Re: [Patch v5 0/6] Bug fixes on topdown events reordering

[Ian Rogers]

On Tue, Oct 1, 2024 at 2:02 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Fri, 13 Sep 2024 08:47:06 +0000, Dapeng Mi wrote:
>
> > Changes:
> > v5 -> v6:
> >   * no function change.
> >   * rebase patchset to latest code of perf-tool-next tree.
> >   * Add Kan's reviewed-by tag.
> >
> > History:
> >   v4: https://lore.kernel.org/all/20240816122938.32228-1-dapeng1.mi@xxxxxxxxxxxxxxx/
> >   v3: https://lore.kernel.org/all/20240712170339.185824-1-dapeng1.mi@xxxxxxxxxxxxxxx/
> >   v2: https://lore.kernel.org/all/20240708144204.839486-1-dapeng1.mi@xxxxxxxxxxxxxxx/
> >   v1: https://lore.kernel.org/all/20240702224037.343958-1-dapeng1.mi@xxxxxxxxxxxxxxx/
> >
> > [...]
>
> Applied to perf-tools-next, thanks!

I disagreed with an early patch set and the issue wasn't resolved. Specifically:

https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/commit/?h=perf-tools-next&id=3b5edc0421e2598a0ae7f0adcd592017f37e3cdf
```
  /* Followed by topdown events. */
  if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs))
  return -1;
- if (!arch_is_topdown_metrics(lhs) && arch_is_topdown_metrics(rhs))
+ /*
+ * Move topdown events forward only when topdown events
+ * are not in same group with previous event.
+ */
+ if (!arch_is_topdown_metrics(lhs) && arch_is_topdown_metrics(rhs) &&
+     lhs->core.leader != rhs->core.leader)
  return 1;
```
Is a broken comparator as the lhs then rhs behavior varies from the
rhs then lhs behavior. The qsort implementation can randomly order the
events.
Please drop/revert.

Thanks,
Ian

> Best regards,
> Namhyung