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SubjectRe: [PATCH 02/37] perf record: Use a software dummy event to track task/mmap events
Hi David,

On Sat, Dec 27, 2014 at 1:27 AM, David Ahern <dsahern@gmail.com> 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,
>> + };
>> + 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.

Thanks,
Namhyung


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