libstdc++/10672: Binary IO with fstream is slow in 3.2+ compared to gcc 2.96

[daniel.lemire@nrc.gc.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: