We use spinlock to synchronize the work list now which may cause
unnecessary contentions. So this patch switch to use llist to remove
this contention. Pktgen tests shows about 5% improvement:
Before:
~1300000 pps
After:
~1370000 pps
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
drivers/vhost/vhost.c | 52 +++++++++++++++++++++++++--------------------------
drivers/vhost/vhost.h | 7 ++++---
2 files changed, 29 insertions(+), 30 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 73dd16d..0061a7b 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -168,7 +168,7 @@ static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
{
- INIT_LIST_HEAD(&work->node);
+ clear_bit(VHOST_WORK_QUEUED, &work->flags);
work->fn = fn;
init_waitqueue_head(&work->done);
}
@@ -246,15 +246,16 @@ EXPORT_SYMBOL_GPL(vhost_poll_flush);
void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
{
- unsigned long flags;
+ if (!dev->worker)
+ return;
- spin_lock_irqsave(&dev->work_lock, flags);
- if (list_empty(&work->node)) {
- list_add_tail(&work->node, &dev->work_list);
- spin_unlock_irqrestore(&dev->work_lock, flags);
+ if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
+ /* We can only add the work to the list after we're
+ * sure it was not in the list.
+ */
+ smp_mb();
+ llist_add(&work->node, &dev->work_list);
wake_up_process(dev->worker);
- } else {
- spin_unlock_irqrestore(&dev->work_lock, flags);
}
}
EXPORT_SYMBOL_GPL(vhost_work_queue);
@@ -262,7 +263,7 @@ EXPORT_SYMBOL_GPL(vhost_work_queue);
/* A lockless hint for busy polling code to exit the loop */
bool vhost_has_work(struct vhost_dev *dev)
{
- return !list_empty(&dev->work_list);
+ return !llist_empty(&dev->work_list);
}
EXPORT_SYMBOL_GPL(vhost_has_work);
@@ -305,7 +306,8 @@ static void vhost_vq_reset(struct vhost_dev *dev,
static int vhost_worker(void *data)
{
struct vhost_dev *dev = data;
- struct vhost_work *work = NULL;
+ struct vhost_work *work, *work_next;
+ struct llist_node *node;
mm_segment_t oldfs = get_fs();
set_fs(USER_DS);
@@ -315,29 +317,25 @@ static int vhost_worker(void *data)
/* mb paired w/ kthread_stop */
set_current_state(TASK_INTERRUPTIBLE);
- spin_lock_irq(&dev->work_lock);
-
if (kthread_should_stop()) {
- spin_unlock_irq(&dev->work_lock);
__set_current_state(TASK_RUNNING);
break;
}
- if (!list_empty(&dev->work_list)) {
- work = list_first_entry(&dev->work_list,
- struct vhost_work, node);
- list_del_init(&work->node);
- } else
- work = NULL;
- spin_unlock_irq(&dev->work_lock);
- if (work) {
+ node = llist_del_all(&dev->work_list);
+ if (!node)
+ schedule();
+
+ node = llist_reverse_order(node);
+ /* make sure flag is seen after deletion */
+ smp_wmb();
+ llist_for_each_entry_safe(work, work_next, node, node) {
+ clear_bit(VHOST_WORK_QUEUED, &work->flags);
__set_current_state(TASK_RUNNING);
work->fn(work);
if (need_resched())
schedule();
- } else
- schedule();
-
+ }
}
unuse_mm(dev->mm);
set_fs(oldfs);
@@ -398,9 +396,9 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->log_file = NULL;
dev->memory = NULL;
dev->mm = NULL;
- spin_lock_init(&dev->work_lock);
- INIT_LIST_HEAD(&dev->work_list);
dev->worker = NULL;
+ init_llist_head(&dev->work_list);
+
for (i = 0; i < dev->nvqs; ++i) {
vq = dev->vqs[i];
@@ -566,7 +564,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
/* No one will access memory at this point */
kvfree(dev->memory);
dev->memory = NULL;
- WARN_ON(!list_empty(&dev->work_list));
+ WARN_ON(!llist_empty(&dev->work_list));
if (dev->worker) {
kthread_stop(dev->worker);
dev->worker = NULL;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index d36d8be..6690e64 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -15,13 +15,15 @@
struct vhost_work;
typedef void (*vhost_work_fn_t)(struct vhost_work *work);
+#define VHOST_WORK_QUEUED 1
struct vhost_work {
- struct list_head node;
+ struct llist_node node;
vhost_work_fn_t fn;
wait_queue_head_t done;
int flushing;
unsigned queue_seq;
unsigned done_seq;
+ unsigned long flags;
};
/* Poll a file (eventfd or socket) */
@@ -126,8 +128,7 @@ struct vhost_dev {
int nvqs;
struct file *log_file;
struct eventfd_ctx *log_ctx;
- spinlock_t work_lock;
- struct list_head work_list;
+ struct llist_head work_list;
struct task_struct *worker;
};
--
1.8.3.1
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