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Message-ID: <65807512bc20b_805482941e@willemb.c.googlers.com.notmuch>
Date: Mon, 18 Dec 2023 11:36:34 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Steffen Trumtrar <s.trumtrar@...gutronix.de>,
"Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...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>
Cc: 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
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. For virtio, perhaps
assuming the same monotonic hardware clock in guest and host can be
assumed. But this clock alignment needs some thought.
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