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

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Date:	Thu, 05 Dec 2013 07:33:20 -0700
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
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

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 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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