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Improved performance and solved performance regressions of v2 against v1#405

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Improved performance and solved performance regressions of v2 against v1#405
alejandro-vaz wants to merge 4 commits intoservo:v2from
alejandro-vaz:v2

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@alejandro-vaz alejandro-vaz commented Mar 9, 2026

Improvements

This PR solves the performance regressions v2 introduced. Its most meaningful improvements are (in nanoseconds):

  • bench_extend: 80.48 $\to$ 33.35 (+141%)
  • bench_extend_filtered: 82.81 $\to$ 76.71 (+8%)
  • bench_extend_filtered_small: 7.26 $\to$ 5.50 (+32%)
  • bench_extend_from_slice: 82.10 $\to$ 32.65 (+151%)
  • bench_extend_from_slice_small: 9.80 $\to$ 4.85 (+102%)
  • bench_insert_push: 307.51 $\to$ 261.76 (+17%)
  • bench_insert_push_small: 39.03 $\to$ 24.50 (+59%)
  • bench_insert_small: 116.55 $\to$ 89.86 (+30%)
  • bench_push: 277.76 $\to$ 211.13 (+32%)
  • bench_push_small: 41.78 $\to$ 27.19 (+54%)
  • bench_push_vec: 213.06 $\to$ 195.58 (+9%)
  • bench_push_vec_small: 27.75 $\to$ 23.52 (+18%)
  • bench_pushpop: 303.43 $\to$ 214.62 (+41%)
  • bench_pushpop_vec: 143.72 $\to$ 114.65 (+25%)
  • bench_remove_small: 77.25 $\to$ 67.98 (+14%)

Some benchmarks score faster than on the v1 implementation.

Added a test for safe unwind.

Performance

Benchmark V1 Default V1 Spec V2 Curr Def V2 Curr Spec V2 PR Def V2 PR Spec
bench_extend 33.63 32.58 80.48 31.07 33.35 31.80
bench_extend_filtered — — 82.81 81.24 76.71 76.42
bench_extend_filtered_small — — 7.26 7.33 5.50 5.48
bench_extend_from_slice 33.65 33.24 82.10 32.67 32.65 32.71
bench_extend_from_slice_small 5.63 5.44 9.80 4.82 4.85 4.82
bench_extend_from_slice_vec 52.66 52.46 52.62 52.71 52.17 53.27
bench_extend_from_slice_vec_small 13.53 13.63 13.70 13.37 13.43 13.67
bench_extend_small 9.43 11.71 9.35 4.47 11.66 4.40
bench_extend_vec 48.90 50.88 49.41 50.52 49.52 49.83
bench_extend_vec_filtered — — 102.78 105.14 104.71 106.72
bench_extend_vec_filtered_small — — 17.85 17.95 17.98 18.11
bench_extend_vec_small 14.73 13.99 14.19 14.39 13.82 14.82
bench_from_iter 34.13 27.46 28.59 29.87 28.50 29.36
bench_from_iter_small 11.58 4.69 6.62 4.62 6.49 4.61
bench_from_iter_vec 27.80 27.90 28.45 28.70 26.58 28.56
bench_from_iter_vec_small 13.46 12.98 12.87 13.28 12.68 12.80
bench_from_slice 29.24 28.55 28.21 28.80 28.27 27.02
bench_from_slice_small 4.71 4.70 4.53 4.63 4.50 4.63
bench_from_slice_vec 27.84 28.82 28.42 26.29 28.14 28.08
bench_from_slice_vec_small 12.94 12.99 13.12 13.71 12.75 12.87
bench_insert 873.39 904.35 877.77 877.94 867.75 868.96
bench_insert_from_slice 97.47 93.59 — — — —
bench_insert_many 95.76 95.82 — — — —
bench_insert_push 278.25 276.31 307.51 305.03 261.76 261.98
bench_insert_push_small 20.82 20.80 39.03 40.34 24.50 24.47
bench_insert_push_vec 222.78 241.60 228.71 220.42 253.98 213.60
bench_insert_push_vec_small 27.32 34.96 27.57 27.46 31.87 31.70
bench_insert_small 89.16 98.21 116.55 114.64 89.86 90.69
bench_insert_vec 822.34 844.16 815.21 830.29 826.88 809.04
bench_insert_vec_small 111.47 109.28 95.67 93.13 94.67 104.38
bench_macro_from_elem 28.64 28.98 29.01 29.11 29.52 29.76
bench_macro_from_elem_small 7.99 7.92 11.13 7.78 11.17 7.81
bench_macro_from_elem_vec 25.47 26.36 25.72 25.49 25.83 25.76
bench_macro_from_elem_vec_small 12.89 12.14 12.89 12.38 12.65 12.68
bench_macro_from_list 19.10 19.64 19.05 18.64 18.86 19.13
bench_macro_from_list_vec 18.64 18.88 18.62 18.88 21.65 19.13
bench_push 258.01 257.07 277.76 280.67 211.13 210.48
bench_push_small 29.50 29.67 41.78 43.34 27.19 24.86
bench_push_vec 214.09 201.42 213.06 221.32 195.58 199.19
bench_push_vec_small 27.55 23.80 27.75 27.44 23.52 24.04
bench_pushpop 385.46 376.88 303.43 232.75 214.62 214.51
bench_pushpop_vec 114.13 114.47 143.72 114.43 114.65 114.22
bench_remove 666.78 662.11 668.97 665.62 679.51 669.96
bench_remove_small 70.20 70.36 77.25 78.37 67.98 73.69
bench_remove_vec 639.01 642.30 644.72 641.40 636.96 642.31
bench_remove_vec_small 73.35 71.91 73.69 72.25 75.45 74.15

Spec stands for the specialization feature enabled.

@alejandro-vaz alejandro-vaz mentioned this pull request Mar 9, 2026
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alejandro-vaz commented Mar 9, 2026

this closes #404

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alejandro-vaz commented Mar 12, 2026

The issue should be now fixed, I just accidentally removed some unsafe blocks that apparently were truly unsafe in other rust versions

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alejandro-vaz commented Mar 13, 2026

hey, the gh actions workflow is waiting for maintainer approval to start. just leaving this comment here so whenever someone sees it can trigger the rerun (it should now be fine, see above)

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alejandro-vaz commented Mar 13, 2026

it should be now fixed

extend_from_slice wasn't allocating enough capacity sometimes (maybe by one item always?, anyway, I defaulted to reserve(new_length) though it's a bit slower, but works fine), now it's fixed

it does seem that some benchmarks got a bit slower but it's within ranges so it might just be noise (anyway, it'd be 5% at most)

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alejandro-vaz commented Mar 13, 2026

it's ready to be reviewed. also, it closes #404

I'm open to feedback and suggestions

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