Mail Archives: djgpp/2001/04/08/19:00:30
Eli Zaretskii wrote:
>
> > From: Dennis Yelle <dennis51 AT jps DOT net>
> > Newsgroups: comp.os.msdos.djgpp
> > Date: Sun, 08 Apr 2001 12:18:42 -0700
> >
> > I ran the program, like this:
> > test > z
> > It finished in less than 1 second.
> >
> > I ran gdb like this:
> > gdb test.exe
> > break main
run
> > n
> > n
> > n
> > n
> > n
> > n
> > n
> > At this point, the program produces about 64 lines of
> > output to the screen, but I noticed a significant pause
> > every 4th line.
> > The total of all of the pauses was far more than 1 second.
> > So, it seems to me that the program is running significantly slower
> > under gdb than when run alone.
>
> No, GDB doesn't slow down programs, unless the program does something
> very special, such as issues a lot of DPMI function calls, or
> generates lots of SIGFPE exceptions.
>
> Normal programs don't do that. But your program, especially its car5
> function, allocates lots of memory in very small chunks (because it
> creates lots of temporary Bset objects), which forces the library to
> requests lots of small allocations from the DPMI server. Each such
> allocation gets caught by GDB, because it needs to be aware of all
> memory allocated by the program being debugged, to be able to
> deallocate that memory if the program is restarted without exiting the
> debugger. This causes a huge overhead, which is why you see this
> terrible slowdown.
Thank you very much for taking a look at this problem.
I modified the program to print only 18 lines,
and to call car6() instead of car5().
car6 is now this:
-------------------------------------
void car6()
{
int count = 0;
for( int i=0; i<10; i++) {
cout << "car6, i=" << i << '\n';
unsigned long ii = i;
for( int j=0; j<100; j++) {
unsigned long jj = j | ii;
for( int k=0; k<100; k++) {
unsigned long kk = jj | k;
for( int m=0; m<100; m++) {
unsigned long mm = kk | m;
if ( mm == 127)
if ( ++count < 5)
cout << "car6: " << ((i*100+j)*100+k)*100+m << '\n';
}
}
}
}
}
--------------------------------------
As you can see, the only memory allocation is a few
ints and a few unsigned longs on the stack, and possibly
in the calls to cout, but there are only 14 of those.
I don't think that gdb should be intercepting these more
than once, do you?
There terrible slow down is still there, in car6,
which takes much more than 10 times as long to run under
gdb as when run directly from the command line.
The new file is at
http://www2.jps.net/~vert/test6.cpp
the input file is still at
http://www2.jps.net/~vert/in
and it still takes less than 1 second to run from
the command line like this:
test
and much more than 20 times as long to run this way
gdb test.exe
break main
run
n
n
n
n
n
n
Thanks to anyone who reproduces this problem or
figures out exactly what is going on here and
how to fix it.
Dennis Yelle
--
I am a computer programmer and I am looking for a job.
There is a link to my resume here:
http://table.jps.net/~vert/
- Raw text -