Re: [PATCH v2 5/5] perf parse-events: Add debug dump of evlist if reordered

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2025-04-02 2:15 p.m., Ian Rogers wrote:
> On Wed, Apr 2, 2025 at 10:52 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
>>
>>
>>
>> On 2025-04-02 12:47 p.m., Ian Rogers wrote:
>>> Add debug verbose output to show how evsels were reordered by
>>> parse_events__sort_events_and_fix_groups. For example:
>>> ```
>>> $ perf record -v -e '{instructions,cycles}' true
>>> Using CPUID GenuineIntel-6-B7-1
>>> WARNING: events were regrouped to match PMUs
>>> evlist after sorting/fixing: '{cpu_atom/instructions/,cpu_atom/cycles/},{cpu_core/instructions/,cpu_core/cycles/}'
>>> ```
>>>
>>> Signed-off-by: Ian Rogers <irogers@google.com>
>>> ---
>>>  tools/perf/util/parse-events.c | 16 +++++++++++++---
>>>  1 file changed, 13 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
>>> index 5152fd5a6ead..0f8fd5bee3a7 100644
>>> --- a/tools/perf/util/parse-events.c
>>> +++ b/tools/perf/util/parse-events.c
>>> @@ -28,6 +28,7 @@
>>>  #include "util/evsel_config.h"
>>>  #include "util/event.h"
>>>  #include "util/bpf-filter.h"
>>> +#include "util/stat.h"
>>>  #include "util/util.h"
>>>  #include "tracepoint.h"
>>>
>>> @@ -2196,14 +2197,23 @@ int __parse_events(struct evlist *evlist, const char *str, const char *pmu_filte
>>>       if (ret2 < 0)
>>>               return ret;
>>>
>>> -     if (ret2 && warn_if_reordered && !parse_state.wild_card_pmus)
>>> -             pr_warning("WARNING: events were regrouped to match PMUs\n");
>>> -
>>>       /*
>>>        * Add list to the evlist even with errors to allow callers to clean up.
>>>        */
>>>       evlist__splice_list_tail(evlist, &parse_state.list);
>>>
>>> +     if (ret2 && warn_if_reordered && !parse_state.wild_card_pmus) {
>>> +             pr_warning("WARNING: events were regrouped to match PMUs\n");
>>> +
>>> +             if (verbose > 0) {
>>> +                     struct strbuf sb = STRBUF_INIT;
>>> +
>>> +                     evlist__uniquify_name(evlist);
>>> +                     evlist__format_evsels(evlist, &sb, 1024);
>>
>> Why is the size even less than the one in pr_err?
>>
>> The user probably prefer to get the complete list in the debug.
> 
> I thought the previous 2048 excessive but kept it for the previous
> case to not change anything. If you are happier with 2048 here I don't
> particularly mind, it is a lot to display in verbose output.

Yes, I think the verbose output wouldn't bother the normal user. We only
use it when there is a problem. So detailed information should be
preferred.

Thanks,
Kan>
> Thanks,
> Ian
> 
>> Thanks,
>> Kan> +                  pr_debug("evlist after sorting/fixing: '%s'\n", sb.buf);
>>> +                     strbuf_release(&sb);
>>> +             }
>>> +     }
>>>       if (!ret) {
>>>               struct evsel *last;
>>>
>>
>