On Mon, 22 Mar 2010, Marc Brünink wrote:
>
> short version: Is it in theory possible to get 100% accurate result for
> BR_INST_RETIRED:ANY?
which CPU type are you running this on?
> So: Is it possible to get a 100% accurate performance counter result (in
> theory) (for BR_INST_RETIRED:ANY)? Which are the factors distorting the
> results? Is it possible to get rid of them completely?
I think it's interrupts again, as with the retired_instruction case.
I ran some tests on a core2 machine using perf on a 2.6.32 core2 machine.
The test was my "ten_billion" micro-benchmark I was talking about on
Friday.
Performance counter stats for './ten_billion':
10000000514 instructions # 0.000 IPC
4999990511 branches
1 page-faults
1.675311657 seconds time elapsed
The expected number of branches for this code is 4,999,989,996. So
the overcount is 513, which is almost exactly the same as the extra count
on retired instructions, which makes it look like the retired branch count
is also being incremented once each time an interrupt happens.
Vince
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