perf report: Don't bother locking when adding hist entries

The 'perf report'command is single-threaded, so no need to grab a lock.

Although the fast path of pthread_mutex_[un]lock() is very fast, there's
a ~3% gain by eliminating it when we have huge sample data.

  $ perf record -a -F 100000 -o perf.data.bench -- perf bench sched all
  $ perf record -e cycles:upp -o perf.data.before -- \
  > perf report -i perf.data.bench --stdio > /dev/null
  ... apply this patch ...
  $ perf record -e cycles:upp -o perf.data.after -- \
  > perf report -i perf.data.bench --stdio > /dev/null
  $ perf diff perf.data.{before,after} | grep pthread
             +0.02%  libpthread-2.15.so  [.] _pthread_cleanup_push_defer
             +0.02%  libpthread-2.15.so  [.] _pthread_cleanup_pop_restore
     0.05%   -0.05%  perf                [.] pthread_mutex_unlock@plt
     0.05%   -0.05%  perf                [.] pthread_mutex_lock@plt
     1.01%   -1.01%  libpthread-2.15.so  [.] pthread_mutex_lock
     1.68%   -1.68%  libpthread-2.15.so  [.] __pthread_mutex_unlock_usercnt
     0.05%   -0.05%  libpthread-2.15.so  [.] pthread_mutex_unlock

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1368497347-9628-6-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -312,8 +312,6 @@ static int process_sample_event(struct perf_tool *tool,
 	if (rep->cpu_list && !test_bit(sample->cpu, rep->cpu_bitmap))
 		return 0;
 
-	pthread_mutex_lock(&evsel->hists.lock);
-
 	if (sort__mode == SORT_MODE__BRANCH) {
 		ret = perf_report__add_branch_hist_entry(tool, &al, sample,
 							 evsel, machine);
@@ -332,8 +330,6 @@ static int process_sample_event(struct perf_tool *tool,
 		if (ret < 0)
 			pr_debug("problem incrementing symbol period, skipping event\n");
 	}
-	pthread_mutex_unlock(&evsel->hists.lock);
-
 	return ret;
 }