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Date:   Mon, 28 Dec 2020 14:30:31 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        virtualization@...ts.linux-foundation.org,
        Network Development <netdev@...r.kernel.org>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH rfc 2/3] virtio-net: support receive timestamp

On Mon, Dec 28, 2020 at 12:29 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Mon, Dec 28, 2020 at 11:22:32AM -0500, Willem de Bruijn wrote:
> > From: Willem de Bruijn <willemb@...gle.com>
> >
> > Add optional PTP hardware timestamp offload for virtio-net.
> >
> > Accurate RTT measurement requires timestamps close to the wire.
> > Introduce virtio feature VIRTIO_NET_F_RX_TSTAMP. If negotiated, the
> > virtio-net header is expanded with room for a timestamp. A host may
> > pass receive timestamps for all or some packets. A timestamp is valid
> > if non-zero.
> >
> > The timestamp straddles (virtual) hardware domains. Like PTP, use
> > international atomic time (CLOCK_TAI) as global clock base. It is
> > guest responsibility to sync with host, e.g., through kvm-clock.
> >
> > Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> > diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> > index f6881b5b77ee..0ffe2eeebd4a 100644
> > --- a/include/uapi/linux/virtio_net.h
> > +++ b/include/uapi/linux/virtio_net.h
> > @@ -57,6 +57,7 @@
> >                                        * Steering */
> >  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23        /* Set MAC address */
> >
> > +#define VIRTIO_NET_F_RX_TSTAMP         55    /* Host sends TAI receive time */
> >  #define VIRTIO_NET_F_TX_HASH   56    /* Guest sends hash report */
> >  #define VIRTIO_NET_F_HASH_REPORT  57 /* Supports hash report */
> >  #define VIRTIO_NET_F_RSS       60    /* Supports RSS RX steering */
> > @@ -182,6 +183,17 @@ struct virtio_net_hdr_v1_hash {
> >       };
> >  };
> >
> > +struct virtio_net_hdr_v12 {
> > +     struct virtio_net_hdr_v1 hdr;
> > +     struct {
> > +             __le32 value;
> > +             __le16 report;
> > +             __le16 flow_state;
> > +     } hash;
> > +     __virtio32 reserved;
> > +     __virtio64 tstamp;
> > +};
> > +
> >  #ifndef VIRTIO_NET_NO_LEGACY
> >  /* This header comes first in the scatter-gather list.
> >   * For legacy virtio, if VIRTIO_F_ANY_LAYOUT is not negotiated, it must
>
>
> So it looks like VIRTIO_NET_F_RX_TSTAMP should depend on both
> VIRTIO_NET_F_RX_TSTAMP and VIRTIO_NET_F_HASH_REPORT then?

Do you mean VIRTIO_NET_F_TX_TSTAMP depends on VIRTIO_NET_F_RX_TSTAMP?

I think if either is enabled we need to enable the extended layout.
Regardless of whether TX_HASH or HASH_REPORT are enabled. If they are
not, then those fields are ignored.

> I am not sure what does v12 mean here.
>
> virtio_net_hdr_v1 is just with VIRTIO_F_VERSION_1,
> virtio_net_hdr_v1_hash is with VIRTIO_F_VERSION_1 and
> VIRTIO_NET_F_HASH_REPORT.
>
> So this one is virtio_net_hdr_hash_tstamp I guess?

Sounds better, yes, will change that.

This was an attempt at identifying the layout with the likely next
generation of the spec, 1.2. Similar to virtio_net_hdr_v1. But that is
both premature and not very helpful.

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