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

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On Sat, 16 May 2015 11:41:09 -0700 (PDT)
Malcolm McLean <malcolm.mclean5@btinternet.com> wrote:

> On Saturday, May 16, 2015 at 3:57:16 PM UTC+1, Lew Pitcher wrote:
> > 
> > If I read that fread() call correctly, you are (atomically) reading
> > the file one byte at a time, for as many bytes as will fit in your
> > buffer. That's gotta be expensive.
> > 
> He's got 13GB or so to read.
> The operation is taking 15 minutes. But the computer runs at 2.4Ghz.
> So if I'm doing my calculations correctly, each byte is taking 166
> operations to read. That seems way too high, even if there's a
> function call for each one.

I have experienced extremely slow memory initialization on first pass
when disk cache occupies most of ram. Say it's about 20-200 times slower
then on second initialization pass. Say it could take around minute to
initialize chunk of 800mb on my machine.
This issue seems fixed in latest kernel 4.0.3

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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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