2023-03-14 18:20:35 +00:00
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# Поиск лишних аллокаций
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Для анализа аллокаций в задачах с бенчмарками удобно использовать встроенный в язык профайлер `pprof`.
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Сперва нужно запустить бенчмарк с профайлером
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```
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2023-03-14 18:30:02 +00:00
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✗ go test -v -run=^$ -bench=BenchmarkSprintf -memprofile=mem.out ./varfmt/...
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2023-03-14 18:20:35 +00:00
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goos: linux
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goarch: amd64
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pkg: gitlab.com/slon/shad-go/varfmt
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cpu: Intel(R) Core(TM) i7-8650U CPU @ 1.90GHz
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BenchmarkSprintf
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BenchmarkSprintf/small
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BenchmarkSprintf/small-8 19429222 62.93 ns/op 2 B/op 1 allocs/op
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BenchmarkSprintf/small_string
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BenchmarkSprintf/small_string-8 13282659 84.48 ns/op 16 B/op 1 allocs/op
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BenchmarkSprintf/big
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BenchmarkSprintf/big-8 20089 62372 ns/op 16388 B/op 1 allocs/op
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PASS
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ok gitlab.com/slon/shad-go/varfmt 4.363s
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```
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Сэмплы профайлера будут записаны в бинарный файл `mem.out`.
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Этот файл можно открыть командой
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```
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✗ go tool pprof mem.out
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File: varfmt.test
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Type: alloc_space
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Time: Mar 14, 2023 at 9:07pm (MSK)
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Entering interactive mode (type "help" for commands, "o" for options)
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(pprof)
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```
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В результате откроется интерактивная среда, в которой есть всякие команды, например `help`.
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Чтобы узнать как запускать конкретную команду нужно вызвать `help` для неё
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```
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(pprof) help top
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Outputs top entries in text form
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Usage:
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top [n] [focus_regex]* [-ignore_regex]* [-cum] >f
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Include up to n samples
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Include samples matching focus_regex, and exclude ignore_regex.
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-cum sorts the output by cumulative weight
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Optionally save the report on the file f
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```
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Команда `top` покажет места, где суммарно было больше всего аллокаций
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```
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(pprof) top -cum
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Showing nodes accounting for 715.73MB, 99.37% of 720.23MB total
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Dropped 24 nodes (cum <= 3.60MB)
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flat flat% sum% cum cum%
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715.73MB 99.37% 99.37% 716.73MB 99.51% fmt.Sprintf
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0 0% 99.37% 716.73MB 99.51% gitlab.com/slon/shad-go/varfmt.BenchmarkSprintf.func1
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0 0% 99.37% 716.73MB 99.51% testing.(*B).launch
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0 0% 99.37% 716.73MB 99.51% testing.(*B).runN
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(pprof)
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```
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Команда `svg` сдампит `top` в картинку.
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```
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(pprof) svg
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Generating report in profile001.svg
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```
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Команда `list` покажет строчки, в которых происходят аллокации
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```
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(pprof) list fmt.Sprintf
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Total: 720.23MB
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ROUTINE ======================== fmt.Sprintf in /usr/local/go/src/fmt/print.go
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715.73MB 716.73MB (flat, cum) 99.51% of Total
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. . 213: return Fprintf(os.Stdout, format, a...)
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. . 214:}
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. . 215:
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. . 216:// Sprintf formats according to a format specifier and returns the resulting string.
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. . 217:func Sprintf(format string, a ...any) string {
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. 512kB 218: p := newPrinter()
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. . 219: p.doPrintf(format, a)
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715.73MB 715.73MB 220: s := string(p.buf)
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. 512.50kB 221: p.free()
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. . 222: return s
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. . 223:}
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. . 224:
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. . 225:// Appendf formats according to a format specifier, appends the result to the byte
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. . 226:// slice, and returns the updated slice.
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```
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