build: faster newLinesIndices via bytes.IndexByte and buffer re-use #680
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This is quite fast, so I don't this the speed improvements are that important. However, the memory usage improvements are likely noticeable due to less work the GC needs to do. Also I recently instrumented the time taken by the ctags parser and didn't include the time taken by tagsToSections. I think given the speed of this that is likely the correct call. If we are slow here it will be ctags not this conversion code. |
jtibshirani
approved these changes
Nov 6, 2023
On my machine this reduces wall clock time of BenchmarkTagsToSections by
38%. This is faster since bytes.IndexByte relies on CPU specific
optimizations to find the next new line (eg uses AVX2 if available).
goos: linux
goarch: amd64
pkg: github.com/sourcegraph/zoekt/build
cpu: AMD Ryzen 9 5950X 16-Core Processor
old time/op new time/op delta
188µs ± 7% 117µs ± 4% -37.96% (p=0.000 n=10+10)
old alloc/op new alloc/op delta
79.3kB ± 0% 79.3kB ± 0% ~ (all equal)
old allocs/op new allocs/op delta
443 ± 0% 443 ± 0% ~ (all equal)
Test Plan: go test -bench BenchmarkTagsToSections
I noticed in the profiler a nonsignificant chunk in the garbage
collector. The slice built by newLinesIndices is allocated and thrown
away for each call to tagsToSections. This means we can re-use it which
this commit implements by introducing a struct storing the buffer. We
now use this buffer per shard of symbols we analyse.
Even with the improvements of the previous commit, this further improves
performance by 13% and halves memory use:
$ benchstat after.txt after2.txt
old time/op new time/op delta
117µs ± 4% 101µs ± 3% -13.12% (p=0.000 n=10+10)
old alloc/op new alloc/op delta
79.3kB ± 0% 36.3kB ± 0% -54.24% (p=0.000 n=9+10)
old allocs/op new allocs/op delta
443 ± 0% 441 ± 0% -0.45% (p=0.000 n=10+10)
Test Plan: go test -bench BenchmarkTagsToSections
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See the individual commits for an explanation. The overall performance improvement of BenchmarkTagsToSections on my machine is: