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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 18 Jul 2019 04:13:26 -0400

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 <[email-masked]> wrote:
> >
> > On Wed, Jul 17, 2019 at 01:30:29PM +0200, Stefano Garzarella wrote:
> > > 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 <[email-masked]>
> >
> > 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