[PATCH v3 05/12] perf record: start threads in the beginning of trace streaming

[Alexey Budankov]

Start thread in detached state because its management is implemented
via messaging to avoid any scaling issues. Block signals prior thread
start so only main tool thread would be notified on external async
signals during data collection. Thread affinity mask is used to assign
eligible cpus for the thread to run. Wait and sync on thread start using
thread comm.ack pipe.

Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
---
 tools/perf/builtin-record.c | 103 +++++++++++++++++++++++++++++++++++-
 1 file changed, 102 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index d0b528cde68b..13773739bedc 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1407,6 +1407,64 @@ static void record__thread_munmap_filtered(struct fdarray *fda, int fd,
 		perf_mmap__put(map);
 }
 
+static void *record__thread(void *arg)
+{
+	enum thread_msg msg = THREAD_MSG__READY;
+	bool terminate = false;
+	struct fdarray *pollfd;
+	int err, ctlfd_pos;
+
+	thread = arg;
+	thread->tid = syscall(SYS_gettid);
+
+	err = write(thread->comm.ack[1], &msg, sizeof(msg));
+	if (err == -1)
+		pr_err("threads[%d]: failed to notify on start. Error %m", thread->tid);
+
+	pr_debug("threads[%d]: started on cpu=%d\n", thread->tid, sched_getcpu());
+
+	pollfd = &thread->pollfd;
+	ctlfd_pos = thread->ctlfd_pos;
+
+	for (;;) {
+		unsigned long long hits = thread->samples;
+
+		if (record__mmap_read_all(thread->rec, false) < 0 || terminate)
+			break;
+
+		if (hits == thread->samples) {
+
+			err = fdarray__poll(pollfd, -1);
+			/*
+			 * Propagate error, only if there's any. Ignore positive
+			 * number of returned events and interrupt error.
+			 */
+			if (err > 0 || (err < 0 && errno == EINTR))
+				err = 0;
+			thread->waking++;
+
+			if (fdarray__filter(pollfd, POLLERR | POLLHUP,
+					    record__thread_munmap_filtered, NULL) == 0)
+				break;
+		}
+
+		if (pollfd->entries[ctlfd_pos].revents & POLLHUP) {
+			terminate = true;
+			close(thread->comm.msg[0]);
+			pollfd->entries[ctlfd_pos].fd = -1;
+			pollfd->entries[ctlfd_pos].events = 0;
+		}
+
+		pollfd->entries[ctlfd_pos].revents = 0;
+	}
+
+	err = write(thread->comm.ack[1], &msg, sizeof(msg));
+	if (err == -1)
+		pr_err("threads[%d]: failed to notify on termination. Error %m", thread->tid);
+
+	return NULL;
+}
+
 static void record__init_features(struct record *rec)
 {
 	struct perf_session *session = rec->session;
@@ -1847,13 +1905,56 @@ static int record__terminate_thread(struct thread_data *thread_data)
 
 static int record__start_threads(struct record *rec)
 {
+	int t, tt, ret = 0, nr_threads = rec->nr_threads;
 	struct thread_data *thread_data = rec->thread_data;
+	sigset_t full, mask;
+	pthread_t handle;
+	pthread_attr_t attrs;
+
+	sigfillset(&full);
+	if (sigprocmask(SIG_SETMASK, &full, &mask)) {
+		pr_err("Failed to block signals on threads start. Error: %m\n");
+		return -1;
+	}
+
+	pthread_attr_init(&attrs);
+	pthread_attr_setdetachstate(&attrs, PTHREAD_CREATE_DETACHED);
+
+	for (t = 1; t < nr_threads; t++) {
+		enum thread_msg msg = THREAD_MSG__UNDEFINED;
+
+		pthread_attr_setaffinity_np(&attrs, MMAP_CPU_MASK_BYTES(&(thread_data[t].mask->affinity)),
+					    (cpu_set_t *)(thread_data[t].mask->affinity.bits));
+
+		if (pthread_create(&handle, &attrs, record__thread, &thread_data[t])) {
+			for (tt = 1; tt < t; tt++)
+				record__terminate_thread(&thread_data[t]);
+			pr_err("Failed to start threads. Error: %m\n");
+			ret = -1;
+			goto out_err;
+		}
+
+		if (read(thread_data[t].comm.ack[0], &msg, sizeof(msg)) > 0)
+			pr_debug("threads[%d]: sent %s\n", rec->thread_data[t].tid,
+				 thread_msg_tags[msg]);
+	}
+
+	if (nr_threads > 1) {
+		sched_setaffinity(0, MMAP_CPU_MASK_BYTES(&thread_data[0].mask->affinity),
+				  (cpu_set_t *)thread_data[0].mask->affinity.bits);
+	}
 
 	thread = &thread_data[0];
 
 	pr_debug("threads[%d]: started on cpu=%d\n", thread->tid, sched_getcpu());
 
-	return 0;
+out_err:
+	if (sigprocmask(SIG_SETMASK, &mask, NULL)) {
+		pr_err("Failed to unblock signals on threads start. Error: %m\n");
+		ret = -1;
+	}
+
+	return ret;
 }
 
 static int record__stop_threads(struct record *rec, unsigned long *waking)
-- 
2.24.1