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vhost: lockless enqueuing 

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@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
hifive-unleashed-5.1
Jason Wang 2016-04-25 22:14:33 -04:00 committed by Michael S. Tsirkin
parent 7235acdb11
commit 04b96e5528
2 changed files with 29 additions and 30 deletions
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52
drivers/vhost/vhost.c
View File

@ -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;

7
drivers/vhost/vhost.h
View File

@ -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;
};