Messages in this thread | | | Date | Wed, 27 May 2015 10:46:26 +0200 | From | Martin Liška <> | Subject | Re: [RFC] Add --show-total-period for perf annotate |
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On 05/26/2015 07:03 PM, Andi Kleen wrote: >> Anyway, attached patch is capable of displaying milliseconds approximation for each instruction. > > You realize that the events perf is not counting do not directly map to > wall time? Even if you count cycles, the cycles are either stopping in idle > or changing unit as the CPU's frequencies change. For other events the > relationship is even more remote, think what happens when counting cache or > TLB misses. > > Also even if it was mapping to time somehow, it's just a hit, not a > duration, so it cannot say how long a individual instruction took. > > So you cannot map a sample event to time. > > To do what you want you would need to use something like processor > trace, which can do exact accounting. > > I think the only thing that makes sense is to account it relative to > the event counts. > > -Andi >
Hello Andi.
I realize all aspects and capabilities of perf infrastructure. Even though these numbers are not precise, I helped me a lot with debugging of a benchmark which heavily utilizes a single CPU and runs in magnitude of seconds.
Ok, so let's convert the patch to feature that we can map an instruction to a percentage number of events (cycles) it takes.
If I understand correctly, is it just about division of the number of events related to an instruction and total number of events?
Thanks, Martin
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