Commit 01fcb1cb authored by Jason Wang's avatar Jason Wang Committed by Michael S. Tsirkin
Browse files

vhost: allow device that does not depend on vhost worker 



vDPA device currently relays the eventfd via vhost worker. This is
inefficient due the latency of wakeup and scheduling, so this patch
tries to introduce a use_worker attribute for the vhost device. When
use_worker is not set with vhost_dev_init(), vhost won't try to
allocate a worker thread and the vhost_poll will be processed directly
in the wakeup function.

This help for vDPA since it reduces the latency caused by vhost worker.

In my testing, it saves 0.2 ms in pings between VMs on a mutual host.

Signed-off-by: default avatarZhu Lingshan <lingshan.zhu@intel.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200529080303.15449-2-jasowang@redhat.com


Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 5c1bd89b

drivers/vhost/net.c

+1 −1
Original line number Diff line number Diff line
@@ -1326,7 +1326,7 @@ static int vhost_net_open(struct inode *inode, struct file *f) 
	}

	vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX,

		       UIO_MAXIOV + VHOST_NET_BATCH,

		       VHOST_NET_PKT_WEIGHT, VHOST_NET_WEIGHT,

		       VHOST_NET_PKT_WEIGHT, VHOST_NET_WEIGHT, true,

		       NULL);



	vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, EPOLLOUT, dev);

drivers/vhost/scsi.c

+1 −1
Original line number Diff line number Diff line
@@ -1628,7 +1628,7 @@ static int vhost_scsi_open(struct inode *inode, struct file *f) 
		vs->vqs[i].vq.handle_kick = vhost_scsi_handle_kick;

	}

	vhost_dev_init(&vs->dev, vqs, VHOST_SCSI_MAX_VQ, UIO_MAXIOV,

		       VHOST_SCSI_WEIGHT, 0, NULL);

		       VHOST_SCSI_WEIGHT, 0, true, NULL);



	vhost_scsi_init_inflight(vs, NULL);

drivers/vhost/vdpa.c

+1 −1
Original line number Diff line number Diff line
@@ -694,7 +694,7 @@ static int vhost_vdpa_open(struct inode *inode, struct file *filep) 
		vqs[i] = &v->vqs[i];

		vqs[i]->handle_kick = handle_vq_kick;

	}

	vhost_dev_init(dev, vqs, nvqs, 0, 0, 0,

	vhost_dev_init(dev, vqs, nvqs, 0, 0, 0, false,

		       vhost_vdpa_process_iotlb_msg);



	dev->iotlb = vhost_iotlb_alloc(0, 0);

drivers/vhost/vhost.c

+25 −13
Original line number Diff line number Diff line
@@ -166,11 +166,16 @@ static int vhost_poll_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, 
			     void *key)

{

	struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);

	struct vhost_work *work = &poll->work;



	if (!(key_to_poll(key) & poll->mask))

		return 0;



	if (!poll->dev->use_worker)

		work->fn(work);

	else

		vhost_poll_queue(poll);



	return 0;

}
@@ -454,6 +459,7 @@ static size_t vhost_get_desc_size(struct vhost_virtqueue *vq, 
void vhost_dev_init(struct vhost_dev *dev,

		    struct vhost_virtqueue **vqs, int nvqs,

		    int iov_limit, int weight, int byte_weight,

		    bool use_worker,

		    int (*msg_handler)(struct vhost_dev *dev,

				       struct vhost_iotlb_msg *msg))

{
@@ -471,6 +477,7 @@ void vhost_dev_init(struct vhost_dev *dev, 
	dev->iov_limit = iov_limit;

	dev->weight = weight;

	dev->byte_weight = byte_weight;

	dev->use_worker = use_worker;

	dev->msg_handler = msg_handler;

	init_llist_head(&dev->work_list);

	init_waitqueue_head(&dev->wait);
@@ -549,7 +556,9 @@ long vhost_dev_set_owner(struct vhost_dev *dev) 
	/* No owner, become one */

	dev->mm = get_task_mm(current);

	dev->kcov_handle = kcov_common_handle();

	worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);

	if (dev->use_worker) {

		worker = kthread_create(vhost_worker, dev,

					"vhost-%d", current->pid);

		if (IS_ERR(worker)) {

			err = PTR_ERR(worker);

			goto err_worker;
@@ -561,6 +570,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev) 
		err = vhost_attach_cgroups(dev);

		if (err)

			goto err_cgroup;

	}



	err = vhost_dev_alloc_iovecs(dev);

	if (err)
@@ -568,8 +578,10 @@ long vhost_dev_set_owner(struct vhost_dev *dev) 


	return 0;

err_cgroup:

	kthread_stop(worker);

	if (dev->worker) {

		kthread_stop(dev->worker);

		dev->worker = NULL;

	}

err_worker:

	if (dev->mm)

		mmput(dev->mm);

drivers/vhost/vhost.h

+2 −0
Original line number Diff line number Diff line
@@ -154,6 +154,7 @@ struct vhost_dev { 
	int weight;

	int byte_weight;

	u64 kcov_handle;

	bool use_worker;

	int (*msg_handler)(struct vhost_dev *dev,

			   struct vhost_iotlb_msg *msg);

};
@@ -161,6 +162,7 @@ struct vhost_dev { 
bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);

void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs,

		    int nvqs, int iov_limit, int weight, int byte_weight,

		    bool use_worker,

		    int (*msg_handler)(struct vhost_dev *dev,

				       struct vhost_iotlb_msg *msg));

long vhost_dev_set_owner(struct vhost_dev *dev);

CRA Git | Maintained and supported by SUSTech CRA and CCSE