Re: [GDB 7.6/GCC 4.8.0] Slowdown in GDB macro processing for cores?

Paul Smith
2013-05-22T18:50:34Z

On Fri, 2013-05-17 at 11:15 +0100, Pedro Alves wrote:
> > Against a core file it takes a second or longer per iteration of this
> > loop! FWIW, the class this macro operates on is very large and contains
> > a lot of data per object.
> >
> > Any ideas? Is there a handy way to tell where the slowdown is happening
> > here?
>
> I'm really surprised. If anything, I'd expect cores to be marginally faster.
> I suggest git bisecting gdb looking. Maybe you'll find the culprit
> easily that way.

Sorry for the delay. Getting a repro case was harder than it seemed
initially... just running "kill -9" on the process wasn't enough, or
didn't crash at the right spot, or something. We had to induce a
failure through a particular assert().

However, now I have a core file and executable built with my local copy
of GDB 4.8.0. If I run the macro using a locally-built copy of GDB
7.5.1, then I get this behavior:

$ time gdb-7.5.1 -c core.30095 -x macros.gdb myprog \
-ex "frame 4" -ex "ptracelog master->traceLog" -ex "q"
...prints 200 trace log lines...
real 0m2.811s
user 0m2.768s
sys 0m0.028s

so that's good stuff.

Now I try it with GDB 7.6, compiled locally using the identical
configure/etc. commands, and I get this behavior:

$ time gdb-7.6 -c core.30095 -x macros.gdb myprog \
-ex "frame 4" -ex "ptracelog master->traceLog" -ex "q"
...prints 200 trace log lines...
real 11m51.113s
user 11m46.324s
sys 0m2.168s

That's... not as good :-p.

I've just got this case working now, so I'll look into what's going on
here more.