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vhost: allow device that does not depend on vhost worker

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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: Zhu Lingshan <lingshan.zhu@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200529080303.15449-2-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Jason Wang 2020-05-29 16:02:58 +08:00 committed by Michael S. Tsirkin
parent 5c1bd89b45
commit 01fcb1cbc8
6 changed files with 32 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/vhost/net.c
View File

@ -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);

2
drivers/vhost/scsi.c
View File

@ -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);

2
drivers/vhost/vdpa.c
View File

@ -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);

40
drivers/vhost/vhost.c
View File

@ -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;
vhost_poll_queue(poll);
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);
@ -549,27 +556,32 @@ 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 (IS_ERR(worker)) {
err = PTR_ERR(worker);
goto err_worker;
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;
}
dev->worker = worker;
wake_up_process(worker); /* avoid contributing to loadavg */
err = vhost_attach_cgroups(dev);
if (err)
goto err_cgroup;
}
dev->worker = worker;
wake_up_process(worker); /* avoid contributing to loadavg */
err = vhost_attach_cgroups(dev);
if (err)
goto err_cgroup;
err = vhost_dev_alloc_iovecs(dev);
if (err)
goto err_cgroup;
return 0;
err_cgroup:
kthread_stop(worker);
dev->worker = NULL;
if (dev->worker) {
kthread_stop(dev->worker);
dev->worker = NULL;
}
err_worker:
if (dev->mm)
mmput(dev->mm);

2
drivers/vhost/vhost.h
View File

@ -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);

2
drivers/vhost/vsock.c
View File

@ -632,7 +632,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
vhost_dev_init(&vsock->dev, vqs, ARRAY_SIZE(vsock->vqs),
UIO_MAXIOV, VHOST_VSOCK_PKT_WEIGHT,
VHOST_VSOCK_WEIGHT, NULL);
VHOST_VSOCK_WEIGHT, true, NULL);
file->private_data = vsock;
spin_lock_init(&vsock->send_pkt_list_lock);