Re: [PATCH 13/14] perf tools: warn on high overhead

[Andi Kleen]

kan.liang@xxxxxxxxx writes:

> From: Kan Liang <kan.liang@xxxxxxxxx>
>
> The rough overhead rate can be caculated by the sum of all kinds of
> overhead / elapsed time.
> If the overhead rate is higher than 10%, warning the user.

Thinking about this more: this is comparing the cost of a single
CPU to the total wall clock time. This isn't very good and can
give confusing results with many cores.

Perhaps we need two separate metrics here:

- cost of perf record on its CPU (or later on if it gets multi threaded
  more multiple). Warn if this is >50% or so.
- average perf collection overhead on a CPU. The 10% threshold here
  seems appropiate.

-Andi