Subject: [RFC PATCH 4/4] vhost: Add cgroup-aware creation of worker threads

From: Bandan Das <[email-masked]>
Date: Mon, 13 Jul 2015 00:07:35 -0400

With the help of the cgroup function to compare groups introduced
in the previous patch, this changes worker creation policy.
If the new device belongs to different cgroups than any of the
devices we are currently serving, we end up creating a new worker
thread even if we haven't reached the devs_per_worker threshold

Signed-off-by: Bandan Das <[email-masked]>
---
 drivers/vhost/vhost.c | 47 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 39 insertions(+), 8 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 6a5d4c0..dc0fa37 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -261,12 +261,6 @@ static int vhost_worker(void *data)
 				use_mm(dev->mm);
 			}
 
-			/* TODO: Consider a more elegant solution */
-			if (worker->owner != dev->owner) {
-				/* Should check for return value */
-				cgroup_attach_task_all(dev->owner, current);
-				worker->owner = dev->owner;
-			}
 			work->fn(work);
 			if (need_resched())
 				schedule();
@@ -278,6 +272,36 @@ static int vhost_worker(void *data)
 	return 0;
 }
 
+struct vhost_attach_cgroups_struct {
+	struct vhost_work work;
+	struct task_struct *owner;
+	int ret;
+};
+
+static void vhost_attach_cgroups_work(struct vhost_work *work)
+{
+	struct vhost_attach_cgroups_struct *s;
+
+	s = container_of(work, struct vhost_attach_cgroups_struct, work);
+	s->ret = cgroup_attach_task_all(s->owner, current);
+}
+
+static void vhost_attach_cgroups(struct vhost_dev *dev,
+				struct vhost_worker *worker)
+{
+	struct vhost_attach_cgroups_struct attach;
+
+	attach.owner = dev->owner;
+	vhost_work_init(dev, &attach.work, vhost_attach_cgroups_work);
+	vhost_work_queue(worker, &attach.work);
+	vhost_work_flush(worker, &attach.work);
+
+	if (!attach.ret)
+		worker->owner = dev->owner;
+
+	dev->err = attach.ret;
+}
+
 static void vhost_create_worker(struct vhost_dev *dev)
 {
 	struct vhost_worker *worker;
@@ -300,8 +324,14 @@ static void vhost_create_worker(struct vhost_dev *dev)
 
 	spin_lock_init(&worker->work_lock);
 	INIT_LIST_HEAD(&worker->work_list);
+
+	/* attach to the cgroups of the process that created us */
+	vhost_attach_cgroups(dev, worker);
+	if (dev->err)
+		goto therror;
+	worker->owner = dev->owner;
+
 	list_add(&worker->node, &pool->workers);
-	worker->owner = NULL;
 	worker->num_devices++;
 	total_vhost_workers++;
 	dev->worker = worker;
@@ -320,7 +350,8 @@ static int vhost_dev_assign_worker(struct vhost_dev *dev)
 
 	mutex_lock(&vhost_pool->pool_lock);
 	list_for_each_entry(worker, &vhost_pool->workers, node) {
-		if (worker->num_devices < devs_per_worker) {
+		if (worker->num_devices < devs_per_worker &&
+		    (!cgroup_match_groups(dev->owner, worker->owner))) {
 			dev->worker = worker;
 			dev->worker_assigned = true;
 			worker->num_devices++;
-- 
2.4.3