[ruby-core:42627] [ruby-trunk - Feature #5995][Assigned] calling io_advise_internal() in read_all()

Issue #5995 has been updated by Yusuke Endoh.

Status changed from Open to Assigned
Assignee set to Motohiro KOSAKI

Hello,

2012/2/14 Motohiro KOSAKI <[e-mail]>:
> Huh? fadvise() is a hint for _future_ io access. but usually read_all() don't have any future access.


The patch calls posix_fadvise *before* the main part of read_all.
Doesn't it make sense?

Quoted from the manpage of POSIX_FADVISE(2):

> Under Linux, POSIX_FADV_NORMAL sets the readahead window to
> the default size for the backing device; POSIX_FADV_SEQUENTIAL
> doubles this size,

I don't wonder that the patch works well.  Actually I can
reproduce the speed up.


$ sudo sysctl -w vm.drop_caches=1
vm.drop_caches = 1

$ ./ruby.old t.rb
       user     system      total        real
   0.100000   1.150000   1.250000 (  3.776475)

$ sudo sysctl -w vm.drop_caches=1
vm.drop_caches = 1

$ ./ruby.new t.rb
       user     system      total        real
   0.090000   0.750000   0.840000 (  3.766539)

$ uname -a
Linux inch 3.0.0-16-generic-pae #28-Ubuntu SMP Fri Jan 27 19:24:01 UTC 2012 i686 i686 i386 GNU/Linux

-- 
Yusuke Endoh <[e-mail]>
----------------------------------------
Feature #5995: calling io_advise_internal() in read_all()
https://bugs.ruby-lang.org/issues/5995

Author: Masaki Matsushita
Status: Assigned
Priority: Normal
Assignee: Motohiro KOSAKI
Category: core
Target version: 


=begin
I propose to call io_advise_internal() in read_all().
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'
 
 Benchmark.bm do |x|
   x.report do
     f = File.open("dummy") # dummy file(about 100MB )
     f.read
   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):

r34462:

 user     system      total        real
   0.050000   0.220000   0.270000 (  0.356033)
 
       user     system      total        real
   0.050000   0.190000   0.240000 (  0.332243)

       user     system      total        real
   0.060000   0.210000   0.270000 (  0.347758)

patched ruby:

 user     system      total        real
   0.030000   0.130000   0.160000 (  0.225866)

       user     system      total        real
   0.040000   0.170000   0.210000 (  0.250172)

       user     system      total        real
   0.040000   0.150000   0.190000 (  0.254654)

It shows the patch increases performance.
=end


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