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

Liang, Kan
2024-10-03T19:45:14Z

On 2024-10-03 12:45 p.m., Namhyung Kim wrote:
>>> If the algorithms cannot be changed, can you please give some
>>> suggestions, especially for the sample read failure?
>> So this is symmetric:
>> ```
>> if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs))
>> return -1;
>> if (!arch_is_topdown_metrics(lhs) && arch_is_topdown_metrics(rhs))
>> return 1;
>> ```
>> That is were lhs and rhs swapped then you'd get the expected comparison order.
>> ```
>> if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs) &&
>> lhs->core.leader != rhs->core.leader)
>> return -1;
>> if (!arch_is_topdown_metrics(lhs) && arch_is_topdown_metrics(rhs) &&
>> lhs->core.leader != rhs->core.leader)
>> return 1;
>> ```
>> Is symmetric as well.
>> ```
>> if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs))
>> return -1;
>> if (!arch_is_topdown_metrics(lhs) && arch_is_topdown_metrics(rhs) &&
>> lhs->core.leader != rhs->core.leader)
>> return 1;
>> ```
>> (what this patch does) is not symmetric as the group leader impacts
>> the greater-than case but not the less-than case.
>>
>> It is not uncommon to see in a sort function:
>> ```
>> if (cmp(a, b) <= 0) {
>> assert(cmp(b,a) >= 0 && "check for unstable/broken compare functions");
>> ```
> I see. So are you proposing this?
>
> diff --git a/tools/perf/arch/x86/util/evlist.c b/tools/perf/arch/x86/util/evlist.c
> index 438e4639fa892304..46884fa17fe658a6 100644
> --- a/tools/perf/arch/x86/util/evlist.c
> +++ b/tools/perf/arch/x86/util/evlist.c
> @@ -70,7 +70,8 @@ int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs)
> if (arch_is_topdown_slots(rhs))
> return 1;
> /* Followed by topdown events. */
> - if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs))
> + if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs) &&
> + lhs->core.leader != rhs->core.leader)
> return -1;
> /*
> * Move topdown events forward only when topdown events
>
> Dapeng and Kan, can you verify if it's ok? My quick tests look ok.

I verified the above change. It works well.

Tested-by: Kan Liang <kan.liang@linux.intel.com>

Thanks,
Kan