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SubjectRe: [generalized cache events] Re: [PATCH 1/1] perf tools: Add missing user space support for config1/config2

* Dehao Chen <danielcdh@gmail.com> wrote:

> > ... and the resulting low level of noise in the average period length is
> > what matters. The instruction itself will still be one of the hotspot
> > instructions, statistically.
>
> Not true. This skid will lead to some aggregation and shadow effects on some
> certain instructions. To make things worse, these effects are deterministic
> and cannot be removed by either sampling for multiple times or by averaging
> among instructions within a basic block. As a result, some actual "hot spot"
> are not sampled at all. You can simply try to collect a basic block level
> CPI, and you'll get a very misleading profile.

This certainly does not match the results i'm seeing on real applications,
using "-e instructions:pp" PEBS+LBR profiling. How do you explain that? Also,
can you demonstrate your claim with a real example?

Thanks,

Ingo


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