Re: [PATCH v4 4/5] vhost/vsock: split packets to send using multiple buffers

On Thu, Jul 18, 2019 at 09:50:14AM +0200, Stefano Garzarella wrote:

On Wed, Jul 17, 2019 at 4:55 PM Michael S. Tsirkin [off-list ref] wrote:

quoted

On Wed, Jul 17, 2019 at 01:30:29PM +0200, Stefano Garzarella wrote:

quoted

If the packets to sent to the guest are bigger than the buffer
available, we can split them, using multiple buffers and fixing
the length in the packet header.
This is safe since virtio-vsock supports only stream sockets.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

So how does it work right now? If an app
does sendmsg with a 64K buffer and the other
side publishes 4K buffers - does it just stall?

Before this series, the 64K (or bigger) user messages was split in 4K packets
(fixed in the code) and queued in an internal list for the TX worker.

After this series, we will queue up to 64K packets and then it will be split in
the TX worker, depending on the size of the buffers available in the
vring. (The idea was to allow EWMA or a configuration of the buffers size, but
for now we postponed it)

Got it. Using workers for xmit is IMHO a bad idea btw.
Why is it done like this?

Note: virtio-vsock only supports stream socket for now.

Thanks,
Stefano