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Subject[tip:perf/core] perf tools: Fix comm for processes with named threads
Commit-ID:  defd8d38773cf9e01c69a903d04d5895b78ee74f
Gitweb: http://git.kernel.org/tip/defd8d38773cf9e01c69a903d04d5895b78ee74f
Author: David Ahern <dsahern@gmail.com>
AuthorDate: Thu, 22 Dec 2011 11:30:01 -0700
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Fri, 23 Dec 2011 16:10:40 -0200

perf tools: Fix comm for processes with named threads

perf does not properly handle monitoring of processes with named threads.
For example:

$ ps -C myapp -L
PID LWP TTY TIME CMD
25118 25118 ? 00:00:00 myapp
25118 25119 ? 00:00:00 myapp:worker

perf record -e cs -c 1 -fo /tmp/perf.data -p 25118 -- sleep 10
perf report --stdio -i /tmp/perf.data
100.00% myapp:worker [kernel.kallsyms] [k] perf_event_task_sched_out

The process name is set to the name of the last thread it finds for the
process.

The Problem:
perf-top and perf-record both create a thread_map of threads to be
monitored. That map is used in perf_event__synthesize_thread_map which
loops over the entries in thread_map and calls __event__synthesize_thread
to generate COMM and MMAP events.

__event__synthesize_thread calls perf_event__synthesize_comm which opens
/proc/pid/status, reads the name of the task and its thread group id.
That's all fine. The problem is that it then reads /proc/pid/task and
generates COMM events for each task it finds - but using the name found
in /proc/pid/status where pid is the thread of interest.

The end result (looping over thread_map + synthesizing comm events for
each thread each time) means the name of the last thread processed sets
the name for all threads in the process - which is not good for
multithreaded processes with named threads.

The Fix:
perf_event__synthesize_comm has an input argument (full) that decides
whether to process task entries for each pid it is passed. It currently
never set to 0 (perf_event__synthesize_comm has a single caller and it
always passes the value 1). Let's fix that.

Add the full input argument to __event__synthesize_thread which passes
it to perf_event__synthesize_comm. For thread/process monitoring set full
to 0 which means COMM and MMAP events are only generated for the pid
passed to it. For system wide monitoring set full to 1 so that COMM events
are generated for all threads in a process.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1324578603-12762-2-git-send-email-dsahern@gmail.com
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/event.c | 37 ++++++++++++++++++++++++++++++++-----
1 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index b7c7f39..a578726 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -261,11 +261,12 @@ int perf_event__synthesize_modules(struct perf_tool *tool,

static int __event__synthesize_thread(union perf_event *comm_event,
union perf_event *mmap_event,
- pid_t pid, perf_event__handler_t process,
+ pid_t pid, int full,
+ perf_event__handler_t process,
struct perf_tool *tool,
struct machine *machine)
{
- pid_t tgid = perf_event__synthesize_comm(tool, comm_event, pid, 1,
+ pid_t tgid = perf_event__synthesize_comm(tool, comm_event, pid, full,
process, machine);
if (tgid == -1)
return -1;
@@ -279,7 +280,7 @@ int perf_event__synthesize_thread_map(struct perf_tool *tool,
struct machine *machine)
{
union perf_event *comm_event, *mmap_event;
- int err = -1, thread;
+ int err = -1, thread, j;

comm_event = malloc(sizeof(comm_event->comm) + machine->id_hdr_size);
if (comm_event == NULL)
@@ -292,11 +293,37 @@ int perf_event__synthesize_thread_map(struct perf_tool *tool,
err = 0;
for (thread = 0; thread < threads->nr; ++thread) {
if (__event__synthesize_thread(comm_event, mmap_event,
- threads->map[thread],
+ threads->map[thread], 0,
process, tool, machine)) {
err = -1;
break;
}
+
+ /*
+ * comm.pid is set to thread group id by
+ * perf_event__synthesize_comm
+ */
+ if ((int) comm_event->comm.pid != threads->map[thread]) {
+ bool need_leader = true;
+
+ /* is thread group leader in thread_map? */
+ for (j = 0; j < threads->nr; ++j) {
+ if ((int) comm_event->comm.pid == threads->map[j]) {
+ need_leader = false;
+ break;
+ }
+ }
+
+ /* if not, generate events for it */
+ if (need_leader &&
+ __event__synthesize_thread(comm_event,
+ mmap_event,
+ comm_event->comm.pid, 0,
+ process, tool, machine)) {
+ err = -1;
+ break;
+ }
+ }
}
free(mmap_event);
out_free_comm:
@@ -333,7 +360,7 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
if (*end) /* only interested in proper numerical dirents */
continue;

- __event__synthesize_thread(comm_event, mmap_event, pid,
+ __event__synthesize_thread(comm_event, mmap_event, pid, 1,
process, tool, machine);
}


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