YAPC::EU 2015

1. Optimize Perl5 code
for performance freaks.
Kenta SATO (@karupanerura)
YAPC::EU 2015

2. Hello, YAPC::EU!

3. About me
• Kenta SATO (@karupanerura)
• Senior Engineer at Mobile Factory, Inc.
• WebApp/iOS/Android/Operation/etc..
• Perl/Swift/Kotlin/Java/Crystal/XS/C99/etc..
• Gotanda.pm Author

4. CPAN (PAUSE: KARUPA)
• Time::Strptime
• Geo::Hex::V3::XS
• Test::SharedObject
• Plack::App::Vhost
• etc..

5. Gotanda.pm

6. Gotanda.pm
Granada.pm

7. Gotanda.pm
Granada.pm
a little different,
but mostly same!

8. Nice to meet you :)

9. Optimize Perl5 code
for performance freaks.

10. What about of
performance?

11. Perl5 code performance

12. for performance freaks :)

13. I'll talk about …
• Perl5 code
• Regular expressions
• Variable access
• Conditional branch

14. I’ll *NOT* talk about …
• Architecture
• Database
• I/O Multiplexing
• Concurrency
• etc..

15. $example = “strptime”

16. strptime(3)
• Parse date time string using arbitrary format
• e.g.) “%Y-%m-%d %H:%M:%S”
=> “2015-09-04 12:00:00”

17. Choices in Perl5
• DateTime::Format::Strptime (PP)
• Time::Piece->strptime (XS)
• POSIX::strptime (XS)
• Time::Strptime (PP)
• Time::Moment (fixed format but very fast)

18. Time::Strptime
• Pure Perl implementation
• If Time::TZOffset is installed, make it faster
• Using Time::Local for caluclating epoch
• Using system timezone
• Using system locale

19. Benchmark
DEMO

20. tp=Time::Piece(XS)
ts=Time::Strptime(PP)

21. (In this case)
Pure Perl is
faster than XS!

22. NOTE:
Benchmark environment
• https://github.com/karupanerura/Time-
Strptime/wiki/Benckmark-result

23. Why is Time::Strptime faster?

24. tuning tips
• Suppress memory copy
• Optimize regular expressions
• Instance cache
• String eval

25. Suppress memory copy
• Use constant.pm if possible
• for constant folding
• Use perl 5.20 or later
• String COW is available
• experimental::refaliasing

26. experimental::refaliasing
• Enables aliasing via assignment to references
• Example: my $bar = $foo
• Makes alias $bar to $foo
• (pointer to same memory)
• Available on perl 5.22 or later

27. experimental::refaliasing
• But, Not fast… (why…?)
• Copying is 63% faster than refaliasing
• When copying|refaliasing IV value
• I believe that refaliasing will be faster than
copying in near future :)

28. Optimize regular expressions
• Less slow expressions
• Character Class < Quantifiers < Grouping
• e.g.) Less matching patterns of regexp
• e.g.) /A[0-5][0-9]z/m
• This is 6% faster than /A[0-9]{2}z/m

29. Optimize regular expressions
• Approach: Loose matching
• Example: /A[0-9]{4}-[0-9]{2}-[0-9]{2}z/m
• ↑ is 11%~16% faster than ↓
• /A[0-9]{4}-(?:(?:0[1-9]|1[0-2])-(?:0[1-9]|[12][0-9]|3[01])z/m
• Cons: Unsafe..

30. Instance cache
• Time::Strptime reuses instances
• Often times the same format is used
• So cached instance can be used
• Pay format parsing cost only once
• Caching is enabled by default

31. String eval
• Used to avoid conditional statements.
• Pay the cost of generating code instead of at
runtime
• (DEMO)

32. String eval
• Warning: very DANGEROUS!!
• If you use it in your code, you should write
many tests

33. CONCLUSION

34. CONCLUSION
• XS module is generally fast
• Optimized Pure Perl code can be faster
• String eval is helpful, but beware!

35. Any questions?
(Easy english please…)
or mention to
@karupanerura
on Twitter