Introduce `DynSend` and `DynSync` auto trait for parallel compiler by SparrowLii...
source link: https://github.com/rust-lang/rust/pull/107586
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Introduce DynSend and DynSync auto trait for parallel compiler
#107586
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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
added A-query-system Area: The rustc query system (https://rustc-dev-guide.rust-lang.org/query.html) S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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| @@ -952,6 +958,151 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) -> Result<()> { | ||
Ok(()) |
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} |
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fn non_par_analysis(tcx: TyCtxt<'_>) -> Result<()> { |
This code duplication is really unfortunate.
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Author
That's right. Haven't thought of an elegant way to write it yet, but I'll fix that soon
// runtime whether these non-shared data structures actually exist. |
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unsafe impl<'tcx> DynSendSyncCheck for TyCtxt<'tcx> { |
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#[inline] |
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fn check_send_sync(&self) { |
Can you use let GlobalCtxt { a, b, c } = self for exhaustiveness checking?
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Author
Yea, it makes sense!
// Only set by the `-Z threads` compile option |
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pub unsafe fn set_parallel() { |
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let p = SyncUnsafeCell::raw_get(&PARALLEL as *const _); |
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*p = true; |
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} |
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.
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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?).
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OK. I changed to AtomicBool instead. Can you help run a perf?Thanks!
I think we can just use Relaxed, yea
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added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label
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Try build successful - This comment has been minimized.
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Finished benchmarking commit (62ba597): comparison URL. Overall result:
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| 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
Cycles
Results
added perf-regression Performance regressions
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I think there may be two reasons for regression : |
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I've been thinking over how to best approach specialization. I think the dynamic dispatch entry point to 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 |
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In my local test, Also as I guessed, |
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Can we run another perf? Thanks! |
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The latest upstream changes (presumably |
@SparrowLii if I read the comment thread correctly @cjgillot should approve this PR after one last rebase? Thanks! @rustbot author |
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@cjgillot Can it be merged now? : ) I don't have privileges so I need your help |
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@bors r+ rollup=never |
Commit added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion.
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Finished benchmarking commit (dd8ec9c): comparison URL. Overall result: no relevant changes - no action needed@rustbot label: -perf-regression Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)Results CyclesThis benchmark run did not return any relevant results for this metric. Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 660.401s -> 660.339s (-0.01%) |
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