[ruby-core:45646] [ruby-trunk - Feature #6002][Rejected] use IO#advise in FileUtils.compare_stream

Issue #6002 has been updated by kosaki (Motohiro KOSAKI).

Status changed from Assigned to Rejected

akr-san, pointed out IO#advise may raise EINVAL exception when linux w/ tmpfs. (see [ruby-dev:45703])

Thus, we can't apply this patch.

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Feature #6002: use IO#advise in FileUtils.compare_stream
https://bugs.ruby-lang.org/issues/6002#change-27246

Author: Glass_saga (Masaki Matsushita)
Status: Rejected
Priority: Normal
Assignee: kosaki (Motohiro KOSAKI)
Category: lib
Target version: 


=begin
I propose to call IO#advise in FileUtils.compare_stream.
It will increase performance.

I created a dummy file:
 dd if=/dev/zero of=dummy bs=1M count=100

Then, I ran the following:

 require 'benchmark'
 require 'fileutils'
 
 path = "dummy"
 
 Benchmark.bm do |x|
   x.report do
     FileUtils.compare_file(path, path)
   end
 end

I freed page cache before each test:
 sudo sysctl -w vm.drop_caches=1

results on Ubuntu 11.10(3.0.0-15-server):

r34527:

 user     system      total        real
    0.050000   0.260000   0.310000 (  0.353097)
 
        user     system      total        real
    0.030000   0.250000   0.280000 (  0.320861)
 
        user     system      total        real
    0.070000   0.250000   0.320000 (  0.391100)

proposal:

 user     system      total        real
   0.050000   0.170000   0.220000 (  0.235541)

       user     system      total        real
   0.020000   0.150000   0.170000 (  0.188613)

       user     system      total        real
   0.030000   0.170000   0.200000 (  0.201237)

It shows the patch increases performance.
=end


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