Willem de Bruijn
2020-Dec-29 01:05 UTC
[PATCH rfc 2/3] virtio-net: support receive timestamp
On Mon, Dec 28, 2020 at 7:55 PM Michael S. Tsirkin <mst at redhat.com> wrote:> > On Mon, Dec 28, 2020 at 02:30:31PM -0500, Willem de Bruijn wrote: > > On Mon, Dec 28, 2020 at 12:29 PM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > > > On Mon, Dec 28, 2020 at 11:22:32AM -0500, Willem de Bruijn wrote: > > > > From: Willem de Bruijn <willemb at google.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 at google.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 mean do we waste the 8 bytes for hash if TSTAMP is set but HASH is not? > If TSTAMP depends on HASH then point is moot.True, but the two features really are independent. I did consider using configurable metadata layout depending on features negotiated. If there are tons of optional extensions, that makes sense. But it is more complex and parsing error prone. With a handful of options each of a few bytes, that did not seem worth the cost to me at this point. And importantly, such a mode can always be added later as a separate VIRTIO_NET_F_PACKED_HEADER option. If anything, perhaps if we increase the virtio_net_hdr_* allocation, we should allocate some additional reserved space now? As each new size introduces quite a bit of boilerplate. Also, e.g., in qemu just to pass the sizes between virtio-net driver and vhost-net device.
----- Original Message -----> On Mon, Dec 28, 2020 at 7:55 PM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > On Mon, Dec 28, 2020 at 02:30:31PM -0500, Willem de Bruijn wrote: > > > On Mon, Dec 28, 2020 at 12:29 PM Michael S. Tsirkin <mst at redhat.com> > > > wrote: > > > > > > > > On Mon, Dec 28, 2020 at 11:22:32AM -0500, Willem de Bruijn wrote: > > > > > From: Willem de Bruijn <willemb at google.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 at google.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 mean do we waste the 8 bytes for hash if TSTAMP is set but HASH is not? > > If TSTAMP depends on HASH then point is moot. > > True, but the two features really are independent. > > I did consider using configurable metadata layout depending on > features negotiated. If there are tons of optional extensions, that > makes sense. But it is more complex and parsing error prone. With a > handful of options each of a few bytes, that did not seem worth the > cost to me at this point.Consider NFV workloads(64B) packet. Most fields of current vnet header is even a burdern. It might be the time to introduce configurable or self-descriptive vnet header.> > And importantly, such a mode can always be added later as a separate > VIRTIO_NET_F_PACKED_HEADER option.What will do feature provide? Thanks> > If anything, perhaps if we increase the virtio_net_hdr_* allocation, > we should allocate some additional reserved space now? As each new > size introduces quite a bit of boilerplate. Also, e.g., in qemu just > to pass the sizes between virtio-net driver and vhost-net device. > >