Linux Virtualization - Jul 2019 - [PATCH v4 5/5] vsock/virtio: change the maximum packet size allowed

On Wed, Jul 17, 2019 at 01:30:30PM +0200, Stefano Garzarella
wrote:
> Since now we are able to split packets, we can avoid limiting
> their sizes to VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE.
> Instead, we can use VIRTIO_VSOCK_MAX_PKT_BUF_SIZE as the max
> packet size.
> 
> Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>

OK so this is kind of like GSO where we are passing
64K packets to the vsock and then split at the
low level.

> ---
>  net/vmw_vsock/virtio_transport_common.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
> index 56fab3f03d0e..94cc0fa3e848 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -181,8 +181,8 @@ static int virtio_transport_send_pkt_info(struct
vsock_sock *vsk,
>  	vvs = vsk->trans;
>  
>  	/* we can send less than pkt_len bytes */
> -	if (pkt_len > VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE)
> -		pkt_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> +	if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
> +		pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>  
>  	/* virtio_transport_get_credit might return less than pkt_len credit */
>  	pkt_len = virtio_transport_get_credit(vvs, pkt_len);
> -- 
> 2.20.1

On Wed, Jul 17, 2019 at 5:00 PM Michael S. Tsirkin <mst at redhat.com>
wrote:
>
> On Wed, Jul 17, 2019 at 01:30:30PM +0200, Stefano Garzarella wrote:
> > Since now we are able to split packets, we can avoid limiting
> > their sizes to VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE.
> > Instead, we can use VIRTIO_VSOCK_MAX_PKT_BUF_SIZE as the max
> > packet size.
> >
> > Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
>
>
> OK so this is kind of like GSO where we are passing
> 64K packets to the vsock and then split at the
> low level.
Exactly, something like that in the Host->Guest path, instead in the
Guest->Host we use the entire 64K packet.

Thanks,
Stefano

On Thu, Jul 18, 2019 at 09:52:41AM +0200, Stefano Garzarella
wrote:
> On Wed, Jul 17, 2019 at 5:00 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
> >
> > On Wed, Jul 17, 2019 at 01:30:30PM +0200, Stefano Garzarella wrote:
> > > Since now we are able to split packets, we can avoid limiting
> > > their sizes to VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE.
> > > Instead, we can use VIRTIO_VSOCK_MAX_PKT_BUF_SIZE as the max
> > > packet size.
> > >
> > > Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
> >
> >
> > OK so this is kind of like GSO where we are passing
> > 64K packets to the vsock and then split at the
> > low level.
> 
> Exactly, something like that in the Host->Guest path, instead in the
> Guest->Host we use the entire 64K packet.
> 
> Thanks,
> Stefano
btw two allocations for each packet isn't great. How about
allocating the struct linearly with the data?
And all buffers are same length for you - so you can actually
do alloc_pages.
Allocating/freeing pages in a batch should also be considered.

-- 
MST