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

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Message-ID: <1497525392.3755.307.camel@klomp.org>
Date:   Thu, 15 Jun 2017 13:16:32 +0200
From:   Mark Wielaard <mark@...mp.org>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org, acme@...nel.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]

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.

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;
 
        /*