Messages in this thread | | | Date | Mon, 25 Apr 2011 20:05:28 +0200 | From | Ingo Molnar <> | Subject | Re: [generalized cache events] Re: [PATCH 1/1] perf tools: Add missing user space support for config1/config2 |
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* 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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