[llvm-dev] LNT server function perf profile comparison

Kristof Beyls via llvm-dev llvm-dev at lists.llvm.org
Fri Aug 9 00:50:13 PDT 2019

Hi Felix,

This is not really expected behaviour.
Are you getting "0" for all instructions, or only for some where you didn't
expect it?
Are you sure the function you show in the screenshot actually still gets
called in the transformed program?

FWIW and orthogonally - I'd recommend using the View: "Control-Flow Graph
(X86-64)". That way, you'll get counters aggregated per basic block, which
removes a bit some of the confusion that can result when perf associates
events with an instruction a number of instructions removed from the
instruction causing the event you were measuring.

Hoping this helps a little,


Op vr 9 aug. 2019 om 01:16 schreef Felix Berlakovich via llvm-dev <
llvm-dev at lists.llvm.org>:

> Hi!
> I have implemented a security feature in LLVM and now I want to evaluate
> the performance impact by comparing the perf profile of the originally
> compiled program and the modified program. For that I have run a benchmark
> with lnt runtest test-suite and –use-perf=all. I can compare the recorded
> counters in the lnt runserver webinterface perfectly fine with the side by
> side comparison. However, as soon as I switch from “Relative (%)” to
> “Absolute numbers”, one side of the comparison only displays 0 anymore. Is
> this normal behavior or is something with my lnt server / perf profiles
> broken?
> You can see a screenshot of how it looks like here: https://ibb.co/dDnZp5T
> Regards,
> Felix
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
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