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[Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is e
From: |
Rik |
Subject: |
[Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow |
Date: |
Fri, 20 Jul 2018 13:26:50 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/61.0 |
Update of bug #54100 (project octave):
Status: None => Confirmed
Release: 4.4.0 => dev
Operating System: Microsoft Windows => Any
_______________________________________________________
Follow-up Comment #10:
I took the first of the most obvious suggestions, calculating the size of the
file just once and storing eof_pos in a variable. This produces a 2.5X
speed-up, and no regressions during testing, so I committed that change here
(https://hg.savannah.gnu.org/hgweb/octave/rev/336267b16a3d).
Test results were
-------------------------------------------------------------------------
Before
-------------------------------------------------------------------------
octave:18> tic; xt = fread (fid, [1000, 60], 'single', 0); toc
Elapsed time is 0.00138497 seconds.
octave:21> tic; xt = fread (fid, [1000, 60], 'single', 4); toc
Elapsed time is 0.252382 seconds.
-------------------------------------------------------------------------
After
-------------------------------------------------------------------------
octave:27> tic; xt = fread (fid, [1000, 60], 'single'); toc
Elapsed time is 0.00123215 seconds.
octave:34> tic; xt = fread (fid, [1000, 60], 'single', 4); toc
Elapsed time is 0.110174 seconds.
It is still the case that turning on 'skip' is approximately 100X slower
(0.110 vs. .0012). Maybe the next low-hanging optimization would be to just
read SKIP bytes from 'is' and discard them rather than using fseek itself. It
would require benchmarking.
_______________________________________________________
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- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow,
Rik <=
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Dan Sebald, 2018/07/20
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Rik, 2018/07/22
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Rik, 2018/07/23
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Dan Sebald, 2018/07/23
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Dan Sebald, 2018/07/23
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Rik, 2018/07/23
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Dan Sebald, 2018/07/24
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Rik, 2018/07/24
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Dan Sebald, 2018/07/29
- [Octave-bug-tracker] [bug #54100] fread using SKIP larger than zero is extremely slow, Rik, 2018/07/29