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Re: Mysterious slow IO on fread() to large buffer on large Dell system

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On Fri, 15 May 2015 22:27:19 -0700
mathog <dmathog@gmail.com> wrote:

> glen herrmannsfeldt wrote:
> > You have to be careful with the timing.  Did you do the first one
> > first, and then the second one?
> >
> > On a system with many gigabytes of disk cache in memory?
> >
> > I suspect that the second was reading from disk cache, not actual
> > disk.
> 
> I did them both twice with the same results.  So not a read from disk 
> vs. read from cache issue.  It also isn't just one particular file
> that does this, it is any file, including just a pile of zero bytes
> made with dd.
> 
> Thanks
> 
Have you tried to read file chunk by chunk? I mean not to read whole
content at once, rather to read eg 4kb by 4kb and discard. Perhaps what
takes time is OS allocating large number of pages?

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Mysterious slow IO on fread() to large buffer on large Dell system mathog <dmathog@gmail.com> - 2015-05-15 18:45 -0700
  Re: Mysterious slow IO on fread() to large buffer on large Dell system Ian Collins <ian-news@hotmail.com> - 2015-05-16 14:09 +1200
  Re: Mysterious slow IO on fread() to large buffer on large Dell system Siri Cruz <chine.bleu@yahoo.com> - 2015-05-15 19:20 -0700
    Re: Mysterious slow IO on fread() to large buffer on large Dell system mathog <dmathog@gmail.com> - 2015-05-15 22:29 -0700
      Re: Mysterious slow IO on fread() to large buffer on large Dell system Siri Cruz <chine.bleu@yahoo.com> - 2015-05-16 08:47 -0700
    Re: Mysterious slow IO on fread() to large buffer on large Dell system Robert Wessel <robertwessel2@yahoo.com> - 2015-05-16 02:11 -0500
  Re: Mysterious slow IO on fread() to large buffer on large Dell system Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-05-15 19:23 -0700
  Re: Mysterious slow IO on fread() to large buffer on large Dell system glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-16 05:05 +0000
    Re: Mysterious slow IO on fread() to large buffer on large Dell system Melzzzzz <mel@zzzzz.com> - 2015-05-16 07:20 +0200
    Re: Mysterious slow IO on fread() to large buffer on large Dell system mathog <dmathog@gmail.com> - 2015-05-15 22:27 -0700
      Re: Mysterious slow IO on fread() to large buffer on large Dell system Melzzzzz <mel@zzzzz.com> - 2015-05-16 07:59 +0200
      Re: Mysterious slow IO on fread() to large buffer on large Dell system Ian Collins <ian-news@hotmail.com> - 2015-05-16 18:31 +1200
  Re: Mysterious slow IO on fread() to large buffer on large Dell system Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-05-16 10:57 -0400
    Re: Mysterious slow IO on fread() to large buffer on large Dell system Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-05-16 10:51 -0600
    Re: Mysterious slow IO on fread() to large buffer on large Dell system Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-05-16 11:41 -0700
      Re: Mysterious slow IO on fread() to large buffer on large Dell system Melzzzzz <mel@zzzzz.com> - 2015-05-16 21:01 +0200
        Re: Mysterious slow IO on fread() to large buffer on large Dell system glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-16 19:37 +0000
          Re: Mysterious slow IO on fread() to large buffer on large Dell system Noob <root@127.0.0.1> - 2015-05-16 22:14 +0200
    Re: Mysterious slow IO on fread() to large buffer on large Dell system gamo <gamo@telecable.es> - 2015-05-17 12:36 +0200
  Re: Mysterious slow IO on fread() to large buffer on large Dell system Paul <nospam@needed.com> - 2015-05-16 11:29 -0400
  Re: Mysterious slow IO on fread() to large buffer on large Dell system mathog <dmathog@gmail.com> - 2015-05-16 10:50 -0700
    Re: Mysterious slow IO on fread() to large buffer on large Dell system Johann Klammer <klammerj@NOSPAM.a1.net> - 2015-05-17 01:43 +0200
  Re: Mysterious slow IO on fread() to large buffer on large Dell system Stephen Sprunk <stephen@sprunk.org> - 2015-05-16 16:40 -0500
  Re: Mysterious slow IO on fread() to large buffer on large Dell system mathog <dmathog@gmail.com> - 2015-05-26 09:58 -0700

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