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SubjectRe: [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 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 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.


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