netdev - Re: [PATCH v2 0/5] VSOCK: support mergeable rx buffer in vhost-vsock

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Message-ID: <20181213163409.GP23318@stefanha-x1.localdomain>
Date:   Thu, 13 Dec 2018 16:34:09 +0000
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     jiangyiwen <jiangyiwen@...wei.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 0/5] VSOCK: support mergeable rx buffer in vhost-vsock

On Wed, Dec 12, 2018 at 05:25:50PM +0800, jiangyiwen wrote:
> Now vsock only support send/receive small packet, it can't achieve
> high performance. As previous discussed with Jason Wang, I revisit the
> idea of vhost-net about mergeable rx buffer and implement the mergeable
> rx buffer in vhost-vsock, it can allow big packet to be scattered in
> into different buffers and improve performance obviously.

Sorry, I've been a bad maintainer.  I was focussed on other projects and
my email backlog is huge.

I like the idea of trying out optimizations on virtio-vsock, seeing if
code can be shared with virtio-net, and maybe later switching to a
virtio-net transport for vsock (if it turns out enough code can be
shared).

Another optimization that could be interesting:

Userspace processes reading from a socket sleep in
vsock_stream_recvmsg().  I wonder if we can bypass struct
virtio_vsock_pkt and copying the payload into pkt->buf in this case.
(This doesn't improve poll(2)/select(2) though!)

Imagine a userspace process waiting for data on a socket.  When the
virtqueue becomes ready, we can read in struct virtio_vsock_hdr and find
the socket for that connection.  Then we could copy the payload directly
to userspace instead of creating a virtio_vsock_pkt and copying to
pkt->buf first.

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