BTree: lazily locate leaves in rangeless iterators by ssomers · Pull Request #86031 · rust-lang/rust

ssomers · 2021-06-05T17:32:28Z

BTree iterators always locate both the first and last leaf edge and often only need either one, i.e., whenever they are traversed in a single direction, like in for-loops and in the common use of iter().next() or iter().next_back() to retrieve the first or last key/value-pair (#62924). It's fairly easy to avoid because the iterators with this disadvantage already are quite separate from other iterators.

r? @Mark-Simulacrum

ssomers · 2021-06-05T17:48:34Z

About alloc's own benches:

They're generally positive, but who knows what that means in other code.
The btree::map::iter_X benches obviously benefit, but they're quite artificial now since they merely invoke iter().
In small maps, or intersection benches that can quickly bail out, the "descend" to the leaf node didn't take long anyway and the extra flags that take care of avoiding it slow down.
The btree::map::first_and_last_X_stable benches show that legacy iter().next() calls are twice as fast, but they are still considerably slower than the nightly first and last functions promoted in Tracking issue for map_first_last: first/last methods on BTreeSet and BTreeMap #62924. No idea why.

 name mid ns/iter new ns/iter diff ns/iter diff % speedup
btree::map::clone_fat_val_100 10,772 11,452 680 6.31% x 0.94
btree::map::clone_fat_val_100_and_clear 10,746 10,737 -9 -0.08% x 1.00
btree::map::clone_fat_val_100_and_drain_all 44,356 44,764 408 0.92% x 0.99
btree::map::clone_fat_val_100_and_drain_half 31,685 31,179 -506 -1.60% x 1.02
btree::map::clone_fat_val_100_and_into_iter 9,913 10,070 157 1.58% x 0.98
btree::map::clone_fat_val_100_and_pop_all 54,122 54,185 63 0.12% x 1.00
btree::map::clone_fat_val_100_and_remove_all 45,772 46,705 933 2.04% x 0.98
btree::map::clone_fat_val_100_and_remove_half 29,832 29,763 -69 -0.23% x 1.00
btree::map::clone_slim_100 4,303 4,309 6 0.14% x 1.00
btree::map::clone_slim_100_and_clear 4,255 4,231 -24 -0.56% x 1.01
btree::map::clone_slim_100_and_drain_all 6,091 6,150 59 0.97% x 0.99
btree::map::clone_slim_100_and_drain_half 5,370 5,307 -63 -1.17% x 1.01
btree::map::clone_slim_100_and_into_iter 4,303 4,240 -63 -1.46% x 1.01
btree::map::clone_slim_100_and_pop_all 6,321 6,144 -177 -2.80% x 1.03
btree::map::clone_slim_100_and_remove_all 7,097 6,901 -196 -2.76% x 1.03
btree::map::clone_slim_100_and_remove_half 5,590 5,575 -15 -0.27% x 1.00
btree::map::clone_slim_10k 181,173 182,340 1,167 0.64% x 0.99
btree::map::clone_slim_10k_and_clear 179,972 185,704 5,732 3.18% x 0.97
btree::map::clone_slim_10k_and_drain_all 375,875 372,945 -2,930 -0.78% x 1.01
btree::map::clone_slim_10k_and_drain_half 316,386 313,505 -2,881 -0.91% x 1.01
btree::map::clone_slim_10k_and_into_iter 184,300 184,380 80 0.04% x 1.00
btree::map::clone_slim_10k_and_pop_all 406,045 406,948 903 0.22% x 1.00
btree::map::clone_slim_10k_and_remove_all 537,710 482,480 -55,230 -10.27% x 1.11
btree::map::clone_slim_10k_and_remove_half 482,560 491,320 8,760 1.82% x 0.98
btree::map::find_rand_100 9 11 2 22.22% x 0.82
btree::map::find_rand_10_000 52 53 1 1.92% x 0.98
btree::map::find_seq_100 11 12 1 9.09% x 0.92
btree::map::find_seq_10_000 36 35 -1 -2.78% x 1.03
btree::map::first_and_last_0_nightly 9 9 0 0.00% x 1.00
btree::map::first_and_last_0_stable 24 24 0 0.00% x 1.00
btree::map::first_and_last_100_nightly 33 48 15 45.45% x 0.69
btree::map::first_and_last_100_stable 236 102 -134 -56.78% x 2.31
btree::map::first_and_last_10k_nightly 68 60 -8 -11.76% x 1.13
btree::map::first_and_last_10k_stable 259 121 -138 -53.28% x 2.14
btree::map::insert_rand_100 38 38 0 0.00% x 1.00
btree::map::insert_rand_10_000 38 38 0 0.00% x 1.00
btree::map::insert_seq_100 46 46 0 0.00% x 1.00
btree::map::insert_seq_10_000 93 95 2 2.15% x 0.98
btree::map::iter_0 1,254 1,755 501 39.95% x 0.71
btree::map::iter_1 4,013 1,755 -2,258 -56.27% x 2.29
btree::map::iter_100 4,388 1,724 -2,664 -60.71% x 2.55
btree::map::iter_10k 5,952 1,755 -4,197 -70.51% x 3.39
btree::map::iter_1m 8,179 1,755 -6,424 -78.54% x 4.66
btree::map::iteration_1000 4,092 3,850 -242 -5.91% x 1.06
btree::map::iteration_100000 526,900 464,360 -62,540 -11.87% x 1.13
btree::map::iteration_20 65 60 -5 -7.69% x 1.08
btree::map::iteration_mut_1000 4,250 4,011 -239 -5.62% x 1.06
btree::map::iteration_mut_100000 532,400 476,360 -56,040 -10.53% x 1.12
btree::map::iteration_mut_20 66 62 -4 -6.06% x 1.06
btree::map::range_included_excluded 393,385 406,255 12,870 3.27% x 0.97
btree::map::range_included_included 401,615 402,760 1,145 0.29% x 1.00
btree::map::range_included_unbounded 137,408 139,191 1,783 1.30% x 0.99
btree::map::range_unbounded_unbounded 45,399 42,853 -2,546 -5.61% x 1.06
btree::map::range_unbounded_vs_iter 45,758 18,328 -27,430 -59.95% x 2.50
btree::set::clone_100 1,408 1,401 -7 -0.50% x 1.00
btree::set::clone_100_and_clear 1,410 1,411 1 0.07% x 1.00
btree::set::clone_100_and_drain_all 2,960 2,950 -10 -0.34% x 1.00
btree::set::clone_100_and_drain_half 2,309 2,304 -5 -0.22% x 1.00
btree::set::clone_100_and_into_iter 1,436 1,557 121 8.43% x 0.92
btree::set::clone_100_and_pop_all 2,704 2,713 9 0.33% x 1.00
btree::set::clone_100_and_remove_all 3,706 3,561 -145 -3.91% x 1.04
btree::set::clone_100_and_remove_half 2,410 2,469 59 2.45% x 0.98
btree::set::clone_10k 170,150 166,192 -3,958 -2.33% x 1.02
btree::set::clone_10k_and_clear 170,544 170,363 -181 -0.11% x 1.00
btree::set::clone_10k_and_drain_all 326,732 323,010 -3,722 -1.14% x 1.01
btree::set::clone_10k_and_drain_half 282,630 281,396 -1,234 -0.44% x 1.00
btree::set::clone_10k_and_into_iter 171,660 182,752 11,092 6.46% x 0.94
btree::set::clone_10k_and_pop_all 314,910 310,033 -4,877 -1.55% x 1.02
btree::set::clone_10k_and_remove_all 455,900 415,210 -40,690 -8.93% x 1.10
btree::set::clone_10k_and_remove_half 446,190 438,070 -8,120 -1.82% x 1.02
btree::set::difference_random_100_vs_100 1,009 1,077 68 6.74% x 0.94
btree::set::difference_random_100_vs_10k 2,128 2,116 -12 -0.56% x 1.01
btree::set::difference_random_10k_vs_100 69,723 76,655 6,932 9.94% x 0.91
btree::set::difference_random_10k_vs_10k 217,273 227,112 9,839 4.53% x 0.96
btree::set::difference_staggered_100_vs_100 1,111 1,266 155 13.95% x 0.88
btree::set::difference_staggered_100_vs_10k 2,050 2,080 30 1.46% x 0.99
btree::set::difference_staggered_10k_vs_10k 110,005 126,791 16,786 15.26% x 0.87
btree::set::intersection_100_neg_vs_100_pos 17 28 11 64.71% x 0.61
btree::set::intersection_100_neg_vs_10k_pos 18 30 12 66.67% x 0.60
btree::set::intersection_100_pos_vs_100_neg 17 28 11 64.71% x 0.61
btree::set::intersection_100_pos_vs_10k_neg 18 30 12 66.67% x 0.60
btree::set::intersection_10k_neg_vs_100_pos 18 29 11 61.11% x 0.62
btree::set::intersection_10k_neg_vs_10k_pos 19 32 13 68.42% x 0.59
btree::set::intersection_10k_pos_vs_100_neg 18 29 11 61.11% x 0.62
btree::set::intersection_10k_pos_vs_10k_neg 19 32 13 68.42% x 0.59
btree::set::intersection_random_100_vs_100 717 582 -135 -18.83% x 1.23
btree::set::intersection_random_100_vs_10k 1,882 1,896 14 0.74% x 0.99
btree::set::intersection_random_10k_vs_100 1,861 1,852 -9 -0.48% x 1.00
btree::set::intersection_random_10k_vs_10k 166,006 164,202 -1,804 -1.09% x 1.01
btree::set::intersection_staggered_100_vs_100 641 617 -24 -3.74% x 1.04
btree::set::intersection_staggered_100_vs_10k 1,770 1,847 77 4.35% x 0.96
btree::set::intersection_staggered_10k_vs_10k 63,001 61,322 -1,679 -2.67% x 1.03
btree::set::is_subset_100_vs_100 626 621 -5 -0.80% x 1.01
btree::set::is_subset_100_vs_10k 1,441 1,349 -92 -6.38% x 1.07
btree::set::is_subset_10k_vs_100 2 2 0 0.00% x 1.00
btree::set::is_subset_10k_vs_10k 63,428 61,306 -2,122 -3.35% x 1.03

Mark-Simulacrum · 2021-06-07T00:20:18Z

@bors try @rust-timer queue

rust-timer · 2021-06-07T00:20:19Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

bors · 2021-06-07T00:20:26Z

⌛ Trying commit 9e1ac543d134a115fe253691eb9b137192560b7a with merge ae3cf1a90b2081be4fab0ca50bf8e1c75877a29d...

bors · 2021-06-07T01:05:39Z

☀️ Try build successful - checks-actions
Build commit: ae3cf1a90b2081be4fab0ca50bf8e1c75877a29d (ae3cf1a90b2081be4fab0ca50bf8e1c75877a29d)

rust-timer · 2021-06-07T01:05:41Z

Queued ae3cf1a90b2081be4fab0ca50bf8e1c75877a29d with parent 35fff69, future comparison URL.

rust-timer · 2021-06-07T04:21:34Z

Finished benchmarking try commit (ae3cf1a90b2081be4fab0ca50bf8e1c75877a29d): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

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

ssomers · 2021-06-21T07:56:01Z

Last commits fix variance and try to maintain #[inline] placement, which seems to dominate performance.

bors · 2021-07-08T18:05:21Z

☔ The latest upstream changes (presumably #86520) made this pull request unmergeable. Please resolve the merge conflicts.

ssomers · 2021-07-22T10:10:50Z

@rustbot label: +S-waiting-on-review -S-waiting-on-author

Mark-Simulacrum · 2021-08-01T14:17:59Z

@bors try @rust-timer queue

Seems generally OK, though I wonder if the performance regressions are largely down to slightly more complicated code. The theoretical improvement from avoiding the extra traversal (in practice usually just one, I imagine; most iterators are likely traversed at least a few times) is worth the possible compile time overheads...

rust-timer · 2021-08-01T14:18:00Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

bors · 2021-08-01T14:18:11Z

⌛ Trying commit 35d02e2 with merge d3ac1a943e62f13e360607ac74b33332a0916f76...

bors · 2021-08-01T15:09:52Z

☀️ Try build successful - checks-actions
Build commit: d3ac1a943e62f13e360607ac74b33332a0916f76 (d3ac1a943e62f13e360607ac74b33332a0916f76)

rust-timer · 2021-08-01T15:09:54Z

Queued d3ac1a943e62f13e360607ac74b33332a0916f76 with parent 8d57c0a, future comparison URL.

rust-timer · 2021-08-01T17:37:48Z

Finished benchmarking try commit (d3ac1a943e62f13e360607ac74b33332a0916f76): comparison url.

Summary: This benchmark run did not return any significant changes.

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up.

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

Mark-Simulacrum · 2021-08-01T17:43:47Z

@bors r+

bors · 2021-08-01T17:43:48Z

📌 Commit 35d02e2 has been approved by Mark-Simulacrum

ssomers · 2021-08-01T19:24:01Z

avoiding the extra traversal (in practice usually just one, I imagine; most iterators are likely traversed at least a few times)

I don't understand what you're referring to (but I don't have to). It's always about just one (multi-level) traversal, and one that's going to be done anyway if iterating to the end. For huge trees, iterating to the end could save multiple memory fetches of nodes that get bored in the cache and leave, before they're read for real, but then it's a huge tree anyway, and just traversing to the fixed first leaf node is wasteful.

As to the slightly more complicated code, it should allow reverting #81486.

bors · 2021-08-01T21:45:35Z

⌛ Testing commit 35d02e2 with merge cd5a90f...

bors · 2021-08-02T00:13:35Z

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing cd5a90f to master...

…r=Mark-Simulacrum BTree: merge the complication introduced by rust-lang#81486 and rust-lang#86031 Also: - Deallocate the last few tree nodes as soon as an `into_iter` iterator steps beyond the end, instead of waiting around for the drop of the iterator (just to share more code). - Symmetric code for backward iteration. - Mark unsafe the methods on dying handles, modelling dying handles after raw pointers: it's the caller's responsibility to use them safely. r? `@Mark-Simulacrum`

rust-highfive assigned Mark-Simulacrum Jun 5, 2021

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ssomers marked this pull request as ready for review June 6, 2021 12:28

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 7, 2021

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ssomers marked this pull request as draft June 9, 2021 10:54

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ssomers marked this pull request as ready for review June 21, 2021 07:51

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ssomers marked this pull request as ready for review June 26, 2021 11:43

BTree: lazily locate leaves in rangeless iterators
35d02e2

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Mark-Simulacrum mentioned this pull request Aug 1, 2021
comment summary does not match significant changes filter on comparison pages rust-lang/rustc-perf#952
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ssomers mentioned this pull request Aug 1, 2021
Tracking issue for map_first_last: first/last methods on BTreeSet and BTreeMap #62924
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bors added the merged-by-bors This PR was explicitly merged by bors. label Aug 2, 2021

bors merged commit cd5a90f into rust-lang:masterAug 2, 2021

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bors mentioned this pull request Aug 2, 2021
Port clippy lint redundant_field_names to compiler #87512
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ssomers deleted the btree_lazy_iterator branch August 2, 2021 08:54

Eh2406 mentioned this pull request Aug 6, 2021
from and as RangeBounds pubgrub-rs/pubgrub#105
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