[PATCH] D59539: [llvm-exegesis] Option to lobotomize dbscan (PR40880)

[Clement Courbet via Phabricator via llvm-commits]

courbet added a comment.

In D59539#1438165 <https://reviews.llvm.org/D59539#1438165>, @lebedev.ri wrote:

> In D59539#1436216 <https://reviews.llvm.org/D59539#1436216>, @lebedev.ri wrote:
>
> >
>
>
> I'm not saying that this *is* The solution, but i do believe the problem exists,
>  and i'm not sure what other approaches are there to solve it..
>
> There is another bug there, i suppose, we really should sort the measurements we loaded.


Sorting for clustering only works in one dimension. As soon as you have several dimensions (e.g. uops), it becomes more complex (hence dbscan & others).

> E.g. because now given measurement `0.5`, `1.0`, `1.5`, if they are in that order then
>  you get (i think, didn't check) two clusters: `0.5`+`1.0` and `1.5` (correct).
>  But if they are ``1.0`, 0.5`, `1.5`, then that will be a single cluster..

dbscan without lobotomization is mostly insensitive to point ordering (see https://reviews.llvm.org/D59693)


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