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Message-ID: <CAKH8qBtQf9g8Ye7QZ5+s2j+srJEkBwy3GAXPwPaxVeoc056C_A@mail.gmail.com>
Date: Fri, 15 Sep 2023 09:25:11 -0700
From: Stanislav Fomichev <sdf@...gle.com>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org, yhs@...com,
john.fastabend@...il.com, kpsingh@...nel.org, haoluo@...gle.com,
jolsa@...nel.org, kuba@...nel.org, toke@...nel.org, willemb@...gle.com,
dsahern@...nel.org, magnus.karlsson@...el.com, bjorn@...nel.org,
maciej.fijalkowski@...el.com, hawk@...nel.org, yoong.siang.song@...el.com,
netdev@...r.kernel.org, xdp-hints@...-project.net
Subject: Re: [PATCH bpf-next v2 2/9] xsk: add TX timestamp and TX checksum
offload support
On Thu, Sep 14, 2023 at 6:30 PM Vinicius Costa Gomes
<vinicius.gomes@...el.com> wrote:
>
> Hi,
>
> Stanislav Fomichev <sdf@...gle.com> writes:
>
> > This change actually defines the (initial) metadata layout
> > that should be used by AF_XDP userspace (xsk_tx_metadata).
> > The first field is flags which requests appropriate offloads,
> > followed by the offload-specific fields. The supported per-device
> > offloads are exported via netlink (new xsk-flags).
> >
> > The offloads themselves are still implemented in a bit of a
> > framework-y fashion that's left from my initial kfunc attempt.
> > I'm introducing new xsk_tx_metadata_ops which drivers are
> > supposed to implement. The drivers are also supposed
> > to call xsk_tx_metadata_request/xsk_tx_metadata_complete in
> > the right places. Since xsk_tx_metadata_{request,_complete}
> > are static inline, we don't incur any extra overhead doing
> > indirect calls.
> >
> > The benefit of this scheme is as follows:
> > - keeps all metadata layout parsing away from driver code
> > - makes it easy to grep and see which drivers implement what
> > - don't need any extra flags to maintain to keep track of what
> > offloads are implemented; if the callback is implemented - the offload
> > is supported (used by netlink reporting code)
> >
> > Two offloads are defined right now:
> > 1. XDP_TX_METADATA_CHECKSUM: skb-style csum_start+csum_offset
> > 2. XDP_TX_METADATA_TIMESTAMP: writes TX timestamp back into metadata
> > area upon completion (tx_timestamp field)
> >
> > The offloads are also implemented for copy mode:
> > 1. Extra XDP_TX_METADATA_CHECKSUM_SW to trigger skb_checksum_help; this
> > might be useful as a reference implementation and for testing
> > 2. XDP_TX_METADATA_TIMESTAMP writes SW timestamp from the skb
> > destructor (note I'm reusing hwtstamps to pass metadata pointer)
> >
> > The struct is forward-compatible and can be extended in the future
> > by appending more fields.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> > Documentation/netlink/specs/netdev.yaml | 20 +++++++
> > include/linux/netdevice.h | 27 +++++++++
> > include/linux/skbuff.h | 14 ++++-
> > include/net/xdp_sock.h | 80 +++++++++++++++++++++++++
> > include/net/xdp_sock_drv.h | 13 ++++
> > include/net/xsk_buff_pool.h | 6 ++
> > include/uapi/linux/if_xdp.h | 40 +++++++++++++
> > include/uapi/linux/netdev.h | 16 +++++
> > net/core/netdev-genl.c | 12 +++-
> > net/xdp/xsk.c | 39 ++++++++++++
> > net/xdp/xsk_queue.h | 2 +-
> > tools/include/uapi/linux/if_xdp.h | 54 +++++++++++++++--
> > tools/include/uapi/linux/netdev.h | 15 +++++
> > 13 files changed, 330 insertions(+), 8 deletions(-)
> >
> > diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> > index 1c7284fd535b..9002b37b7676 100644
> > --- a/Documentation/netlink/specs/netdev.yaml
> > +++ b/Documentation/netlink/specs/netdev.yaml
> > @@ -42,6 +42,19 @@ name: netdev
> > doc:
> > This feature informs if netdev implements non-linear XDP buffer
> > support in ndo_xdp_xmit callback.
> > + -
> > + type: flags
> > + name: xsk-flags
> > + render-max: true
> > + entries:
> > + -
> > + name: tx-timestamp
> > + doc:
> > + HW timestamping egress packets is supported by the driver.
> > + -
> > + name: tx-checksum
> > + doc:
> > + L3 checksum HW offload is supported by the driver.
> >
> > attribute-sets:
> > -
> > @@ -68,6 +81,12 @@ name: netdev
> > type: u32
> > checks:
> > min: 1
> > + -
> > + name: xsk-features
> > + doc: Bitmask of enabled AF_XDP features.
> > + type: u64
> > + enum: xsk-flags
> > + enum-as-flags: true
> >
> > operations:
> > list:
> > @@ -84,6 +103,7 @@ name: netdev
> > - ifindex
> > - xdp-features
> > - xdp-zc-max-segs
> > + - xsk-features
> > dump:
> > reply: *dev-all
> > -
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 0896aaa91dd7..3f02aaa30590 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -1647,6 +1647,31 @@ struct net_device_ops {
> > struct netlink_ext_ack *extack);
> > };
> >
> > +/*
> > + * This structure defines the AF_XDP TX metadata hooks for network devices.
> > + * The following hooks can be defined; unless noted otherwise, they are
> > + * optional and can be filled with a null pointer.
> > + *
> > + * int (*tmo_request_timestamp)(void *priv)
> > + * This function is called when AF_XDP frame requested egress timestamp.
> > + *
> > + * int (*tmo_fill_timestamp)(void *priv)
> > + * This function is called when AF_XDP frame, that had requested
> > + * egress timestamp, received a completion. The hook needs to return
> > + * the actual HW timestamp.
> > + *
> > + * int (*tmo_request_checksum)(u16 csum_start, u16 csum_offset, void *priv)
> > + * This function is called when AF_XDP frame requested HW checksum
> > + * offload. csum_start indicates position where checksumming should start.
> > + * csum_offset indicates position where checksum should be stored.
> > + *
> > + */
> > +struct xsk_tx_metadata_ops {
> > + void (*tmo_request_timestamp)(void *priv);
> > + u64 (*tmo_fill_timestamp)(void *priv);
> > + void (*tmo_request_checksum)(u16 csum_start, u16 csum_offset, void *priv);
> > +};
> > +
> > /**
> > * enum netdev_priv_flags - &struct net_device priv_flags
> > *
> > @@ -1835,6 +1860,7 @@ enum netdev_ml_priv_type {
> > * @netdev_ops: Includes several pointers to callbacks,
> > * if one wants to override the ndo_*() functions
> > * @xdp_metadata_ops: Includes pointers to XDP metadata callbacks.
> > + * @xsk_tx_metadata_ops: Includes pointers to AF_XDP TX metadata callbacks.
> > * @ethtool_ops: Management operations
> > * @l3mdev_ops: Layer 3 master device operations
> > * @ndisc_ops: Includes callbacks for different IPv6 neighbour
> > @@ -2091,6 +2117,7 @@ struct net_device {
> > unsigned long long priv_flags;
> > const struct net_device_ops *netdev_ops;
> > const struct xdp_metadata_ops *xdp_metadata_ops;
> > + const struct xsk_tx_metadata_ops *xsk_tx_metadata_ops;
> > int ifindex;
> > unsigned short gflags;
> > unsigned short hard_header_len;
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 4174c4b82d13..444d35dcd690 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -566,6 +566,15 @@ struct ubuf_info_msgzc {
> > int mm_account_pinned_pages(struct mmpin *mmp, size_t size);
> > void mm_unaccount_pinned_pages(struct mmpin *mmp);
> >
> > +/* Preserve some data across TX submission and completion.
> > + *
> > + * Note, this state is stored in the driver. Extending the layout
> > + * might need some special care.
> > + */
> > +struct xsk_tx_metadata_compl {
> > + __u64 *tx_timestamp;
> > +};
> > +
> > /* This data is invariant across clones and lives at
> > * the end of the header data, ie. at skb->end.
> > */
> > @@ -578,7 +587,10 @@ struct skb_shared_info {
> > /* Warning: this field is not always filled in (UFO)! */
> > unsigned short gso_segs;
> > struct sk_buff *frag_list;
> > - struct skb_shared_hwtstamps hwtstamps;
> > + union {
> > + struct skb_shared_hwtstamps hwtstamps;
> > + struct xsk_tx_metadata_compl xsk_meta;
> > + };
> > unsigned int gso_type;
> > u32 tskey;
> >
> > diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> > index 10993a05d220..c438c614a8d0 100644
> > --- a/include/net/xdp_sock.h
> > +++ b/include/net/xdp_sock.h
> > @@ -90,6 +90,74 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
> > int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp);
> > void __xsk_map_flush(void);
> >
> > +/**
> > + * xsk_tx_metadata_to_compl - Save enough relevant metadata information
> > + * to perform tx completion in the future.
> > + * @meta: pointer to AF_XDP metadata area
> > + * @compl: pointer to output struct xsk_tx_metadata_to_compl
> > + *
> > + * This function should be called by the networking device when
> > + * it prepares AF_XDP egress packet. The value of @compl should be stored
> > + * and passed to xsk_tx_metadata_complete upon TX completion.
> > + */
> > +static inline void xsk_tx_metadata_to_compl(struct xsk_tx_metadata *meta,
> > + struct xsk_tx_metadata_compl *compl)
>
> One of my systems didn't have the config XDP_SOCKETS enabled, and found
> some issues:
>
> This function is not defined when XDP_SOCKETS is disabled, got a
> compilation error.
>
> > +{
> > + if (!meta)
> > + return;
> > +
> > + if (meta->flags & XDP_TX_METADATA_TIMESTAMP)
> > + compl->tx_timestamp = &meta->completion.tx_timestamp;
> > + else
> > + compl->tx_timestamp = NULL;
> > +}
> > +
> > +/**
> > + * xsk_tx_metadata_request - Evaluate AF_XDP TX metadata at submission
> > + * and call appropriate xsk_tx_metadata_ops operation.
> > + * @meta: pointer to AF_XDP metadata area
> > + * @ops: pointer to struct xsk_tx_metadata_ops
> > + * @priv: pointer to driver-private aread
> > + *
> > + * This function should be called by the networking device when
> > + * it prepares AF_XDP egress packet.
> > + */
> > +static inline void xsk_tx_metadata_request(const struct xsk_tx_metadata *meta,
> > + const struct xsk_tx_metadata_ops *ops,
> > + void *priv)
> > +{
> > + if (!meta)
> > + return;
> > +
> > + if (ops->tmo_request_timestamp)
> > + if (meta->flags & XDP_TX_METADATA_TIMESTAMP)
> > + ops->tmo_request_timestamp(priv);
> > +
> > + if (ops->tmo_request_checksum)
> > + if (meta->flags & XDP_TX_METADATA_CHECKSUM)
> > + ops->tmo_request_checksum(meta->csum_start, meta->csum_offset, priv);
> > +}
> > +
> > +/**
> > + * xsk_tx_metadata_complete - Evaluate AF_XDP TX metadata at completion
> > + * and call appropriate xsk_tx_metadata_ops operation.
> > + * @compl: pointer to completion metadata produced from xsk_tx_metadata_to_compl
> > + * @ops: pointer to struct xsk_tx_metadata_ops
> > + * @priv: pointer to driver-private aread
> > + *
> > + * This function should be called by the networking device upon
> > + * AF_XDP egress completion.
> > + */
> > +static inline void xsk_tx_metadata_complete(struct xsk_tx_metadata_compl *compl,
> > + const struct xsk_tx_metadata_ops *ops,
> > + void *priv)
> > +{
> > + if (!compl)
> > + return;
> > +
> > + *compl->tx_timestamp = ops->tmo_fill_timestamp(priv);
> > +}
> > +
> > #else
> >
> > static inline int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
> > @@ -106,6 +174,18 @@ static inline void __xsk_map_flush(void)
> > {
> > }
> >
> > +static inline void xsk_tx_metadata_request(struct xsk_tx_metadata *meta,
> > + const struct xsk_tx_metadata_ops *ops,
> > + void *priv)
> > +{
> > +}
> > +
> > +static inline void xsk_tx_metadata_complete(struct xsk_tx_metadata_comp *compl,
>
> typo here: should be 'struct xsk_tx_metadata_compl'.
>
> Just so you are aware of these (very) minor issues for the next version.
>
> I enabled XDP_SOCKETS and will take a better look.
Thank you, will take a look. There are a bunch of bot build errors
that look similar as well.
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