down Expand Up @@ -1277,19 +1279,8 @@ impl<Q: WorldQuery, F: ReadOnlyWorldQuery> QueryState<Q, F> {
archetype_entity.table_row(),
));
}
};

#[cfg(feature = "trace")]
let span = bevy_utils::tracing::info_span!(
"par_for_each",
query = std::any::type_name::<Q>(),
filter = std::any::type_name::<F>(),
count = len,
);
#[cfg(feature = "trace")]
let task = task.instrument(span);

scope.spawn(task);
});

offset += batch_size;
}
}
Expand Down

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