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

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Message-ID: <549D8C59.1000700@gmail.com>
Date:	Fri, 26 Dec 2014 09:27:05 -0700
From:	David Ahern <dsahern@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 02/37] perf record: Use a software dummy event to track
 task/mmap events

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?

---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()?

David

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