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Date: Wed, 23 Mar 2016 10:09:47 -0700
From: Tom Herbert <tom@...bertland.com>
To: Alexander Duyck <aduyck@...antis.com>
Cc: Edward Cree <ecree@...arflare.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [RFC PATCH 7/9] GSO: Support partial segmentation offload
On Fri, Mar 18, 2016 at 4:25 PM, Alexander Duyck <aduyck@...antis.com> wrote:
> This patch adds support for something I am referring to as GSO partial.
> The basic idea is that we can support a broader range of devices for
> segmentation if we use fixed outer headers and have the hardware only
> really deal with segmenting the inner header. The idea behind the naming
> is due to the fact that everything before csum_start will be fixed headers,
> and everything after will be the region that is handled by hardware.
>
Personally, I don't like the name ;-) This technique should be
"generic" to handle almost all GSO except those case where headers are
not fixed which we should be able to avoid as a design point in any
new encapsulations. Besides, what if someday we perform GSO on
something where csum_start is not set?
Can you add some description about strategy for dealing with ip_id?
Thanks,
Tom
> With the current implementation it allows us to add support for the
> following GSO types with an inner TSO or TSO6 offload:
> NETIF_F_GSO_GRE
> NETIF_F_GSO_GRE_CSUM
> NETIF_F_UDP_TUNNEL
> NETIF_F_UDP_TUNNEL_CSUM
>
> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
> ---
> include/linux/netdev_features.h | 7 ++++++-
> include/linux/netdevice.h | 2 ++
> include/linux/skbuff.h | 7 ++++++-
> net/core/dev.c | 31 ++++++++++++++++++++++++++++++-
> net/core/ethtool.c | 1 +
> net/core/skbuff.c | 21 ++++++++++++++++++++-
> net/ipv4/af_inet.c | 12 ++++++++++--
> net/ipv4/gre_offload.c | 23 +++++++++++++++++++----
> net/ipv4/tcp_offload.c | 10 ++++++++--
> net/ipv4/udp_offload.c | 20 ++++++++++++++++----
> net/ipv6/ip6_offload.c | 9 ++++++++-
> 11 files changed, 126 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
> index a734bf43d190..8df3c5553af0 100644
> --- a/include/linux/netdev_features.h
> +++ b/include/linux/netdev_features.h
> @@ -48,8 +48,12 @@ enum {
> NETIF_F_GSO_UDP_TUNNEL_BIT, /* ... UDP TUNNEL with TSO */
> NETIF_F_GSO_UDP_TUNNEL_CSUM_BIT,/* ... UDP TUNNEL with TSO & CSUM */
> NETIF_F_GSO_TUNNEL_REMCSUM_BIT, /* ... TUNNEL with TSO & REMCSUM */
> + NETIF_F_GSO_PARTIAL_BIT, /* ... Only segment inner-most L4
> + * in hardware and all other
> + * headers in software.
> + */
> /**/NETIF_F_GSO_LAST = /* last bit, see GSO_MASK */
> - NETIF_F_GSO_TUNNEL_REMCSUM_BIT,
> + NETIF_F_GSO_PARTIAL_BIT,
>
> NETIF_F_FCOE_CRC_BIT, /* FCoE CRC32 */
> NETIF_F_SCTP_CRC_BIT, /* SCTP checksum offload */
> @@ -121,6 +125,7 @@ enum {
> #define NETIF_F_GSO_UDP_TUNNEL __NETIF_F(GSO_UDP_TUNNEL)
> #define NETIF_F_GSO_UDP_TUNNEL_CSUM __NETIF_F(GSO_UDP_TUNNEL_CSUM)
> #define NETIF_F_GSO_TUNNEL_REMCSUM __NETIF_F(GSO_TUNNEL_REMCSUM)
> +#define NETIF_F_GSO_PARTIAL __NETIF_F(GSO_PARTIAL)
> #define NETIF_F_HW_VLAN_STAG_FILTER __NETIF_F(HW_VLAN_STAG_FILTER)
> #define NETIF_F_HW_VLAN_STAG_RX __NETIF_F(HW_VLAN_STAG_RX)
> #define NETIF_F_HW_VLAN_STAG_TX __NETIF_F(HW_VLAN_STAG_TX)
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 31474d9d8a96..427d748ad8f9 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1647,6 +1647,7 @@ struct net_device {
> netdev_features_t vlan_features;
> netdev_features_t hw_enc_features;
> netdev_features_t mpls_features;
> + netdev_features_t gso_partial_features;
>
> int ifindex;
> int group;
> @@ -4014,6 +4015,7 @@ static inline bool net_gso_ok(netdev_features_t features, int gso_type)
> BUILD_BUG_ON(SKB_GSO_UDP_TUNNEL != (NETIF_F_GSO_UDP_TUNNEL >> NETIF_F_GSO_SHIFT));
> BUILD_BUG_ON(SKB_GSO_UDP_TUNNEL_CSUM != (NETIF_F_GSO_UDP_TUNNEL_CSUM >> NETIF_F_GSO_SHIFT));
> BUILD_BUG_ON(SKB_GSO_TUNNEL_REMCSUM != (NETIF_F_GSO_TUNNEL_REMCSUM >> NETIF_F_GSO_SHIFT));
> + BUILD_BUG_ON(SKB_GSO_PARTIAL != (NETIF_F_GSO_PARTIAL >> NETIF_F_GSO_SHIFT));
>
> return (features & feature) == feature;
> }
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 15d0df943466..c291a282f8b6 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -482,6 +482,8 @@ enum {
> SKB_GSO_UDP_TUNNEL_CSUM = 1 << 11,
>
> SKB_GSO_TUNNEL_REMCSUM = 1 << 12,
> +
> + SKB_GSO_PARTIAL = 1 << 13,
> };
>
> #if BITS_PER_LONG > 32
> @@ -3584,7 +3586,10 @@ static inline struct sec_path *skb_sec_path(struct sk_buff *skb)
> * Keeps track of level of encapsulation of network headers.
> */
> struct skb_gso_cb {
> - int mac_offset;
> + union {
> + int mac_offset;
> + int data_offset;
> + };
> int encap_level;
> __wsum csum;
> __u16 csum_start;
> diff --git a/net/core/dev.c b/net/core/dev.c
> index edb7179bc051..666cf427898b 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2711,6 +2711,19 @@ struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
> return ERR_PTR(err);
> }
>
> + /* Only report GSO partial support if it will enable us to
> + * support segmentation on this frame without needing additional
> + * work.
> + */
> + if (features & NETIF_F_GSO_PARTIAL) {
> + netdev_features_t partial_features;
> + struct net_device *dev = skb->dev;
> +
> + partial_features = dev->features & dev->gso_partial_features;
> + if (!skb_gso_ok(skb, features | partial_features))
> + features &= ~NETIF_F_GSO_PARTIAL;
> + }
> +
> BUILD_BUG_ON(SKB_SGO_CB_OFFSET +
> sizeof(*SKB_GSO_CB(skb)) > sizeof(skb->cb));
>
> @@ -2841,6 +2854,14 @@ netdev_features_t netif_skb_features(struct sk_buff *skb)
> if (skb->encapsulation)
> features &= dev->hw_enc_features;
>
> + /* Support for GSO partial features requires software intervention
> + * before we can actually process the packets so we need to strip
> + * support for any partial features now and we can pull them back
> + * in after we have partially segmented the frame.
> + */
> + if (skb_is_gso(skb) && !(skb_shinfo(skb)->gso_type & SKB_GSO_PARTIAL))
> + features &= ~dev->gso_partial_features;
> +
> if (skb_vlan_tagged(skb))
> features = netdev_intersect_features(features,
> dev->vlan_features |
> @@ -6702,6 +6723,14 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
> }
> }
>
> + /* GSO partial features require GSO partial be set */
> + if ((features & dev->gso_partial_features) &&
> + !(features & NETIF_F_GSO_PARTIAL)) {
> + netdev_dbg(dev,
> + "Dropping partially supported GSO features since no GSO partial.\n");
> + features &= ~dev->gso_partial_features;
> + }
> +
> #ifdef CONFIG_NET_RX_BUSY_POLL
> if (dev->netdev_ops->ndo_busy_poll)
> features |= NETIF_F_BUSY_POLL;
> @@ -6982,7 +7011,7 @@ int register_netdevice(struct net_device *dev)
>
> /* Make NETIF_F_SG inheritable to tunnel devices.
> */
> - dev->hw_enc_features |= NETIF_F_SG;
> + dev->hw_enc_features |= NETIF_F_SG | NETIF_F_GSO_PARTIAL;
>
> /* Make NETIF_F_SG inheritable to MPLS.
> */
> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index b3c39d531469..d1b278c6c29f 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
> @@ -88,6 +88,7 @@ static const char netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN]
> [NETIF_F_GSO_UDP_TUNNEL_BIT] = "tx-udp_tnl-segmentation",
> [NETIF_F_GSO_UDP_TUNNEL_CSUM_BIT] = "tx-udp_tnl-csum-segmentation",
> [NETIF_F_GSO_TUNNEL_REMCSUM_BIT] = "tx-remcsum-segmentation",
> + [NETIF_F_GSO_PARTIAL_BIT] = "tx-gso-partial",
>
> [NETIF_F_FCOE_CRC_BIT] = "tx-checksum-fcoe-crc",
> [NETIF_F_SCTP_CRC_BIT] = "tx-checksum-sctp",
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index f044f970f1a6..bdcba77e164c 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3076,8 +3076,9 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
> struct sk_buff *frag_skb = head_skb;
> unsigned int offset = doffset;
> unsigned int tnl_hlen = skb_tnl_header_len(head_skb);
> + unsigned int partial_segs = 0;
> unsigned int headroom;
> - unsigned int len;
> + unsigned int len = head_skb->len;
> __be16 proto;
> bool csum;
> int sg = !!(features & NETIF_F_SG);
> @@ -3094,6 +3095,15 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
>
> csum = !!can_checksum_protocol(features, proto);
>
> + /* GSO partial only requires that we trim off any excess that
> + * doesn't fit into an MSS sized block, so take care of that
> + * now.
> + */
> + if (features & NETIF_F_GSO_PARTIAL) {
> + partial_segs = len / mss;
> + mss *= partial_segs;
> + }
> +
> headroom = skb_headroom(head_skb);
> pos = skb_headlen(head_skb);
>
> @@ -3281,6 +3291,15 @@ perform_csum_check:
> */
> segs->prev = tail;
>
> + /* Update GSO info on first skb in partial sequence. */
> + if (partial_segs) {
> + skb_shinfo(segs)->gso_size = mss / partial_segs;
> + skb_shinfo(segs)->gso_segs = partial_segs;
> + skb_shinfo(segs)->gso_type = skb_shinfo(head_skb)->gso_type |
> + SKB_GSO_PARTIAL;
> + SKB_GSO_CB(segs)->data_offset = skb_headroom(segs) + doffset;
> + }
> +
> /* Following permits correct backpressure, for protocols
> * using skb_set_owner_w().
> * Idea is to tranfert ownership from head_skb to last segment.
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 5e3885672907..d091f91fa25d 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1199,7 +1199,7 @@ static struct sk_buff *inet_gso_segment(struct sk_buff *skb,
> unsigned int offset = 0;
> bool udpfrag, encap;
> struct iphdr *iph;
> - int proto;
> + int proto, tot_len;
> int nhoff;
> int ihl;
> int id;
> @@ -1269,10 +1269,18 @@ static struct sk_buff *inet_gso_segment(struct sk_buff *skb,
> if (skb->next)
> iph->frag_off |= htons(IP_MF);
> offset += skb->len - nhoff - ihl;
> + tot_len = skb->len - nhoff;
> + } else if (skb_is_gso(skb)) {
> + iph->id = htons(id);
> + id += skb_shinfo(skb)->gso_segs;
> + tot_len = skb_shinfo(skb)->gso_size +
> + SKB_GSO_CB(skb)->data_offset +
> + skb->head - (unsigned char *)iph;
> } else {
> iph->id = htons(id++);
> + tot_len = skb->len - nhoff;
> }
> - iph->tot_len = htons(skb->len - nhoff);
> + iph->tot_len = htons(tot_len);
> ip_send_check(iph);
> if (encap)
> skb_reset_inner_headers(skb);
> diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
> index 7ea14ced9222..dea0390d65bb 100644
> --- a/net/ipv4/gre_offload.c
> +++ b/net/ipv4/gre_offload.c
> @@ -85,7 +85,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
> skb = segs;
> do {
> struct gre_base_hdr *greh;
> - __be32 *pcsum;
> + __sum16 *pcsum;
>
> /* Set up inner headers if we are offloading inner checksum */
> if (skb->ip_summed == CHECKSUM_PARTIAL) {
> @@ -105,10 +105,25 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
> continue;
>
> greh = (struct gre_base_hdr *)skb_transport_header(skb);
> - pcsum = (__be32 *)(greh + 1);
> + pcsum = (__sum16 *)(greh + 1);
> +
> + if (skb_is_gso(skb)) {
> + unsigned int partial_adj;
> +
> + /* Adjust checksum to account for the fact that
> + * the partial checksum is based on actual size
> + * whereas headers should be based on MSS size.
> + */
> + partial_adj = skb->len + skb_headroom(skb) -
> + SKB_GSO_CB(skb)->data_offset -
> + skb_shinfo(skb)->gso_size;
> + *pcsum = ~csum_fold((__force __wsum)htonl(partial_adj));
> + } else {
> + *pcsum = 0;
> + }
>
> - *pcsum = 0;
> - *(__sum16 *)pcsum = gso_make_checksum(skb, 0);
> + *(pcsum + 1) = 0;
> + *pcsum = gso_make_checksum(skb, 0);
> } while ((skb = skb->next));
> out:
> return segs;
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 1a2e9957c177..4e9b8f011473 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -107,6 +107,12 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
> goto out;
> }
>
> + /* GSO partial only requires splitting the frame into an MSS
> + * multiple and possibly a remainder. So update the mss now.
> + */
> + if (features & NETIF_F_GSO_PARTIAL)
> + mss = skb->len - (skb->len % mss);
> +
> copy_destructor = gso_skb->destructor == tcp_wfree;
> ooo_okay = gso_skb->ooo_okay;
> /* All segments but the first should have ooo_okay cleared */
> @@ -131,7 +137,7 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
> newcheck = ~csum_fold((__force __wsum)((__force u32)th->check +
> (__force u32)delta));
>
> - do {
> + while (skb->next) {
> th->fin = th->psh = 0;
> th->check = newcheck;
>
> @@ -151,7 +157,7 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
>
> th->seq = htonl(seq);
> th->cwr = 0;
> - } while (skb->next);
> + }
>
> /* Following permits TCP Small Queues to work well with GSO :
> * The callback to TCP stack will be called at the time last frag
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 8a3405a80260..5fcb93269afb 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -100,7 +100,7 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
> udp_offset = outer_hlen - tnl_hlen;
> skb = segs;
> do {
> - __be16 len;
> + unsigned int len;
>
> if (remcsum)
> skb->ip_summed = CHECKSUM_NONE;
> @@ -118,14 +118,26 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
> skb_reset_mac_header(skb);
> skb_set_network_header(skb, mac_len);
> skb_set_transport_header(skb, udp_offset);
> - len = htons(skb->len - udp_offset);
> + len = skb->len - udp_offset;
> uh = udp_hdr(skb);
> - uh->len = len;
> +
> + /* If we are only performing partial GSO the inner header
> + * will be using a length value equal to only one MSS sized
> + * segment instead of the entire frame.
> + */
> + if (skb_is_gso(skb)) {
> + uh->len = htons(skb_shinfo(skb)->gso_size +
> + SKB_GSO_CB(skb)->data_offset +
> + skb->head - (unsigned char *)uh);
> + } else {
> + uh->len = htons(len);
> + }
>
> if (!need_csum)
> continue;
>
> - uh->check = ~csum_fold(csum_add(partial, (__force __wsum)len));
> + uh->check = ~csum_fold(csum_add(partial,
> + (__force __wsum)htonl(len)));
>
> if (skb->encapsulation || !offload_csum) {
> uh->check = gso_make_checksum(skb, ~uh->check);
> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
> index eeca943f12dc..d467053c226a 100644
> --- a/net/ipv6/ip6_offload.c
> +++ b/net/ipv6/ip6_offload.c
> @@ -63,6 +63,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
> int proto;
> struct frag_hdr *fptr;
> unsigned int unfrag_ip6hlen;
> + unsigned int payload_len;
> u8 *prevhdr;
> int offset = 0;
> bool encap, udpfrag;
> @@ -117,7 +118,13 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
>
> for (skb = segs; skb; skb = skb->next) {
> ipv6h = (struct ipv6hdr *)(skb_mac_header(skb) + nhoff);
> - ipv6h->payload_len = htons(skb->len - nhoff - sizeof(*ipv6h));
> + if (skb_is_gso(skb))
> + payload_len = skb_shinfo(skb)->gso_size +
> + SKB_GSO_CB(skb)->data_offset +
> + skb->head - (unsigned char *)(ipv6h + 1);
> + else
> + payload_len = skb->len - nhoff - sizeof(*ipv6h);
> + ipv6h->payload_len = htons(payload_len);
> skb->network_header = (u8 *)ipv6h - skb->head;
>
> if (udpfrag) {
>
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