[RFC PATCH v2 07/10] perf workqueue: implement worker thread and management

[Riccardo Mancini <rickyman7@gmail.com>]

This patch adds the implementation of the worker thread that is executed
in the threadpool, and all management-related functions.

At startup, a worker registers itself with the workqueue by adding itself
to the idle_list, then it sends an ack back to the main thread. When
creating wotkers, the main thread will wait for the related acks.
Once there is work to do, threads are woken up to perform the work.
Threads will try to dequeue a new pending work before going to sleep.

This registering mechanism has been implemented to enable for dynamic
growth of the workqueue in the future.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
---
 tools/perf/util/workqueue/workqueue.c | 243 +++++++++++++++++++++++++-
 1 file changed, 242 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/workqueue/workqueue.c b/tools/perf/util/workqueue/workqueue.c
index d3c6d4c4e75944a5..16a55de25cf247d8 100644
--- a/tools/perf/util/workqueue/workqueue.c
+++ b/tools/perf/util/workqueue/workqueue.c
@@ -12,6 +12,15 @@
 #include <internal/lib.h>
 #include "workqueue.h"
 
+enum worker_msg {
+	WORKER_MSG__UNDEFINED,
+	WORKER_MSG__READY,                          /* from worker: ack */
+	WORKER_MSG__WAKE,                           /* to worker: wake up */
+	WORKER_MSG__STOP,                           /* to worker: exit */
+	WORKER_MSG__ERROR,
+	WORKER_MSG__MAX
+};
+
 enum workqueue_status {
 	WORKQUEUE_STATUS__READY,	/* wq is ready to receive work */
 	WORKQUEUE_STATUS__ERROR,
@@ -46,13 +55,216 @@ static const char * const workqueue_errno_str[] = {
 	"Received unexpected message from worker",
 };
 
+struct worker {
+	int				tidx;		/* idx of thread in pool */
+	struct list_head		entry;		/* in idle or busy list */
+	struct work_struct		*current_work;	/* work being processed */
+	int				msg_pipe[2];	/* main thread comm pipes*/
+};
+
+#define for_each_busy_worker(wq, m_worker) \
+	list_for_each_entry(m_worker, &wq->busy_list, entry)
+
+#define for_each_idle_worker(wq, m_worker) \
+	list_for_each_entry(m_worker, &wq->idle_list, entry)
+
+static inline int lock_workqueue(struct workqueue_struct *wq)
+__acquires(&wq->lock)
+{
+	__acquire(&wq->lock);
+	return pthread_mutex_lock(&wq->lock);
+}
+
+static inline int unlock_workqueue(struct workqueue_struct *wq)
+__releases(&wq->lock)
+{
+	__release(&wq->lock);
+	return pthread_mutex_unlock(&wq->lock);
+}
+
+/**
+ * available_work - check if @wq has work to do
+ */
+static int available_work(struct workqueue_struct *wq)
+__must_hold(&wq->lock)
+{
+	return !list_empty(&wq->pending);
+}
+
+/**
+ * dequeue_work - retrieve the next work in @wq to be executed by the worker
+ *
+ * Called inside worker.
+ */
+static struct work_struct *dequeue_work(struct workqueue_struct *wq)
+__must_hold(&wq->lock)
+{
+	struct work_struct *work = list_first_entry(&wq->pending, struct work_struct, entry);
+
+	list_del_init(&work->entry);
+	return work;
+}
+
+/**
+ * sleep_worker - worker @w of workqueue @wq goes to sleep
+ *
+ * Called inside worker.
+ * If this was the last idle thread, signal it to the main thread, in case it
+ * was flushing the workqueue.
+ */
+static void sleep_worker(struct workqueue_struct *wq, struct worker *w)
+__must_hold(&wq->lock)
+{
+	list_move(&w->entry, &wq->idle_list);
+	if (list_empty(&wq->busy_list))
+		pthread_cond_signal(&wq->idle_cond);
+}
+
+/**
+ * stop_worker - stop worker @w
+ *
+ * Called from main thread.
+ * Send stop message to worker @w.
+ */
+static int stop_worker(struct worker *w)
+{
+	int ret;
+	enum worker_msg msg;
+
+	msg = WORKER_MSG__STOP;
+	ret = writen(w->msg_pipe[1], &msg, sizeof(msg));
+	if (ret < 0) {
+		pr_debug2("workqueue: error sending stop msg: %s\n",
+			strerror(errno));
+		return -WORKQUEUE_ERROR__WRITEPIPE;
+	}
+
+	return 0;
+}
+
+/**
+ * init_worker - init @w struct
+ * @w: the struct to init
+ * @tidx: index of the executing thread inside the threadpool
+ */
+static int init_worker(struct worker *w, int tidx)
+{
+	if (pipe(w->msg_pipe)) {
+		pr_debug2("worker[%d]: error opening pipe: %s\n", tidx, strerror(errno));
+		return -ENOMEM;
+	}
+
+	w->tidx = tidx;
+	w->current_work = NULL;
+	INIT_LIST_HEAD(&w->entry);
+
+	return 0;
+}
+
+/**
+ * fini_worker - deallocate resources used by @w struct
+ */
+static void fini_worker(struct worker *w)
+{
+	close(w->msg_pipe[0]);
+	w->msg_pipe[0] = -1;
+	close(w->msg_pipe[1]);
+	w->msg_pipe[1] = -1;
+}
+
+/**
+ * register_worker - add worker to @wq->idle_list
+ */
+static void register_worker(struct workqueue_struct *wq, struct worker *w)
+__must_hold(&wq->lock)
+{
+	list_move(&w->entry, &wq->idle_list);
+}
+
+/**
+ * unregister_worker - remove worker from @wq->idle_list
+ */
+static void unregister_worker(struct workqueue_struct *wq __maybe_unused,
+			struct worker *w)
+__must_hold(&wq->lock)
+{
+	list_del_init(&w->entry);
+}
+
 /**
  * worker_thread - worker function executed on threadpool
  */
 static void worker_thread(int tidx, struct task_struct *task)
 {
+	struct workqueue_struct *wq = container_of(task, struct workqueue_struct, task);
+	struct worker this_worker;
+	enum worker_msg msg;
+	int ret, init_err = init_worker(&this_worker, tidx);
+
+	if (init_err) {
+		// send error message to main thread
+		msg = WORKER_MSG__ERROR;
+	} else {
+		lock_workqueue(wq);
+		register_worker(wq, &this_worker);
+		unlock_workqueue(wq);
+
+		// ack worker creation
+		msg = WORKER_MSG__READY;
+	}
+
+	ret = writen(wq->msg_pipe[1], &msg, sizeof(msg));
+	if (ret < 0) {
+		pr_debug("worker[%d]: error sending msg: %s\n",
+			tidx, strerror(errno));
+
+		if (init_err)
+			return;
+		goto out;
+	}
 
-	pr_info("Hi from worker %d, executing task %p\n", tidx, task);
+	// stop if there have been errors in init
+	if (init_err)
+		return;
+
+	for (;;) {
+		msg = WORKER_MSG__UNDEFINED;
+		ret = readn(this_worker.msg_pipe[0], &msg, sizeof(msg));
+		if (ret < 0 || (msg != WORKER_MSG__WAKE && msg != WORKER_MSG__STOP)) {
+			pr_debug("worker[%d]: error receiving msg: %s\n",
+				tidx, strerror(errno));
+			break;
+		}
+
+		if (msg == WORKER_MSG__STOP)
+			break;
+
+		// main thread takes care of moving to busy list and assigning current_work
+
+		while (this_worker.current_work) {
+			this_worker.current_work->func(this_worker.current_work);
+
+			lock_workqueue(wq);
+			if (available_work(wq)) {
+				this_worker.current_work = dequeue_work(wq);
+				pr_debug2("worker[%d]: dequeued work\n",
+					tidx);
+			} else {
+				this_worker.current_work = NULL;
+				sleep_worker(wq, &this_worker);
+				pr_debug2("worker[%d]: going to sleep\n",
+					tidx);
+			}
+			unlock_workqueue(wq);
+		}
+	}
+
+out:
+	lock_workqueue(wq);
+	unregister_worker(wq, &this_worker);
+	unlock_workqueue(wq);
+
+	fini_worker(&this_worker);
 }
 
 /**
@@ -61,6 +273,9 @@ static void worker_thread(int tidx, struct task_struct *task)
 static int attach_threadpool_to_workqueue(struct workqueue_struct *wq,
 					struct threadpool *pool)
 {
+	int ret, t;
+	enum worker_msg msg;
+
 	if (!threadpool__is_ready(pool)) {
 		pr_debug2("workqueue: cannot attach to pool: pool is not ready\n");
 		return -WORKQUEUE_ERROR__NOTALLOWED;
@@ -72,6 +287,22 @@ static int attach_threadpool_to_workqueue(struct workqueue_struct *wq,
 	if (wq->pool_errno)
 		return -WORKQUEUE_ERROR__POOLEXE;
 
+
+	// wait ack from all threads
+	for (t = 0; t < threadpool__size(pool); t++) {
+		msg = WORKER_MSG__UNDEFINED;
+		ret = readn(wq->msg_pipe[0], &msg, sizeof(msg));
+		if (ret < 0) {
+			pr_debug("workqueue: error receiving ack: %s\n",
+				strerror(errno));
+			return -WORKQUEUE_ERROR__READPIPE;
+		}
+		if (msg != WORKER_MSG__READY) {
+			pr_debug2("workqueue: received error\n");
+			return -WORKQUEUE_ERROR__INVALIDMSG;
+		}
+	}
+
 	return 0;
 }
 
@@ -81,12 +312,22 @@ static int attach_threadpool_to_workqueue(struct workqueue_struct *wq,
 static int detach_threadpool_from_workqueue(struct workqueue_struct *wq)
 {
 	int ret, err = 0;
+	struct worker *w;
 
 	if (wq->status != WORKQUEUE_STATUS__READY) {
 		pr_debug2("workqueue: cannot attach to pool: wq is not ready\n");
 		return -WORKQUEUE_ERROR__NOTALLOWED;
 	}
 
+	lock_workqueue(wq);
+	for_each_idle_worker(wq, w) {
+		ret = stop_worker(w);
+		if (ret)
+			err = ret;
+	}
+	unlock_workqueue(wq);
+
+
 	ret = threadpool__wait(wq->pool);
 	if (ret) {
 		pr_debug2("workqueue: error waiting threadpool\n");
-- 
2.31.1