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

[Ingo Molnar]

* Dehao Chen <danielcdh@xxxxxxxxx> 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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