perf top: Use cond variable instead of a lock

Use conditional variable logic to synchronize between the reading and
processing threads. Currently it's done by having mutex around rotation
code.

Using a POSIX cond variable to sync both threads after queues rotation:

  Process thread:

    - Detects data
    - Switches queues
    - Sets rotate variable
    - Waits in pthread_cond_wait()

  Read thread:

    - Detects rotate is set
    - Kicks the process thread with a pthread_cond_signal()

After this rotation is safely completed and both threads can continue
with the new queue.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-3rdeg23rv3brvy1pwt3igvyw@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 20 insertions, 8 deletions

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 75afeae7f04d..aad58643102e 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -846,13 +846,18 @@ static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
                 if (ret && ret != -1)
                         break;
 
-                pthread_mutex_lock(&top->qe.lock);
                 ret = ordered_events__queue(top->qe.in, event, timestamp, 0);
-                pthread_mutex_unlock(&top->qe.lock);
-
-                perf_mmap__consume(md);
                 if (ret)
                         break;
+
+                perf_mmap__consume(md);
+
+                if (top->qe.rotate) {
+                        pthread_mutex_lock(&top->qe.mutex);
+                        top->qe.rotate = false;
+                        pthread_cond_signal(&top->qe.cond);
+                        pthread_mutex_unlock(&top->qe.mutex);
+                }
         }
 
         perf_mmap__read_done(md);
@@ -1059,9 +1064,12 @@ static void *process_thread(void *arg)
                         continue;
                 }
 
-                pthread_mutex_lock(&top->qe.lock);
                 out = rotate_queues(top);
-                pthread_mutex_unlock(&top->qe.lock);
+
+                pthread_mutex_lock(&top->qe.mutex);
+                top->qe.rotate = true;
+                pthread_cond_wait(&top->qe.cond, &top->qe.mutex);
+                pthread_mutex_unlock(&top->qe.mutex);
 
                 if (ordered_events__flush(out, OE_FLUSH__TOP))
                         pr_err("failed to process events\n");
@@ -1151,7 +1159,8 @@ static void init_process_thread(struct perf_top *top)
         ordered_events__set_copy_on_queue(&top->qe.data[0], true);
         ordered_events__set_copy_on_queue(&top->qe.data[1], true);
         top->qe.in = &top->qe.data[0];
-        pthread_mutex_init(&top->qe.lock, NULL);
+        pthread_mutex_init(&top->qe.mutex, NULL);
+        pthread_cond_init(&top->qe.cond, NULL);
 }
 
 static int __cmd_top(struct perf_top *top)
@@ -1271,6 +1280,7 @@ static int __cmd_top(struct perf_top *top)
 out_join:
         pthread_join(thread, NULL);
 out_join_thread:
+        pthread_cond_signal(&top->qe.cond);
         pthread_join(thread_process, NULL);
 out_delete:
         perf_session__delete(top->session);
diff --git a/tools/perf/util/top.h b/tools/perf/util/top.h
index 5f503293cfd8..5bce62ebcf14 100644
--- a/tools/perf/util/top.h
+++ b/tools/perf/util/top.h
@@ -44,7 +44,9 @@ struct perf_top {
         struct {
                 struct ordered_events   *in;
                 struct ordered_events    data[2];
-                pthread_mutex_t          lock;
+                bool                     rotate;
+                pthread_mutex_t          mutex;
+                pthread_cond_t           cond;
         } qe;
 };