Introduce `DynSend` and `DynSync` auto trait for parallel compiler #107586

SparrowLii · 2023-02-02T07:22:59Z

part of parallel-rustc #101566

This PR introduces DynSend / DynSync trait and FromDyn / IntoDyn structure in rustc_data_structure::marker. FromDyn can dynamically check data structures for thread safety when switching to parallel environments (such as calling par_for_each_in). This happens only when -Z threads > 1 so it doesn't affect single-threaded mode's compile efficiency.

r? @cjgillot

SparrowLii · 2023-02-02T07:28:51Z

cc @Mark-Simulacrum @m-ou-se @bjorn3 @Zoxc @Nilstrieb

Noratrieb · 2023-02-02T08:11:17Z

compiler/rustc_interface/src/passes.rs

@@ -952,6 +958,151 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) -> Result<()> {
    Ok(())
 }

+fn non_par_analysis(tcx: TyCtxt<'_>) -> Result<()> {


This code duplication is really unfortunate.

That's right. Haven't thought of an elegant way to write it yet, but I'll fix that soon

Noratrieb · 2023-02-02T08:13:26Z

compiler/rustc_middle/src/ty/context.rs

+// runtime whether these non-shared data structures actually exist.
+unsafe impl<'tcx> DynSendSyncCheck for TyCtxt<'tcx> {
+    #[inline]
+    fn check_send_sync(&self) {


Can you use let GlobalCtxt { a, b, c } = self for exhaustiveness checking?

Yea, it makes sense!

WaffleLapkin · 2023-02-02T08:43:56Z

compiler/rustc_data_structures/src/sync.rs

+// Only set by the `-Z threads` compile option
+pub unsafe fn set_parallel() {
+    let p = SyncUnsafeCell::raw_get(&PARALLEL as *const _);
+    *p = true;
+}


First of all, it would be great to have a doc comment here, especially given that this is an unsafe function. Second of all, at first glance it seems like this can be more simply written as *PARALLEL.get() = true, am I missing something? Lastly, is is_parallel hot? Can we use an AtomicUsize instead?

Even if it's a little hot, it's unlikely that an atomic integer will have a performance impact, since this is just reading from it.

Thanks for the review! PARALLEL will only be set once, so I want to take advantage of this to minimize the cost of reading it. with_context_opt might be hot, but I doubt the necessary to check thread safety here. Except this I think is_parallel() is not hot, since it is only used in relatively top-level logic to determine whether to switch to a parallel environment.

You should first benchmark it before going for the more unsafe variant. Atomics have no to minimal overhead depending on the exact use and ordering (which I think can be relaxed here because we don't need to sync any other writes?).

OK. I changed to AtomicBool instead. Can you help run a perf?Thanks!
I think we can just use Relaxed, yea

Noratrieb · 2023-02-02T11:50:27Z

@bors try @rust-timer queue

bors · 2023-02-02T11:50:36Z

⌛ Trying commit 4086ebae9c6b917e51b0f314c18a3dfd032d0e14 with merge 62ba597a41741055fcf131dcee8b691cc9445515...

bors · 2023-02-02T13:59:05Z

☀️ Try build successful - checks-actions
Build commit: 62ba597a41741055fcf131dcee8b691cc9445515 (62ba597a41741055fcf131dcee8b691cc9445515)

rust-timer · 2023-02-02T15:18:58Z

Finished benchmarking commit (62ba597a41741055fcf131dcee8b691cc9445515): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.3%, 1.2%]	134
Regressions ❌ (secondary)	0.7%	[0.1%, 1.9%]	77
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.3%, 1.2%]	134

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.2%, 2.7%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-2.8%, -1.6%]	4
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.7%, 1.3%]	7
Regressions ❌ (secondary)	2.2%	[1.4%, 2.8%]	22
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.0%	[0.7%, 1.3%]	7

SparrowLii · 2023-02-02T16:28:11Z

I think there may be two reasons for regression :
1 multiple if let Some(shared_data) = shared_data.as_ref() in graph.rs.
2 is_parallel() was hot and inefficient.
I'll try to fix them tomorrow

Zoxc · 2023-02-02T19:42:52Z

I've been thinking over how to best approach specialization. I think the dynamic dispatch entry point to rustc_query_impl would be a good place to branch. Using proof objects instead of GAT seems more flexible, at least for locks. I can write up some details on those later.

It seems like a good idea to land locks with a runtime switch first so there is an optimized baseline to compare with specialization. I suggest finishing my branch by extracting just the lock implementation and moving it to a new lock module under sync. You can also add a mode module with a global atomic with 3 states (uninit, on, off). Use a compare and swap to ensure it can only move from uninit to one of the other states. I'm not quite sure what's going on with the DynSendSyncCheck trait, but the manual listing of fields is a bit awkward. We can however literally copy Send and Sync from the standard library and I'd suggest doing so, placing them in a marker module under sync with a rename.

SparrowLii · 2023-02-03T09:30:26Z

In my local test, is_parallel() is to be the main cause of regression. After I changed it to const fn and always return false, the regression was not visible. In addition, the performance of AtomicBool, SyncUnsafeCell, and static mut is not much different.

Also as I guessed, with_context_opt is hot, calling is_parallel() in it looks like the main reason.

SparrowLii · 2023-02-03T09:47:26Z

Can we run another perf? Thanks!

Noratrieb · 2023-02-03T09:55:59Z

@bors try @rust-timer queue

bors · 2023-02-03T09:56:09Z

⌛ Trying commit b2d7910a011fe52c5ab434c695a5caf1a5602725 with merge 2949dcde96d9502e79a5af27f252db8c97e8533e...

bors · 2023-02-03T12:49:39Z

☀️ Try build successful - checks-actions
Build commit: 2949dcde96d9502e79a5af27f252db8c97e8533e (2949dcde96d9502e79a5af27f252db8c97e8533e)

bors · 2023-04-18T00:37:57Z

☔ The latest upstream changes (presumably #110243) made this pull request unmergeable. Please resolve the merge conflicts.

apiraino · 2023-05-03T16:31:19Z

@SparrowLii if I read the comment thread correctly @cjgillot should approve this PR after one last rebase? Thanks!

@rustbot author

SparrowLii · 2023-05-06T03:32:41Z

@cjgillot Can it be merged now? : ) I don't have privileges so I need your help

cjgillot · 2023-05-13T12:53:06Z

@bors r+ rollup=never

bors · 2023-05-13T12:53:08Z

📌 Commit d7e3e5b has been approved by cjgillot

It is now in the queue for this repository.

bors · 2023-05-13T13:47:56Z

⌛ Testing commit d7e3e5b with merge dd8ec9c...

bors · 2023-05-13T16:26:18Z

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing dd8ec9c to master...

rust-timer · 2023-05-13T17:42:04Z

Finished benchmarking commit (dd8ec9c): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Cycles

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

Binary size

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

Bootstrap: 660.401s -> 660.339s (-0.01%)

rustbot assigned cjgillot Feb 2, 2023

Noratrieb reviewed Feb 2, 2023

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WaffleLapkin reviewed Feb 2, 2023

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SparrowLii force-pushed the parallel-query branch from fc5e931 to 4086eba Compare February 2, 2023 11:31

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Feb 2, 2023

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SparrowLii force-pushed the parallel-query branch 3 times, most recently from 25b4906 to d8ca8e6 Compare April 10, 2023 01:54

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 3, 2023

SparrowLii added 6 commits May 6, 2023 09:34

introduce DynSend and DynSync auto trait

b9746ce

fix some nits

261b727

fix parallel!

f196e27

rename relative names in sync

9f8ab2a

correct literals for dyn thread safe

089a388

correct import of owned_slice

bffccdd

SparrowLii force-pushed the parallel-query branch from d8ca8e6 to bffccdd Compare May 6, 2023 02:22

add DynSend / DynSync for CopyTaggedPtr

d7e3e5b

cjgillot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 7, 2023

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 May 13, 2023

bors added the merged-by-bors This PR was explicitly merged by bors. label May 13, 2023

bors merged commit dd8ec9c into rust-lang:master May 13, 2023

rustbot added this to the 1.71.0 milestone May 13, 2023

SparrowLii mentioned this pull request Jul 5, 2023

Tracking Issue for Parallel Rustc Front-end #113349

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SparrowLii mentioned this pull request Jul 12, 2023

Don't require each rustc_interface tool to opt-in to parallel_compiler #113606

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Introduce `DynSend` and `DynSync` auto trait for parallel compiler #107586

Introduce `DynSend` and `DynSync` auto trait for parallel compiler #107586

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Introduce DynSend and DynSync auto trait for parallel compiler #107586

Introduce DynSend and DynSync auto trait for parallel compiler #107586

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Overall result: ❌ regressions - ACTION NEEDED

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Overall result: no relevant changes - no action needed

Introduce `DynSend` and `DynSync` auto trait for parallel compiler #107586

Introduce `DynSend` and `DynSync` auto trait for parallel compiler #107586

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