Skip to contentSkip to conversation

perf top: Use cond variable instead of a lock

tip:perf/core tip-bot for Jiri Olsa 1 participant 1 message Dec 14, 2018 perf events

lore
Share & tools
lore

tip-bot for Jiri Olsa

author merge bot
#0 lore raw
Commit-ID:  bc67057cab13c1571de499e94d491e6115da86c9
Gitweb:     https://git.kernel.org/tip/bc67057cab13c1571de499e94d491e6115da86c9
Author:     Jiri Olsa <[email protected]>
AuthorDate: Mon, 5 Nov 2018 21:23:40 +0100
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Thu, 6 Dec 2018 14:12:33 -0300

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.

Acked-by David S. Miller <[email protected]>
Acked-by Namhyung Kim <[email protected]>
Tested-by Arnaldo Carvalho de Melo <[email protected]>
Cc Alexander Shishkin <[email protected]>
Cc Peter Zijlstra <[email protected]>
Link http://lkml.kernel.org/n/[email protected] open here
Signed-off-by Jiri Olsa <[email protected]>
---
 tools/perf/builtin-top.c | 24 +++++++++++++++++-------
 tools/perf/util/top.h    |  4 +++-
 2 files changed, 20 insertions(+), 8 deletions(-)
tools/perf/builtin-top.c +17 -7
index 75afeae7f04d..aad58643102e 100644
@@ -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);
tools/perf/util/top.h +3 -1
index 5f503293cfd8..5bce62ebcf14 100644
@@ -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;
 };