`TaskDeps` improvements #147508

nnethercote · 2025-10-09T05:19:58Z

Some cleanups and minor perf improvements relating to TaskDeps.

There are only two places that create a `TaskDeps`. One constructs it manually, the other uses `default`. It's weird that `default()` uses a capacity of 128. This commit just gets rid of `default` and introduces `new` so that both construction sites can be equivalent.

`INLINE_CAPACITY` has two different uses: - It dictates the inline capacity of `EdgesVec::edges`, which is a `SmallVec`. - It dictates when `TaskDeps` switches from a linear scan lookup to a hashset lookup to determine if an edge has been seen before. These two uses are in the same part of the code, but they're fundamentally separate and don't need to use the same constant. This commit separates the two uses, and adds some helpful comments, making the code clearer. It also changes the value used for the linear/hashset threshold from 8 to 16, which gives slightly better perf.

nnethercote · 2025-10-09T05:20:26Z

@bors try @rust-timer queue

`TaskDeps` improvements

rust-bors · 2025-10-09T11:22:41Z

💥 Test timed out after 21600s

nnethercote · 2025-10-09T20:34:07Z

@bors retry

nnethercote · 2025-10-09T22:03:20Z

@bors try @rust-timer queue

`TaskDeps` improvements

rust-bors · 2025-10-10T00:15:08Z

☀️ Try build successful (CI)
Build commit: e4658cf (e4658cffaf309c44def5c182c71fc3b1e4f810d8, parent: b925a865e2c9a0aefe5a2877863cb4df796f2eaf)

rust-timer · 2025-10-10T03:07:10Z

Finished benchmarking commit (e4658cf): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.6%, 0.8%]	3
Regressions ❌ (secondary)	0.8%	[0.2%, 1.0%]	22
Improvements ✅ (primary)	-0.4%	[-1.2%, -0.1%]	29
Improvements ✅ (secondary)	-0.5%	[-1.1%, -0.1%]	23
All ❌✅ (primary)	-0.3%	[-1.2%, 0.8%]	32

Max RSS (memory usage)

Results (primary -0.8%, secondary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.9%	[0.8%, 2.5%]	3
Regressions ❌ (secondary)	1.8%	[1.2%, 2.3%]	2
Improvements ✅ (primary)	-4.8%	[-8.8%, -0.9%]	2
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.0%]	2
All ❌✅ (primary)	-0.8%	[-8.8%, 2.5%]	5

Cycles

Results (secondary -1.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.2%	[2.0%, 4.3%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-4.0%, -2.2%]	7
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 472.277s -> 472.516s (0.05%)
Artifact size: 388.06 MiB -> 388.09 MiB (0.01%)

bors · 2025-10-15T09:50:46Z

⌛ Testing commit 5d00076 with merge 89342a8...

`TaskDeps` improvements Some cleanups and minor perf improvements relating to `TaskDeps`. r? `@saethlin`

bors · 2025-10-15T10:03:40Z

💔 Test failed - checks-actions

nnethercote · 2025-10-15T10:17:14Z

Uh, what?

@bors retry

rust-log-analyzer · 2025-10-15T11:17:25Z

A job failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

##[endgroup]
Image input checksum da75e33fbcc6bcc3f436fedc7bbe55684a3f7a37b83ffcbfc5c587652c6f86a6ee2d93cf356e1bd2824f4f3cdacdaf47e2a47b47f7619a9190ab588ebcc118e3
##[group]Building docker image for x86_64-rust-for-linux
Docker version 28.0.4, build b8034c0
Error response from daemon: Get "https://ghcr.io/v2/": Get "https://ghcr.io/token?account=rust-lang&client_id=docker&offline_token=true&service=ghcr.io": net/http: request canceled (Client.Timeout exceeded while awaiting headers) (Client.Timeout exceeded while awaiting headers)
****************************************************************************
To find more information about this job, visit the following URL:
https://rustc-dev-guide.rust-lang.org/tests/rust-for-linux.html
****************************************************************************
##[error]Process completed with exit code 1.

nnethercote · 2025-10-15T20:31:14Z

@bors retry

`TaskDeps` improvements Some cleanups and minor perf improvements relating to `TaskDeps`. r? `@saethlin`

bors · 2025-10-16T11:40:04Z

⌛ Testing commit 5d00076 with merge 3b3b2ea...

rust-log-analyzer · 2025-10-16T14:03:56Z

The job x86_64-mingw-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)


error: test failed, to rerun pass `-p std --test sync`
Bootstrap failed while executing `test --stage 2 --skip=compiler --skip=src`
Build completed unsuccessfully in 2:14:36
make: *** [Makefile:123: ci-mingw-x] Error 1
  local time: Thu Oct 16 14:03:24 CUT 2025
  network time: Thu, 16 Oct 2025 14:03:25 GMT
##[error]Process completed with exit code 2.
##[group]Run echo "disk usage:"
echo "disk usage:"

bors · 2025-10-16T14:04:18Z

💔 Test failed - checks-actions

nnethercote · 2025-10-16T20:05:14Z

The real failure was this, which doesn't seem related to the changes in this PR, sigh:

2025-10-16T14:03:24.5908828Z failures:
2025-10-16T14:03:24.5909052Z 
2025-10-16T14:03:24.5909735Z ---- condvar::nonpoison_timeout_nanoseconds stdout ----
2025-10-16T14:03:24.5910121Z 
2025-10-16T14:03:24.5910856Z thread 'condvar::nonpoison_timeout_nanoseconds' (3328) panicked at library\std\tests\sync\condvar.rs:298:13:
2025-10-16T14:03:24.5912086Z assertion failed: *guard
2025-10-16T14:03:24.5912443Z stack backtrace:
2025-10-16T14:03:24.5912756Z    0: __rustc::rust_begin_unwind
2025-10-16T14:03:24.5913140Z    1: core::panicking::panic_fmt
2025-10-16T14:03:24.5913533Z    2: core::panicking::panic
2025-10-16T14:03:24.5913941Z    3: core::ops::function::FnOnce::call_once
2025-10-16T14:03:24.5914587Z note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
2025-10-16T14:03:24.5915323Z ---- condvar::nonpoison_timeout_nanoseconds stdout end ----
2025-10-16T14:03:24.5915726Z 
2025-10-16T14:03:24.5915831Z failures:
2025-10-16T14:03:24.5916130Z     condvar::nonpoison_timeout_nanoseconds
2025-10-16T14:03:24.5916431Z 
2025-10-16T14:03:24.5916831Z test result: FAILED. 316 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 3.36s

saethlin · 2025-10-16T21:44:29Z

Agreed. I'm really starting to wonder if this PR is cursed.

nnethercote · 2025-10-17T01:55:45Z

@bors retry

bors · 2025-10-17T04:47:47Z

⌛ Testing commit 5d00076 with merge 28c4c7d...

bors · 2025-10-17T07:56:14Z

☀️ Test successful - checks-actions
Approved by: saethlin
Pushing 28c4c7d to master...

github-actions · 2025-10-17T07:59:39Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 53a741f (parent) -> 28c4c7d (this PR)

Test differences

No test diffs found

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 28c4c7d7abced7b35c49f38149b9cb6ea27dd2a6 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-x86_64-apple: 10030.7s -> 6584.0s (-34.4%)
dist-aarch64-apple: 9278.1s -> 6414.9s (-30.9%)
dist-apple-various: 4705.3s -> 3663.8s (-22.1%)
dist-aarch64-msvc: 5644.3s -> 6829.8s (21.0%)
aarch64-apple: 9168.3s -> 7696.0s (-16.1%)
x86_64-gnu-llvm-20-1: 3681.7s -> 3188.3s (-13.4%)
x86_64-gnu-tools: 3318.6s -> 3661.0s (10.3%)
test-various: 4908.3s -> 4408.2s (-10.2%)
dist-powerpc-linux: 5504.2s -> 4961.2s (-9.9%)
x86_64-msvc-ext3: 7021.4s -> 6361.3s (-9.4%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-10-17T09:07:09Z

Finished benchmarking commit (28c4c7d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	0.5%	[0.2%, 0.8%]	17
Improvements ✅ (primary)	-0.4%	[-1.0%, -0.1%]	25
Improvements ✅ (secondary)	-0.7%	[-1.2%, -0.2%]	22
All ❌✅ (primary)	-0.4%	[-1.0%, 0.5%]	26

Max RSS (memory usage)

Results (primary 0.8%, secondary -1.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	1.8%	[1.8%, 1.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.1%	[-4.1%, -2.1%]	2
All ❌✅ (primary)	0.8%	[0.8%, 0.8%]	1

Cycles

Results (primary -3.9%, secondary 1.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	6.1%	[6.1%, 6.1%]	1
Improvements ✅ (primary)	-3.9%	[-3.9%, -3.9%]	1
Improvements ✅ (secondary)	-3.4%	[-3.4%, -3.4%]	1
All ❌✅ (primary)	-3.9%	[-3.9%, -3.9%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 475.105s -> 474.3s (-0.17%)
Artifact size: 390.35 MiB -> 390.30 MiB (-0.01%)

nnethercote added 4 commits October 9, 2025 11:18

Use contains with task_deps.reads.

cc69b42

Rename a badly-named variable.

38d7e8b

nnethercote closed this Oct 9, 2025

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Oct 9, 2025

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Auto merge of #147508 - nnethercote:TaskDeps-improvements, r=<try>

ec47f3e

`TaskDeps` improvements

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 9, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 9, 2025

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Auto merge of #147508 - nnethercote:TaskDeps-improvements, r=<try>

e4658cf

`TaskDeps` improvements

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bors added a commit that referenced this pull request Oct 15, 2025

Auto merge of #147508 - nnethercote:TaskDeps-improvements, r=saethlin

89342a8

`TaskDeps` improvements Some cleanups and minor perf improvements relating to `TaskDeps`. r? `@saethlin`

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 15, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 15, 2025

bors added a commit that referenced this pull request Oct 16, 2025

Auto merge of #147508 - nnethercote:TaskDeps-improvements, r=saethlin

3b3b2ea

`TaskDeps` improvements Some cleanups and minor perf improvements relating to `TaskDeps`. r? `@saethlin`

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 16, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 17, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 17, 2025

bors merged commit 28c4c7d into rust-lang:master Oct 17, 2025
22 of 25 checks passed

rustbot added this to the 1.92.0 milestone Oct 17, 2025

matthiaskrgr mentioned this pull request Oct 19, 2025

spurious test failures condvar::nonpoison_timeout_nanoseconds #147885

Closed

Mark-Simulacrum added the perf-regression-triaged The performance regression has been triaged. label Oct 21, 2025

TaskDeps improvements #147508

TaskDeps improvements #147508

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Overall result: ❌✅ regressions and improvements - please read the text below

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Test differences

Job duration changes

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Overall result: ❌✅ regressions and improvements - please read the text below

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`TaskDeps` improvements #147508

`TaskDeps` improvements #147508

nnethercote commented Oct 9, 2025 •

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