From: "tenderlovemaking (Aaron Patterson) via ruby-core" <ruby-core@...>
Date: 2023-09-20T21:03:48+00:00
Subject: [ruby-core:114852] [Ruby master Bug#19890] File#realine(chomp: true) slower/more allocations than readline.chomp!

Issue #19890 has been updated by tenderlovemaking (Aaron Patterson).





Dan0042 (Daniel DeLorme) wrote in #note-6:

> Eregon (Benoit Daloze) wrote in #note-5:

> > There such a functionality would cost an extra allocation per call (the special variables objects is passed to the callee and that forces the allocation), which is a significant performance cost.

> 

> I have to say there's too many things I don't understand at all in this. The special variables object is passed from the caller to the callee, not the other way? Does that mean a special variables object is allocated for any method call that *might* result in special variables, such as `#send` ? I'm quite confused.



I'm not sure how it's implemented in TruffleRuby, but in CRuby the special variable object has reference _location_ allocated on the Ruby stack (in the environment).  The svar object itself is lazily allocated only when necessary.  So the callee (IO#readline for example) will end up causing the special variable object to be allocated [here](https://github.com/tenderlove/ruby/blob/43c5fde486c7f6183dab9eacc22261e4cea8acd8/vm_insnhelper.c#L623-L625).

 

> Well, regardless of how it is implemented internally, I think that prepending a module (as in my LogRegexpPerformance example) should be transparent to pseudo-globals. I'm sure there's a way to handle that efficiently even in TruffleRuby.



Seems like a language level change, and I don't have any opinions on it ����



----------------------------------------

Bug #19890: File#realine(chomp: true) slower/more allocations than readline.chomp!

https://bugs.ruby-lang.org/issues/19890#change-104698



* Author: segiddins (Samuel Giddins)

* Status: Open

* Priority: Normal

* ruby -v: 3.2.2

* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

----------------------------------------

On ruby 3.2.2 running the following script:



``` ruby

#!/usr/bin/env ruby



require 'rubygems'

require 'bundler/inline'



puts RUBY_VERSION



gemfile do

  source "https://rubygems.org"

  gem "benchmark-ipsa"

end



Benchmark.ipsa do |x|

  x.report("f.readline(chomp: true)") do

    File.open("/usr/share/dict/words") do |f|

      f.readline(chomp: true) until f.eof?

    end

  end

  

  x.report("f.readline.chomp!") do

    File.open("/usr/share/dict/words") do |f|

      until f.eof?

        s = f.readline

        s.chomp!

        s

      end

    end

  end

  

  x.report("f.readline.chomp") do

    File.open("/usr/share/dict/words") do |f|

      until f.eof?

        f.readline.chomp

      end

    end

  end

  

  x.compare!

end

```



I get the following (surprising) result:



```

3.2.2

Allocations -------------------------------------

	f.readline(chomp: true)

                      707931/1  alloc/ret       50/1  strings/ret

   f.readline.chomp!  235979/1  alloc/ret       50/1  strings/ret

    f.readline.chomp  471955/1  alloc/ret       50/1  strings/ret

Warming up --------------------------------------

f.readline(chomp: true)

                         1.000  i/100ms

   f.readline.chomp!     2.000  i/100ms

    f.readline.chomp     2.000  i/100ms

Calculating -------------------------------------

f.readline(chomp: true)

                         16.165  (�� 6.2%) i/s -     81.000 

   f.readline.chomp!     25.246  (�� 7.9%) i/s -    126.000 

    f.readline.chomp     20.997  (�� 9.5%) i/s -    106.000 



Comparison:

   f.readline.chomp!:       25.2 i/s

    f.readline.chomp:       21.0 i/s - 1.20x slower

f.readline(chomp: true):       16.2 i/s - 1.56x slower

```



I would expect `File#readline(chomp: true)` to be comparable to `s = f.readline; s.chomp!; s` at a bare minimum, but it is slower and has more allocations even than `readline.chomp`









-- 

https://bugs.ruby-lang.org/

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