netdev - Re: [PATCH RFC 0/4] virtio-net: add tx-hash, rx-tstamp, tx-tstamp and tx-time

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Date: Wed, 20 Dec 2023 11:48:47 +0800
From: Jason Wang <jasowang@...hat.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Steffen Trumtrar <s.trumtrar@...gutronix.de>, "Michael S. Tsirkin" <mst@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Richard Cochran <richardcochran@...il.com>, virtualization@...ts.linux.dev, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RFC 0/4] virtio-net: add tx-hash, rx-tstamp, tx-tstamp and tx-time

On Tue, Dec 19, 2023 at 12:36 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Steffen Trumtrar wrote:
> > This series tries to pick up the work on the virtio-net timestamping
> > feature from Willem de Bruijn.
> >
> > Original series
> >     Message-Id: 20210208185558.995292-1-willemdebruijn.kernel@...il.com
> >     Subject: [PATCH RFC v2 0/4] virtio-net: add tx-hash, rx-tstamp,
> >     tx-tstamp and tx-time
> >     From: Willem de Bruijn <willemb@...gle.com>
> >
> >     RFC for four new features to the virtio network device:
> >
> >     1. pass tx flow state to host, for routing + telemetry
> >     2. pass rx tstamp to guest, for better RTT estimation
> >     3. pass tx tstamp to guest, idem
> >     3. pass tx delivery time to host, for accurate pacing
> >
> >     All would introduce an extension to the virtio spec.
> >
> > The original series consisted of a hack around the DMA API, which should
> > be fixed in this series.
> >
> > The changes in this series are to the driver side. For the changes to qemu see:
> >     https://github.com/strumtrar/qemu/tree/v8.1.1/virtio-net-ptp
> >
> > Currently only virtio-net is supported. The original series used
> > vhost-net as backend. However, the path through tun via sendmsg doesn't
> > allow us to write data back to the driver side without any hacks.
> > Therefore use the way via plain virtio-net without vhost albeit better
> > performance.
> >
> > Signed-off-by: Steffen Trumtrar <s.trumtrar@...gutronix.de>
>
> Thanks for picking this back up, Steffen. Nice to see that the code still
> applies mostly cleanly.
>
> For context: I dropped the work only because I had no real device
> implementation. The referenced patch series to qemu changes that.
>
> I suppose the main issue is the virtio API changes that this introduces,
> which will have to be accepted to the spec.
>
> One small comment to patch 4: there I just assumed the virtual device
> time is CLOCK_TAI. There is a concurrent feature under review for HW
> pacing offload with AF_XDP sockets. The clock issue comes up a bit. In
> general, for hardware we cannot assume a clock.

Any reason for this? E.g some modern NIC have PTP support.

> For virtio, perhaps
> assuming the same monotonic hardware clock in guest and host can be
> assumed.

Note that virtio can be implemented in hardware now. So we can assume
things like the kvm ptp clock.

> But this clock alignment needs some thought.
>

Thanks