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Re: [GDB 7.6/GCC 4.8.0] Slowdown in GDB macro processing for cores?
- From: Pedro Alves <palves at redhat dot com>
- To: psmith at gnu dot org
- Cc: gdb at sourceware dot org
- Date: Fri, 17 May 2013 11:15:05 +0100
- Subject: Re: [GDB 7.6/GCC 4.8.0] Slowdown in GDB macro processing for cores?
- References: <1368733335 dot 4101 dot 743 dot camel at pdsdesk>
On 05/16/2013 08:42 PM, Paul Smith wrote:
> Hi all. Is anyone aware of an issue with a big slowdown running macros
> on core files? I'm not sure if this is related to GCC 4.8 or GDB 7.6,
> or what, but I'm seeing a 4x or more slowdown when running macros on
> core files from previous releases.
> Running against a live process is the same speed as before.
If you haven't yet, it'd make sense to try process vs core at the
exact same spot:
$ gdb myprogram
(gdb) gcore mycore
$ gdb myprogram -c mycore
> 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
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.
> Should we just drop back to DWARF2 or DWARF3 (I haven't checked
> if that will help tho)?
Ideally no, of course. Let us know if that indeed helps.
Using DWARF < 4 should make it easier to git bisect the
culprit, as you can then start bisecting before the
patches that added support for DWARF4.