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

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Date:   Thu, 18 Jul 2019 09:50:14 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org,
        Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH v4 4/5] vhost/vsock: split packets to send using multiple
 buffers

On Wed, Jul 17, 2019 at 4:55 PM Michael S. Tsirkin <mst@...hat.com> 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 <sgarzare@...hat.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)

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

Thanks,
Stefano