Commit 30626e08 authored by Namhyung Kim's avatar Namhyung Kim Committed by Arnaldo Carvalho de Melo
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perf tools: Use /proc/<PID>/task/<TID>/status for PERF_RECORD_ event synthesis 



To save memory usage, it needs to reduce the number of entries in the
proc filesystem.  It's using /proc/<PID>/task directory to traverse
threads in the process and then kernel creates /proc/<PID>/task/<TID>
entries.

After that it checks the thread info using the /proc/<TID>/status file
rather than /proc/<PID>/task/<TID>/status.  As far as I can see, they
are the same and contain all the info we need.

Using the latter eliminates the unnecessary /proc/<TID> entry.  This can
be useful especially a large number of threads are used in the system.
In my experiment around 1KB of memory on average was saved for each
thread (which is not a thread group leader).

To do this, pass both pid and tid to perf_event_prepare_comm() if it
knows them.  In case it doesn't know, passing 0 as pid will do the old
way.

Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
Acked-by: default avatarJiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20210202090118.2008551-2-namhyung@kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent c3a9cdef

tools/perf/util/synthetic-events.c

+14 −11
Original line number Diff line number Diff line
@@ -69,7 +69,7 @@ int perf_tool__process_synth_event(struct perf_tool *tool, 
 * Assumes that the first 4095 bytes of /proc/pid/stat contains

 * the comm, tgid and ppid.

 */

static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len,

static int perf_event__get_comm_ids(pid_t pid, pid_t tid, char *comm, size_t len,

				    pid_t *tgid, pid_t *ppid)

{

	char bf[4096];
@@ -81,7 +81,10 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len, 
	*tgid = -1;

	*ppid = -1;



	snprintf(bf, sizeof(bf), "/proc/%d/status", pid);

	if (pid)

		snprintf(bf, sizeof(bf), "/proc/%d/task/%d/status", pid, tid);

	else

		snprintf(bf, sizeof(bf), "/proc/%d/status", tid);



	fd = open(bf, O_RDONLY);

	if (fd < 0) {
@@ -93,7 +96,7 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len, 
	close(fd);

	if (n <= 0) {

		pr_warning("Couldn't get COMM, tigd and ppid for pid %d\n",

			   pid);

			   tid);

		return -1;

	}

	bf[n] = '\0';
@@ -116,27 +119,27 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len, 
		memcpy(comm, name, size);

		comm[size] = '\0';

	} else {

		pr_debug("Name: string not found for pid %d\n", pid);

		pr_debug("Name: string not found for pid %d\n", tid);

	}



	if (tgids) {

		tgids += 5;  /* strlen("Tgid:") */

		*tgid = atoi(tgids);

	} else {

		pr_debug("Tgid: string not found for pid %d\n", pid);

		pr_debug("Tgid: string not found for pid %d\n", tid);

	}



	if (ppids) {

		ppids += 5;  /* strlen("PPid:") */

		*ppid = atoi(ppids);

	} else {

		pr_debug("PPid: string not found for pid %d\n", pid);

		pr_debug("PPid: string not found for pid %d\n", tid);

	}



	return 0;

}



static int perf_event__prepare_comm(union perf_event *event, pid_t pid,

static int perf_event__prepare_comm(union perf_event *event, pid_t pid, pid_t tid,

				    struct machine *machine,

				    pid_t *tgid, pid_t *ppid)

{
@@ -147,7 +150,7 @@ static int perf_event__prepare_comm(union perf_event *event, pid_t pid, 
	memset(&event->comm, 0, sizeof(event->comm));



	if (machine__is_host(machine)) {

		if (perf_event__get_comm_ids(pid, event->comm.comm,

		if (perf_event__get_comm_ids(pid, tid, event->comm.comm,

					     sizeof(event->comm.comm),

					     tgid, ppid) != 0) {

			return -1;
@@ -168,7 +171,7 @@ static int perf_event__prepare_comm(union perf_event *event, pid_t pid, 
	event->comm.header.size = (sizeof(event->comm) -

				(sizeof(event->comm.comm) - size) +

				machine->id_hdr_size);

	event->comm.tid = pid;

	event->comm.tid = tid;



	return 0;

}
@@ -180,7 +183,7 @@ pid_t perf_event__synthesize_comm(struct perf_tool *tool, 
{

	pid_t tgid, ppid;



	if (perf_event__prepare_comm(event, pid, machine, &tgid, &ppid) != 0)

	if (perf_event__prepare_comm(event, 0, pid, machine, &tgid, &ppid) != 0)

		return -1;



	if (perf_tool__process_synth_event(tool, event, machine, process) != 0)
@@ -746,7 +749,7 @@ static int __event__synthesize_thread(union perf_event *comm_event, 
			continue;



		rc = -1;

		if (perf_event__prepare_comm(comm_event, _pid, machine,

		if (perf_event__prepare_comm(comm_event, pid, _pid, machine,

					     &tgid, &ppid) != 0)

			break;