linux-kernel - Re: Fwd: perf: callchain feature on ARM

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Message-ID: <20130830114903.GC1023@krava.brq.redhat.com>
Date:	Fri, 30 Aug 2013 13:49:03 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Jean Pihet <jean.pihet@...aro.org>
Cc:	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Fwd: perf: callchain feature on ARM - question about libunwind
 API

On Thu, Aug 29, 2013 at 07:15:00PM +0200, Jean Pihet wrote:

SNIP

> 
> The problem is that it is slow as hell (couple of minutes to report
> the callchain from a simple test app ;-|). I will look at the sampling
> rate and the caching next.

FYI there's elfutils alternative grewing now via libdw providing
API to do the 'remote unwind' as in libunwind. I'm not completely
sure, but I think it should support both .eh_frames and .debug_frames.

check:
git://git.fedorahosted.org/git/elfutils.git branch jankratochvil/unwindx86

the 'tests/backtrace-data.c' should be an example of what we want in perf

somewhere I should have perf changes to support this in
early version which no longer relevant.. but I recall it
was substantially faster due to some libdw inner caching

it's on my long term TODO list, so any help is welcome! ;-)

jirka
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