Ning Bo reported an abnormal 2-second gap when booting Kata container [1].
The unconditional timeout was caused by VSOCK_DEFAULT_CONNECT_TIMEOUT of
connecting from the client side. The vhost vsock client tries to connect
an initializing virtio vsock server.
The abnormal flow looks like:
host-userspace vhost vsock guest vsock
============== =========== ============
connect() --------> vhost_transport_send_pkt_work() initializing
| vq->private_data==NULL
| will not be queued
V
schedule_timeout(2s)
vhost_vsock_start() <--------- device ready
set vq->private_data
wait for 2s and failed
connect() again vq->private_data!=NULL recv connecting pkt
Details:
1. Host userspace sends a connect pkt, at that time, guest vsock is under
initializing, hence the vhost_vsock_start has not been called. So
vq->private_data==NULL, and the pkt is not been queued to send to guest
2. Then it sleeps for 2s
3. After guest vsock finishes initializing, vq->private_data is set
4. When host userspace wakes up after 2s, send connecting pkt again,
everything is fine.
As suggested by Stefano Garzarella, this fixes it by additional kicking the
send_pkt worker in vhost_vsock_start once the virtio device is started. This
makes the pending pkt sent again.
After this patch, kata-runtime (with vsock enabled) boot time is reduced
from 3s to 1s on a ThunderX2 arm64 server.
[1] https://github.com/kata-containers/runtime/issues/1917
Reported-by: Ning Bo <n...@live.com>
Suggested-by: Stefano Garzarella <sgarz...@redhat.com>
Signed-off-by: Jia He <justin...@arm.com>
---
v2: new solution suggested by Stefano Garzarella
drivers/vhost/vsock.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index e36aaf9ba7bd..0716a9cdffee 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -543,6 +543,11 @@ static int vhost_vsock_start(struct vhost_vsock *vsock)
mutex_unlock(&vq->mutex);
}
+ /* Some packets may have been queued before the device was started,
+ * let's kick the send worker to send them.
+ */
+ vhost_work_queue(&vsock->dev, &vsock->send_pkt_work);
+
mutex_unlock(&vsock->dev.mutex);
return 0;
--
2.17.1
