linux-kernel - Re: [PATCH 4/4] perf trace: Add option to specify machine type

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Message-ID: <20131205144906.GD10333@ghostprotocols.net>
Date:	Thu, 5 Dec 2013 11:49:06 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 4/4] perf trace: Add option to specify machine type

Em Thu, Dec 05, 2013 at 07:33:20AM -0700, David Ahern escreveu:
> On 12/5/13, 6:50 AM, Arnaldo Carvalho de Melo wrote:
> >Em Wed, Dec 04, 2013 at 07:41:42PM -0700, David Ahern escreveu:
> >>Perhaps there is a better way to do this; I could not think of one and
> >>I don't see any field in the tracepoint that can be leveraged. So ...
> >>
> >>perf-trace autodetects the machine type (e.g., i386, x86_64, etc) via
> >>libaudit.
> >
> >And that means that using perf.data files from another machine, say,
> >ARM, will produce completely bogus results :-\
> 
> Indeed all offline analysis of trace data is wrong because it uses
> the arch of the machine running perf. I am not hitting that problem,
> but analysis on box.
> 
> >
> >We need a way to store this info in the perf.data header, i.e. use the
> >same algorithm that libaudit uses in audit_detect_machine() (and set the
> >open_id as well, btw) at 'perf record' time and store it somewhere.
> >
> >What we have now that could be used?
> >
> >Lets see:
> >
> >[acme@zoo linux]$ perf report | grep 'arch'
> ># arch : x86_64
> >[acme@zoo linux]$
> >
> >Would that be enough? Stephane?
> 
> That fixes one part -- using the arch in the file to translate
> system calls in the file.
> 
> But it is a per process problem: Some are 32-bit; others are 64-bit.
> I was hoping there was some option at the syscall entry level to tag
> the bitness. And then there is the problem of needing a solution

We need to look at how compat syscalls work and how that translates to
our raw_syscalls tracing needs :-\

> that works from RHEL6 forward. This patch at least allows me to have
> sensible data until something more clever is thought of.
> 
> David
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