linux-kernel - Re: [PATCH v2] perf: libdw support for powerpc [ping]

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Date:   Tue, 20 Jun 2017 22:06:35 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Mark Wielaard <mark@...mp.org>
Cc:     Milian Wolff <milian.wolff@...b.com>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] perf: libdw support for powerpc [ping]

Em Thu, Jun 15, 2017 at 01:16:32PM +0200, Mark Wielaard escreveu:
> On Thu, 2017-06-15 at 10:46 +0200, Milian Wolff wrote:
> > Just a quick question: Have you guys applied my recent patch:
> > 
> > commit 5ea0416f51cc93436bbe497c62ab49fd9cb245b6
> > Author: Milian Wolff <milian.wolff@...b.com>
> > Date:   Thu Jun 1 23:00:21 2017 +0200
> > 
> >     perf report: Include partial stacks unwound with libdw
> >     
> >     So far the whole stack was thrown away when any error occurred before
> >     the maximum stack depth was unwound. This is actually a very common
> >     scenario though. The stacks that got unwound so far are still
> >     interesting. This removes a large chunk of differences when comparing
> >     perf script output for libunwind and libdw perf unwinding.
> > 
> > If not, then this could explain the issue you are seeing.
> 
> Thanks! No, I didn't have that patch (*) yet. It makes a huge
> difference. With that, Paolo's patch and the elfutils libdw powerpc64
> fallback unwinder patch, it looks like I get user stack traces for
> everything now on ppc64le.

Can I take that as a Tested-by: you?

- Arnaldo
 
> Cheers,
> 
> Mark
> 
> (*) It just this one-liner, but what a difference that makes:
> 
> --- a/tools/perf/util/unwind-libdw.c
> +++ b/tools/perf/util/unwind-libdw.c
> @@ -224,7 +224,7 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
>  
>         err = dwfl_getthread_frames(ui->dwfl, thread->tid, frame_callback, ui);
>  
> -       if (err && !ui->max_stack)
> +       if (err && ui->max_stack != max_stack)
>                 err = 0;
>  
>         /*