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libstdc++/10672: Binary IO with fstream is slow in 3.2+ compared to gcc 2.96
- From: daniel dot lemire at nrc dot gc dot ca
- To: gcc-gnats at gcc dot gnu dot org
- Date: 8 May 2003 00:45:57 -0000
- Subject: libstdc++/10672: Binary IO with fstream is slow in 3.2+ compared to gcc 2.96
- Reply-to: daniel dot lemire at nrc dot gc dot ca
>Number: 10672
>Category: libstdc++
>Synopsis: Binary IO with fstream is slow in 3.2+ compared to gcc 2.96
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Thu May 08 00:45:59 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator: daniel.lemire@nrc.gc.ca
>Release: gcc version 3.4 20030507 (experimental) + gcc version 3.2.3
>Organization:
>Environment:
linux 2.4.18-3 (RedHat 7.3) on 686
>Description:
fstream in 3.x series is extremely slow for binary
files compared to pre-3.x.
latest CVS (20030507)
real 0m4.773s
user 0m1.680s
sys 0m3.010s
3.2.3 (release)
real 0m5.503s
user 0m2.710s
sys 0m2.790s
gcc 2.96 (Clearly better)
real 0m2.920s
user 0m1.090s
sys 0m1.830s
Of course, this was one trial on the same machine.
I have more complex software here where the drop in
speed is as high as 5 times. This is a show stopper
for me.
(This is related to bug 8761 but this bug is specific
to binary files and thus doesn't involve formatting
issues.)
>How-To-Repeat:
given the file test.cpp below
===================
#include <fstream>
using namespace std;
int main() {
fstream s("test.bin",ios::binary | ios::in | ios::out);
for (int i = 0; i < 300000;i++) {
s.seekp(0);
s.write((char *) & i, sizeof(int));
s.seekp(sizeof(int));
s.write((char *) & i, sizeof(int));
}
return 0;
}
===============
do
g++ -o a.out test.cpp -O2
followed by
time ./a.out
>Fix:
Revert back to gcc 2.96.
>Release-Note:
>Audit-Trail:
>Unformatted: