Re: QEMU-KVM metrics collection | Calculation of instructions performed from perf events

[Andi Kleen <andi@firstfloor.org>]

Elena Talkova <e.talkova@zoho.eu> writes:
>
> I have 2 problems so far:
>
> 1) I'm not sure how to use all available events to calculate number of instructions performed (integer and floating-points)

You would need a better definition. There's no way
to count "all integer" instructions. Just all instructions,
or some specific classes of instructions.

If you need an exact instruction histogram the only
way is to use special instrumentation tools like pin.

> 2) I get totally different results when running perf for a process on
> host machine and for a virtual machine process (with VM values often
> being just zeros)

Measuring the counts from the host should work, except for
PEBS events.

> Sandy bridge:
>
> FP_COMP_OPS_EXE.SSE_SCALAR_SINGLE

These events are difficult to use because they include speculative and
re-issued execution, which can be high. Typically you need a significant
workload specific correction factor.

The retired Broadwell, Skylake events below don't have this problem. But it's
still not "all floating point" instructions, just all floating point
arithmetic.

-Andi