Re: [PATCH v2] perf evlist: Fix 'perf record -C xx' failed issue

[Chunxin Zang]

> On Mar 20, 2024, at 04:33, Ian Rogers <irogers@xxxxxxxxxx> wrote:
> 
> On Tue, Mar 19, 2024 at 2:14 AM Chunxin Zang <spring.cxz@xxxxxxxxx> wrote:
>> 
>> The cpu has 8 performance-cores and 8 efficient-cores on my pc.
>> 0-15 are performance-cores
>> 16-23 are 8 efficient-cores
>> 
>> When I run "perf record -C xxx", the command fails if xxx all belong to
>> performance cores or efficient cores
>> 
>> The results are as follows
>> 
>>  # perf record -C 12
>>  WARNING: A requested CPU in '12' is not supported by PMU 'cpu_atom' (CPUs 16-23) for event 'cycles:P'
>>  Error:
>>  The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cpu_atom/cycles:P/).
>>  /bin/dmesg | grep -i perf may provide additional information.
>> 
>>  # perf record -C 14-17
>>  WARNING: A requested CPU in '14-17' is not supported by PMU 'cpu_atom' (CPUs 16-23) for event 'cycles:P'
>>  WARNING: A requested CPU in '14-17' is not supported by PMU 'cpu_core' (CPUs 0-15) for event 'cycles:P'
>>  ^C[ perf record: Woken up 1 times to write data ]
>> 
>> The reason is that the cpu_map of 'cpu_atom'-evsel is empty, causing
>> the sys_perf_event_open() result to fail.
>> 
>> Changes in v2:
>> - fix memory leak about 'intersect'
>> 
>> Signed-off-by: Chunxin Zang <spring.cxz@xxxxxxxxx>
>> Reviewed-by: Chen Yang <yangchen11@xxxxxxxxxxx>
>> ---
>> tools/perf/util/evlist.c | 24 +++++++++++++++++-------
>> 1 file changed, 17 insertions(+), 7 deletions(-)
>> 
>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>> index 55a300a0977b..babbde29341f 100644
>> --- a/tools/perf/util/evlist.c
>> +++ b/tools/perf/util/evlist.c
>> @@ -2499,7 +2499,7 @@ void evlist__check_mem_load_aux(struct evlist *evlist)
>> void evlist__warn_user_requested_cpus(struct evlist *evlist, const char *cpu_list)
>> {
>>        struct perf_cpu_map *user_requested_cpus;
>> -       struct evsel *pos;
>> +       struct evsel *pos, *tmp;
>> 
>>        if (!cpu_list)
>>                return;
>> @@ -2508,18 +2508,28 @@ void evlist__warn_user_requested_cpus(struct evlist *evlist, const char *cpu_lis
>>        if (!user_requested_cpus)
>>                return;
>> 
>> -       evlist__for_each_entry(evlist, pos) {
>> +       evlist__for_each_entry_safe(evlist, tmp, pos) {
>>                struct perf_cpu_map *intersect, *to_test;
>>                const struct perf_pmu *pmu = evsel__find_pmu(pos);
>> 
>>                to_test = pmu && pmu->is_core ? pmu->cpus : cpu_map__online();
> 
> Perhaps this would be clearer if we just made sure requested uncore
> CPUs were online. Uncore cpu maps are weird, they say the default CPU
> but other CPUs are valid. It'd be worth testing the impact of this
> change on uncore events.

Hi  Ian,

I tested the "uncore_clock" event and it seems to work fine.
The results are as follows:

   $ ~/perf stat  -e uncore_clock/clockticks/  -C 12


    ^C
     Performance counter stats for 'CPU(s) 12':

           740,036,624      uncore_clock/clockticks/

           4.135909502 seconds time elapsed

> 
>>                intersect = perf_cpu_map__intersect(to_test, user_requested_cpus);
>> -               if (!perf_cpu_map__equal(intersect, user_requested_cpus)) {
>> -                       char buf[128];
>> +               if (!intersect) {
>> +                       evlist__remove(evlist, pos);
>> +                       evsel__delete(pos);
>> +                       perf_cpu_map__put(intersect);
> 
> evlist__warn_user_requested_cpus seems like a wrong function name if
> evsels are being removed. Perhaps something like
> evlist__remove_empty_cpu_map_evsels. It seems this change will remove
> warnings in cases like:
> 
> $ perf record cpu_atom/cycles/ -C 0 ...
> 
Yes ,I will fix it.

> I wonder that we need a flag in the evsel to say when an event comes
> from wildcard expansion so we only don't warn/remove in that case.
> 
That sounds very reasonable. Furthermore, if the event is not from wildcard and it's 
cpu maps is empty, the evsel needs to be deleted and the process should be stoped.
I tried to implement it in v3 patch.

> Wrt memory leaks, try compiling with EXTRA_CFLAGS="-fsanitize=address"
> which also incorporates leak sanitizer.

Got it,  thanks.


Best wishes
Chunxin

> 
> Thanks,
> Ian
> 
>> +                       continue;
>> +               }
>> +
>> +               if (!perf_cpu_map__is_subset(user_requested_cpus, intersect)) {
>> +                       char buf_test[128];
>> +                       char buf_intersect[128];
>> 
>> -                       cpu_map__snprint(to_test, buf, sizeof(buf));
>> -                       pr_warning("WARNING: A requested CPU in '%s' is not supported by PMU '%s' (CPUs %s) for event '%s'\n",
>> -                               cpu_list, pmu ? pmu->name : "cpu", buf, evsel__name(pos));
>> +                       cpu_map__snprint(to_test, buf_test, sizeof(buf_test));
>> +                       cpu_map__snprint(intersect, buf_intersect, sizeof(buf_intersect));
>> +                       pr_warning("WARNING: A requested CPU '%s' in '%s' is not supported by "
>> +                                  "PMU '%s' (CPUs %s) for event '%s'\n", buf_intersect, cpu_list,
>> +                                  pmu ? pmu->name : "cpu", buf_test, evsel__name(pos));
>>                }
>>                perf_cpu_map__put(intersect);
>>        }
>> --
>> 2.34.1
>>