linux-kernel - Re: [PATCH RFC 0/4] vsock/virtio: optimizations to increase the throughput

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Date:   Fri, 5 Apr 2019 09:49:17 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [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