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>

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 75afeae7f04d3bc3f20b2e900d81ea408b91e6b2..aad58643102eda7cf48b6c5b28a20e9ecfd8e782 100644 (file)
--- 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 5f503293cfd8356fe1099ef6cb33df2baeb1fd02..5bce62ebcf147e518b26bc93d4677b5cb2b9b828 100644 (file)
--- 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;
 };