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cat: avoid unnecessary allocation#11675

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sylvestre merged 1 commit intouutils:mainfrom
oech3:cat-alloc
Apr 12, 2026
Merged

cat: avoid unnecessary allocation#11675
sylvestre merged 1 commit intouutils:mainfrom
oech3:cat-alloc

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@oech3 oech3 commented Apr 6, 2026

Allocate buffer on heap instead of stack for read()/write() show-path which is unnecessary if splice() fast-path succeed.

$ echo 1 > /tmp/1
> taskset -c 0 hyperfine -N --runs 10000 "/tmp/coreutils/target/release/cat-stack /tmp/1" "target/release/cat-heap /tmp/1"
Benchmark 1: /tmp/coreutils/target/release/cat-stack /tmp/1
  Time (mean ± σ):     921.2 µs ±  84.4 µs    [User: 372.9 µs, System: 443.7 µs]
  Range (min … max):   843.0 µs … 3926.9 µs    10000 runs
Benchmark 2: target/release/cat-heap /tmp/1
  Time (mean ± σ):     908.6 µs ± 117.0 µs    [User: 380.6 µs, System: 424.1 µs]
  Range (min … max):   821.4 µs … 4337.6 µs    10000 runs 
Summary
  target/release/cat-heap /tmp/1 ran
    1.01 ± 0.16 times faster than /tmp/coreutils/target/release/cat-stack /tmp/1

related #10832

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github-actions bot commented Apr 6, 2026

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/dd/no-allocate is now being skipped but was previously passing.
Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.
Congrats! The gnu test tests/cut/bounded-memory is now passing!

@oech3 oech3 marked this pull request as ready for review April 6, 2026 07:55
@oech3 oech3 marked this pull request as draft April 6, 2026 08:04
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github-actions bot commented Apr 6, 2026

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/cut-huge-range is now passing!

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oech3 commented Apr 6, 2026

hyperfine is flakey

@oech3 oech3 marked this pull request as ready for review April 6, 2026 08:49
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xtqqczze commented Apr 6, 2026

Switching from a stack allocation to a heap allocation doesn’t avoid allocation...

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oech3 commented Apr 6, 2026 via email

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oech3 commented Apr 6, 2026

I saw more perf difference with 1024 * 1024 by switching to vec. So I think vec's allocation is deffered.

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github-actions bot commented Apr 8, 2026

GNU testsuite comparison:

Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.

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github-actions bot commented Apr 8, 2026

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/cut-huge-range is now passing!

@sylvestre sylvestre merged commit efd0f0c into uutils:main Apr 12, 2026
169 checks passed
@oech3 oech3 deleted the cat-alloc branch April 12, 2026 14:38
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oech3 commented Apr 12, 2026

We might use nightly fill_buf in the future to avoid 0-fill at here.

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xtqqczze commented Apr 12, 2026

We might use nightly fill_buf in the future to avoid 0-fill at here.

Presumably you mean nightly-only Read::read_buf. Might be worth prototyping an implementation to validate this approach.

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@oech3 @xtqqczze @sylvestre