Re: [PATCH 02/37] perf record: Use a software dummy event to track task/mmap events

[Adrian Hunter]

On 27/12/14 07:28, Namhyung Kim wrote:
> Hi David,
> 
> On Sat, Dec 27, 2014 at 1:27 AM, David Ahern <dsahern@xxxxxxxxx> wrote:
>> On 12/24/14 12:14 AM, Namhyung Kim wrote:
>>>
>>> Prepend a software dummy event into evlist to track task/comm/mmap
>>> events separately.  This is a preparation of multi-file/thread support
>>> which will come later.
>>
>>
>> Are you are making this the first event because of how perf internals are
>> coded -- that the first event tracks tasks events? With the tracking bit in
>> evsel you should not need to do that. Is there another reason?
> 
> Yeah, I know the tracking bit can be set to any evsel in the evlist.
> But I'd like to keep it at a fixed index so that it can be easily
> identified at later stages (like perf report) too.  Ideally, it'd be
> great if we have a way to distinguish this auto-added dummy tracking
> event from other (user-added) (dummy?) tracking events if any.
> 
>>
>> ---8<---
>>
>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>>> index cfbe2b99b9aa..72dff295237e 100644
>>> --- a/tools/perf/util/evlist.c
>>> +++ b/tools/perf/util/evlist.c
>>> @@ -193,6 +193,44 @@ int perf_evlist__add_default(struct perf_evlist
>>> *evlist)
>>>         return -ENOMEM;
>>>   }
>>>
>>> +int perf_evlist__prepend_dummy(struct perf_evlist *evlist)
>>> +{
>>> +       struct perf_event_attr attr = {
>>> +               .type = PERF_TYPE_SOFTWARE,
>>> +               .config = PERF_COUNT_SW_DUMMY,

Probably need .exclude_kernel = 1, here

>>> +       };
>>> +       struct perf_evsel *evsel, *pos;
>>> +
>>> +       event_attr_init(&attr);
>>> +
>>> +       evsel = perf_evsel__new(&attr);
>>> +       if (evsel == NULL)
>>> +               goto error;
>>> +
>>> +       /* use strdup() because free(evsel) assumes name is allocated */
>>> +       evsel->name = strdup("dummy");
>>> +       if (!evsel->name)
>>> +               goto error_free;
>>> +
>>> +       list_for_each_entry(pos, &evlist->entries, node) {
>>> +               pos->idx += 1;
>>> +               pos->tracking = false;
>>> +       }
>>> +
>>> +       list_add(&evsel->node, &evlist->entries);
>>> +       evsel->idx = 0;
>>> +       evsel->tracking = true;
>>
>>
>> perf_evlist__set_tracking_event()?
> 
> I found that after I wrote this, so yes, it can use the function
> instead of the oped-code.  But the loop traversal is needed anyway to
> fixup the evsel->idx.

perf_evlist__set_tracking_event() also ensures there is only one tracking
event so it is easy to identify. It is the only event with attr->mmap etc
set to 1. Then you can use perf_evlist__add().

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