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

Liang, Kan
2022-05-13T17:32:51Z

On 5/13/2022 12:42 PM, Namhyung Kim wrote:
> On Fri, May 13, 2022 at 9:11 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> On 13/05/22 18:46, Liang, Kan wrote:
>>>
>>>
>>> On 5/13/2022 11:21 AM, Adrian Hunter wrote:
>>>> On 13/05/22 17:12, Liang, Kan wrote:
>>>>>
>>>>>
>>>>> On 5/13/2022 12:48 AM, Adrian Hunter wrote:
>>>>>> On 12/05/22 21:53, Namhyung Kim wrote:
>>>>>>> On Thu, May 12, 2022 at 3:35 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>>>>>>
>>>>>>>> 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?
>>>>>>>
>>>>>>> Cool, thanks a lot for explaining it in detail.
>>>>>>> I do not oppose your change but little worried about the
>>>>>>> complexity. And I think we have some issues with uncore
>>>>>>> events already.
>>>>>>
>>>>>> Yes it is a bit complicated because we are handling
>>>>>> many different use cases.
>>>>>>
>>>>>>>
>>>>>>> So do you have any idea where evsel->own_cpus
>>>>>>> doesn't propagate to evsel->cpus?
>>>>>>
>>>>>> We let the user's list of CPUs override it i.e. the
>>>>>> evlist->has_user_cpus case. Essentially we are expecting
>>>>>> the user to know what they are doing.
>>>>>>
>>>>>>>
>>>>>>> I think evsel->system_wide and evsel->requires_cpu
>>>>>>> can be replaced to check evsel->own_cpus instead.
>>>>>>
>>>>>> Not at the moment because we let the user override
>>>>>> own_cpus.
>>>>>
>>>>> Do we check whether the user's input is valid (match the PMU's cpumask) before the override?
>>>>>
>>>>> I think we know the PMU name. The cpumask of the PMU can be found in the sysfs. So we should have enough information for a sanity check.
>>>>
>>>> For the uncore PMU case, I am not sure what sanity is :-)
>>>>
>>>
>>> For a non-core PMU, e.g., uncore, cstate, power and etc. The cpumask is under the /sys/devices/<PMU>/cpumask. It shows the cpumask which kernel supports. If a end user request a different CPU other that the cpumask, I think it's better throw a waning. It should mitigate the confusion which Namhyung mentioned (uncore -C1,2).
>>
>> So you couldn't get uncore events unless you are also coincidentally wanting to trace CPU 0.
>>
>> I guess really the requrement is not to perf_event_open() an uncore PMU more than once?
>> To figure that out we'd need to be able map CPUs to uncore PMUs?
>
> We might just use evsel->own_cpus for uncore events and
> if the user-given cpu list contains other cpus it can show an
> warning.
>

Yes, it sounds reasonable.

Thanks,
Kan