Re: [PATCH V2 22/23] perf tools: Allow system-wide events to keep their own CPUs

[Adrian Hunter <adrian.hunter@intel.com>]

On 12/05/22 08:27, Namhyung Kim wrote:
> On Fri, May 6, 2022 at 5:27 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> Currently, user_requested_cpus supplants system-wide CPUs when the evlist
>> has_user_cpus. Change that so that system-wide events retain their own
>> CPUs and they are added to all_cpus.
>>
>> Acked-by: Ian Rogers <irogers@google.com>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>> ---
>>  tools/lib/perf/evlist.c | 11 +++++------
>>  1 file changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
>> index 1c801f8da44f..9a6801b53274 100644
>> --- a/tools/lib/perf/evlist.c
>> +++ b/tools/lib/perf/evlist.c
>> @@ -40,12 +40,11 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
>>          * We already have cpus for evsel (via PMU sysfs) so
>>          * keep it, if there's no target cpu list defined.
>>          */
>> -       if (!evsel->own_cpus || evlist->has_user_cpus) {
>> -               perf_cpu_map__put(evsel->cpus);
>> -               evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
>> -       } else if (!evsel->system_wide &&
>> -                  !evsel->requires_cpu &&
>> -                  perf_cpu_map__empty(evlist->user_requested_cpus)) {
>> +       if (!evsel->own_cpus ||
>> +           (!evsel->system_wide && evlist->has_user_cpus) ||
>> +           (!evsel->system_wide &&
>> +            !evsel->requires_cpu &&
>> +            perf_cpu_map__empty(evlist->user_requested_cpus))) {
> 
> This is getting hard to understand.  IIUC this propagation basically
> sets user requested cpus to evsel unless it has its own cpus, right?

I put the conditional logic altogether because that is kernel style but
it does make it practically unreadable.

If we start with the original logic:

	if (!evsel->own_cpus || evlist->has_user_cpus) {
		perf_cpu_map__put(evsel->cpus);
		evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
	} else if (!evsel->system_wide && perf_cpu_map__empty(evlist->user_requested_cpus)) {
		perf_cpu_map__put(evsel->cpus);
		evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
	} else if (evsel->cpus != evsel->own_cpus) {
		perf_cpu_map__put(evsel->cpus);
		evsel->cpus = perf_cpu_map__get(evsel->own_cpus);
	}

Then make it more readable, i.e. same functionality

	struct perf_cpu_map *cpus;

	if (!evsel->own_cpus || evlist->has_user_cpus)
		cpus = evlist->user_requested_cpus;
	else if (!evsel->system_wide && perf_cpu_map__empty(evlist->user_requested_cpus))
		cpus = evlist->user_requested_cpus;
	else
		cpus = evsel->own_cpus;

	if (evsel->cpus != cpus) {
		perf_cpu_map__put(evsel->cpus);
		evsel->cpus = perf_cpu_map__get(cpus);
	}

Then separate out the conditions, i.e. still same functionality

	if (!evsel->own_cpus)
		cpus = evlist->user_requested_cpus;
	else if (evlist->has_user_cpus)
		cpus = evlist->user_requested_cpus;
	else if (evsel->system_wide)
		cpus = evsel->own_cpus;
	else if (perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
		cpus = evlist->user_requested_cpus;
	else
		cpus = evsel->own_cpus;

Then add the new requires_cpu flag:

	if (!evsel->own_cpus)
		cpus = evlist->user_requested_cpus;
	else if (evlist->has_user_cpus)
		cpus = evlist->user_requested_cpus;
	else if (evsel->system_wide)
		cpus = evsel->own_cpus;
-	else if (perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
+	else if (!evsel->requres_cpu && perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
		cpus = evlist->user_requested_cpus;
	else
		cpus = evsel->own_cpus;

Then make system_wide keep own_cpus even if has_user_cpus:

	if (!evsel->own_cpus)
		cpus = evlist->user_requested_cpus;
+	else if (evsel->system_wide)
+		cpus = evsel->own_cpus;
	else if (evlist->has_user_cpus)
		cpus = evlist->user_requested_cpus;
-	else if (evsel->system_wide)
-		cpus = evsel->own_cpus;
	else if (!evsel->requres_cpu && perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
		cpus = evlist->user_requested_cpus;
	else
		cpus = evsel->own_cpus;

Which leaves:

	if (!evsel->own_cpus)
		cpus = evlist->user_requested_cpus;
	else if (evsel->system_wide)
		cpus = evsel->own_cpus;
	else if (evlist->has_user_cpus)
		cpus = evlist->user_requested_cpus;
	else if (!evsel->requres_cpu && perf_cpu_map__empty(evlist->user_requested_cpus)) /* per-thread */
		cpus = evlist->user_requested_cpus;
	else
		cpus = evsel->own_cpus;

And putting it back together:

	if (!evsel->own_cpus ||
	    (!evsel->system_wide && evlist->has_user_cpus) ||
	    (!evsel->system_wide &&
	     !evsel->requires_cpu &&
	     perf_cpu_map__empty(evlist->user_requested_cpus))) {
		cpus = evlist->user_requested_cpus;
	else
		cpus = evsel->own_cpus;

Perhaps I shouldn't put it together?

> 
> But the hybrid pmus make this complex.  Maybe we can move the
> logic in evlist__fix_hybrid_cpus() here and simplify it like below
> 
> if (evsel->own_cpus) {
>    if (evsel->pmu->is_hybrid)
>       evsel->cpus = fixup_hybrid_cpus(evsel>own_cpus,
>                                       evlist->user_requested_cpus);  //?
>    else
>       evsel->cpus = evlist->own_cpus;  // put + get
> } else {
>    evsel->cpus = evlist->user_requested_cpus;  // put + get
> }
> 
> Then we need to make sure evsel->pmu is set properly.
> 
> What do you think?

Hybrid handling looks complicated.  I would have to spend time
better understanding it.

So, in the context of this patch set, I don't want to look at
issues with hybrid CPUs, except that there should be no change
to how they are handled.

> 
> Thanks,
> Namhyung
> 
> 
>>                 perf_cpu_map__put(evsel->cpus);
>>                 evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
>>         } else if (evsel->cpus != evsel->own_cpus) {
>> --
>> 2.25.1
>>