Linux Virtualization - Apr 2019 - [PATCH RFC 0/4] vsock/virtio: optimizations to increase the throughput

On Thu, Apr 04, 2019 at 02:04:10PM -0400, Michael S. Tsirkin
wrote:
> On Thu, Apr 04, 2019 at 06:47:15PM +0200, Stefano Garzarella wrote:
> > On Thu, Apr 04, 2019 at 11:52:46AM -0400, Michael S. Tsirkin wrote:
> > > I simply love it that you have analysed the individual impact of
> > > each patch! Great job!
> > 
> > Thanks! I followed Stefan's suggestions!
> > 
> > > 
> > > For comparison's sake, it could be IMHO benefitial to add a
column
> > > with virtio-net+vhost-net performance.
> > > 
> > > This will both give us an idea about whether the vsock layer
introduces
> > > inefficiencies, and whether the virtio-net idea has merit.
> > > 
> > 
> > Sure, I already did TCP tests on virtio-net + vhost, starting qemu in
> > this way:
> >   $ qemu-system-x86_64 ... \
> >       -netdev tap,id=net0,vhost=on,ifname=tap0,script=no,downscript=no
\
> >       -device virtio-net-pci,netdev=net0
> > 
> > I did also a test using TCP_NODELAY, just to be fair, because VSOCK
> > doesn't implement something like this.
> 
> Why not?
> 
I think because originally VSOCK was designed to be simple and
low-latency, but of course we can introduce something like that.

Current implementation directly copy the buffer from the user-space in a
virtio_vsock_pkt and enqueue it to be transmitted.

Maybe we can introduce a buffer per socket where accumulate bytes and
send it when it is full or when a timer is fired . We can also introduce
a VSOCK_NODELAY (maybe using the same value of TCP_NODELAY for
compatibility) to send the buffer immediately for low-latency use cases.

What do you think?

Thanks,
Stefano

On Fri, Apr 05, 2019 at 09:49:17AM +0200, Stefano Garzarella
wrote:
> On Thu, Apr 04, 2019 at 02:04:10PM -0400, Michael S. Tsirkin wrote:
> > On Thu, Apr 04, 2019 at 06:47:15PM +0200, Stefano Garzarella wrote:
> > > On Thu, Apr 04, 2019 at 11:52:46AM -0400, Michael S. Tsirkin
wrote:
> > > > I simply love it that you have analysed the individual
impact of
> > > > each patch! Great job!
> > > 
> > > Thanks! I followed Stefan's suggestions!
> > > 
> > > > 
> > > > For comparison's sake, it could be IMHO benefitial to
add a column
> > > > with virtio-net+vhost-net performance.
> > > > 
> > > > This will both give us an idea about whether the vsock layer
introduces
> > > > inefficiencies, and whether the virtio-net idea has merit.
> > > > 
> > > 
> > > Sure, I already did TCP tests on virtio-net + vhost, starting
qemu in
> > > this way:
> > >   $ qemu-system-x86_64 ... \
> > >       -netdev
tap,id=net0,vhost=on,ifname=tap0,script=no,downscript=no \
> > >       -device virtio-net-pci,netdev=net0
> > > 
> > > I did also a test using TCP_NODELAY, just to be fair, because
VSOCK
> > > doesn't implement something like this.
> > 
> > Why not?
> > 
> 
> I think because originally VSOCK was designed to be simple and
> low-latency, but of course we can introduce something like that.
> 
> Current implementation directly copy the buffer from the user-space in a
> virtio_vsock_pkt and enqueue it to be transmitted.
> 
> Maybe we can introduce a buffer per socket where accumulate bytes and
> send it when it is full or when a timer is fired . We can also introduce
> a VSOCK_NODELAY (maybe using the same value of TCP_NODELAY for
> compatibility) to send the buffer immediately for low-latency use cases.
> 
> What do you think?
Today virtio-vsock implements a 1:1 sendmsg():packet relationship
because it's simple.  But there's no need for the guest to enqueue
multiple VIRTIO_VSOCK_OP_RW packets when a single large packet could
combine all payloads for a connection.  This is not the same as
TCP_NODELAY but related.

I think it's worth exploring TCP_NODELAY and send_pkt_list merging.
Hopefully it won't make the code much more complicated.

Stefan
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