Re: Two questions on perf dwarf callchains

[Mauro Andreolini <mauro.andreolini@gmail.com>]

Il giorno mer, 29/01/2014 alle 12.18 +0100, Jiri Olsa ha scritto:
> On Fri, Jan 17, 2014 at 11:21:23AM +0100, Mauro Andreolini wrote:
> > Hi all,
> 
> hi
> 
> > 
> > No kallsyms or vmlinux with build-id
4c6ab941f31dde04c2a481430218994849927c8d was found
> > [ext4] with build id 4c6ab941f31dde04c2a481430218994849927c8d not
found, continuing without symbols
> > No kallsyms or vmlinux with build-id
21f163b0a8a8b924efdd173b8f83ad723d378958 was found
> > [drm] with build id 21f163b0a8a8b924efdd173b8f83ad723d378958 not
found, continuing without symbols
> > No kallsyms or vmlinux with build-id
d0bd7dd69886c2dccde18dee760b6d39cc0b5a55 was found[qxl] with build id
d0bd7dd69886c2dccde18dee760b6d39cc0b5a55 not found, continuing without
symbols
> > No kallsyms or vmlinux with build-id
8d13e6f0c4d4f8b4628c8c4bd6c660b0a00576df was found[ttm] with build id
8d13e6f0c4d4f8b4628c8c4bd6c660b0a00576df not found, continuing without
symbols
> 
> hum, do you have kernel-debuginfo* packages installed?
Hi, thanks for your time. I am using Arch Linux, which does not provide
separate -debuginfo packages as Fedora. However, I have compiled the
kernel with debug-info and with frame pointers. Now I am not seeing
those messages anymore. Sorry for that noise.

> 
> 
> SNIP
> 
> > 
> > Problem n.2: sometimes perf prints bogus callchains (in particular
> > when the various printf() variants are involved).
> > 
> >                  |--1.46%-- 0xffffffffa048a275
> >                  |          0xffffffffa048c110
> >                  |          0xffffffffa04909e7
> >                  |          |
> >                  |          |--80.00%-- 0xffffffffa0490afa
> >                  |          |          0xffffffffa048ee8b
> >                  |          |          0xffffffffa048ba8f
> >                  |          |          bit_bmove
> >                  |          |          fbcon_redraw_blit.isra.22
> >                  |          |          fbcon_scroll
> >                  |          |          scrup
> >                  |          |          lf
> >                  |          |          do_con_trol
> >                  |          |          do_con_write.part.18
> >                  |          |          con_write
> >                  |          |          do_output_char
> >                  |          |          n_tty_write
> >                  |          |          tty_write
> >                  |          |          vfs_write
> >                  |          |          sys_write
> >                  |          |          system_call_fastpath
> >                  |          |          __GI___libc_write
> >                  |          |          |
> >                  |          |          |--50.00%-- vfprintf
> >                  |          |          |          0x0
<---HERE
> >                  |          |          |
> >                  |          |          |--25.00%-- main
> >                  |          |          |          __libc_start_main
> >                  |          |          |          _start
> >                  |          |          |          0x0
<---HERE
> >                  |          |          |
> >                  |          |           --25.00%-- 0x7facc1df12a0
HERE
> 
> this one could be caused by:
> http://marc.info/?l=linux-kernel&m=134934717011451&w=2
> I never managed to push this change through.. need to revisit it ;-)
> 
> if you want to try, I rebased the patch and put it in here:
>   git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   branch perf/rsp_fix1
> 
>   commit:
>
https://git.kernel.org/cgit/linux/kernel/git/jolsa/perf.git/commit/?h=perf/rsp_fix1&id=5eed39431f9b1e65e740a2e3e197c79f0a1bcf6b
> 
> it still fixies some of the backtraces for me
Oh, thanks a lot. I will try this ASAP. Meanwhile, using the frame
pointer
for kernel, libraries and executables works like a charm.

Thanks for your time.
Mauro