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Date: Tue, 23 Aug 2016 07:47:32 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Netdev <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Alexander Duyck <alexander.h.duyck@...el.com>
Subject: Re: [PATCH net-next v1] gso: Support partial splitting at the
frag_list pointer
On Mon, Aug 22, 2016 at 10:20 PM, Steffen Klassert
<steffen.klassert@...unet.com> wrote:
> Since commit 8a29111c7 ("net: gro: allow to build full sized skb")
> gro may build buffers with a frag_list. This can hurt forwarding
> because most NICs can't offload such packets, they need to be
> segmented in software. This patch splits buffers with a frag_list
> at the frag_list pointer into buffers that can be TSO offloaded.
>
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
> net/core/skbuff.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++-
> net/ipv4/af_inet.c | 7 ++--
> net/ipv4/gre_offload.c | 7 +++-
> net/ipv4/tcp_offload.c | 3 ++
> net/ipv4/udp_offload.c | 9 +++--
> net/ipv6/ip6_offload.c | 6 +++-
> 6 files changed, 114 insertions(+), 7 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3864b4b6..a614e9d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3078,6 +3078,92 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
> sg = !!(features & NETIF_F_SG);
> csum = !!can_checksum_protocol(features, proto);
>
> + headroom = skb_headroom(head_skb);
> +
> + if (list_skb && net_gso_ok(features, skb_shinfo(head_skb)->gso_type) &&
> + csum && sg && (mss != GSO_BY_FRAGS) &&
> + !(features & NETIF_F_GSO_PARTIAL)) {
Does this really need to be mutually exclusive with
NETIF_F_GSO_PARTIAL and GSO_BY_FRAGS? This is occurring early enough
that maybe instead of doubling the size of skb_segment you should look
at instead adding a new static function that could handle splitting
the frag_list and just call that instead of adding this massive amount
of code.
Some of these checks are more expensive than others. I would
recommend doing the sg && csum && !(features & NETIF_F_GSO_PARTIAL)
checks first. If possible you could even combine some of the checks
since they are also in the block that sets up partial_segs. That way
we can cut down on the total number of conditional branches needed.
> + unsigned int lskb_segs;
> + unsigned int delta_segs, delta_len, delta_truesize;
> + struct sk_buff *nskb;
> + delta_segs = delta_len = delta_truesize = 0;
> +
> + segs = __alloc_skb(skb_headlen(head_skb) + headroom,
> + GFP_ATOMIC, skb_alloc_rx_flag(head_skb),
> + NUMA_NO_NODE);
> + if (unlikely(!segs))
> + return ERR_PTR(-ENOMEM);
> +
> + skb_reserve(segs, headroom);
> + skb_put(segs, skb_headlen(head_skb));
> + skb_copy_from_linear_data(head_skb, segs->data, segs->len);
> + copy_skb_header(segs, head_skb);
> +
> + if (skb_shinfo(head_skb)->nr_frags) {
> + int i;
> +
> + if (skb_orphan_frags(head_skb, GFP_ATOMIC))
> + goto err;
> +
> + for (i = 0; i < skb_shinfo(head_skb)->nr_frags; i++) {
> + skb_shinfo(segs)->frags[i] = skb_shinfo(head_skb)->frags[i];
> + skb_frag_ref(head_skb, i);
> + }
> + skb_shinfo(segs)->nr_frags = i;
> + }
> +
> + do {
> + nskb = skb_clone(list_skb, GFP_ATOMIC);
> + if (unlikely(!nskb))
> + goto err;
> +
> + list_skb = list_skb->next;
> +
> + if (!tail)
> + segs->next = nskb;
> + else
> + tail->next = nskb;
> +
> + tail = nskb;
> +
> + if (skb_cow_head(nskb, doffset + headroom))
> + goto err;
> +
> + lskb_segs = nskb->len / mss;
> +
> + skb_shinfo(nskb)->gso_size = mss;
> + skb_shinfo(nskb)->gso_type = skb_shinfo(head_skb)->gso_type;
> + skb_shinfo(nskb)->gso_segs = lskb_segs;
> +
> +
> + delta_segs += lskb_segs;
> + delta_len += nskb->len;
> + delta_truesize += nskb->truesize;
> +
> + __skb_push(nskb, doffset);
> +
> + skb_release_head_state(nskb);
> + __copy_skb_header(nskb, head_skb);
> +
> + skb_headers_offset_update(nskb, skb_headroom(nskb) - headroom);
> + skb_reset_mac_len(nskb);
> +
> + skb_copy_from_linear_data_offset(head_skb, -tnl_hlen,
> + nskb->data - tnl_hlen,
> + doffset + tnl_hlen);
> +
> + } while (list_skb);
> +
> + skb_shinfo(segs)->gso_segs -= delta_segs;
> + segs->len = head_skb->len - delta_len;
> + segs->data_len = head_skb->data_len - delta_len;
> + segs->truesize += head_skb->data_len - delta_truesize;
> +
> + segs->prev = tail;
> +
> + goto out;
> + }
> +
> /* 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.
> @@ -3090,7 +3176,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
> partial_segs = 0;
> }
>
> - headroom = skb_headroom(head_skb);
> pos = skb_headlen(head_skb);
>
> do {
> @@ -3307,6 +3392,8 @@ perform_csum_check:
> swap(tail->destructor, head_skb->destructor);
> swap(tail->sk, head_skb->sk);
> }
> +
> +out:
> return segs;
>
> err:
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 55513e6..c814afa 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1195,7 +1195,7 @@ EXPORT_SYMBOL(inet_sk_rebuild_header);
> struct sk_buff *inet_gso_segment(struct sk_buff *skb,
> netdev_features_t features)
> {
> - bool udpfrag = false, fixedid = false, encap;
> + bool udpfrag = false, fixedid = false, gso_partial = false, encap;
> struct sk_buff *segs = ERR_PTR(-EINVAL);
> const struct net_offload *ops;
> unsigned int offset = 0;
> @@ -1248,6 +1248,9 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
> if (IS_ERR_OR_NULL(segs))
> goto out;
>
> + if (skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL)
> + gso_partial = true;
> +
For these kind of blocks it is usually best to just do:
gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
The compiler usually does a better job of just doing a bit of
arithmetic instead of generating a set of test/jump type instructions
and generally that runs faster since there is less branching. The
same applies to all the other cases where you setup gso_partial this
way.
> skb = segs;
> do {
> iph = (struct iphdr *)(skb_mac_header(skb) + nhoff);
> @@ -1257,7 +1260,7 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
> iph->frag_off |= htons(IP_MF);
> offset += skb->len - nhoff - ihl;
> tot_len = skb->len - nhoff;
> - } else if (skb_is_gso(skb)) {
> + } else if (skb_is_gso(skb) && gso_partial) {
> if (!fixedid) {
> iph->id = htons(id);
> id += skb_shinfo(skb)->gso_segs;
> diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
> index ecd1e09..cf82e28 100644
> --- a/net/ipv4/gre_offload.c
> +++ b/net/ipv4/gre_offload.c
> @@ -24,7 +24,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
> __be16 protocol = skb->protocol;
> u16 mac_len = skb->mac_len;
> int gre_offset, outer_hlen;
> - bool need_csum, ufo;
> + bool need_csum, ufo, gso_partial;
>
> if (!skb->encapsulation)
> goto out;
> @@ -69,6 +69,11 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
> goto out;
> }
>
> + if (skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL)
> + gso_partial = true;
> + else
> + gso_partial = false;
> +
> outer_hlen = skb_tnl_header_len(skb);
> gre_offset = outer_hlen - tnl_hlen;
> skb = segs;
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 5c59649..dddd227 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -107,6 +107,9 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
>
> /* Only first segment might have ooo_okay set */
> segs->ooo_okay = ooo_okay;
> + if (skb_is_gso(segs) && !(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL))
> + mss = (skb_tail_pointer(segs) - skb_transport_header(segs)) +
> + segs->data_len - thlen;
>
> delta = htonl(oldlen + (thlen + mss));
>
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 81f253b..dfb6a2c 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -21,7 +21,7 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
> __be16 new_protocol, bool is_ipv6)
> {
> int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
> - bool remcsum, need_csum, offload_csum, ufo;
> + bool remcsum, need_csum, offload_csum, ufo, gso_partial;
> struct sk_buff *segs = ERR_PTR(-EINVAL);
> struct udphdr *uh = udp_hdr(skb);
> u16 mac_offset = skb->mac_header;
> @@ -88,6 +88,11 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
> goto out;
> }
>
> + if (skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL)
> + gso_partial = true;
> + else
> + gso_partial = false;
> +
> outer_hlen = skb_tnl_header_len(skb);
> udp_offset = outer_hlen - tnl_hlen;
> skb = segs;
> @@ -117,7 +122,7 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
> * will be using a length value equal to only one MSS sized
> * segment instead of the entire frame.
> */
> - if (skb_is_gso(skb)) {
> + if (skb_is_gso(skb) && gso_partial) {
> uh->len = htons(skb_shinfo(skb)->gso_size +
> SKB_GSO_CB(skb)->data_offset +
> skb->head - (unsigned char *)uh);
> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
> index 22e90e5..0ec16ba 100644
> --- a/net/ipv6/ip6_offload.c
> +++ b/net/ipv6/ip6_offload.c
> @@ -69,6 +69,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
> int offset = 0;
> bool encap, udpfrag;
> int nhoff;
> + bool gso_partial = false;
>
> skb_reset_network_header(skb);
> nhoff = skb_network_header(skb) - skb_mac_header(skb);
> @@ -101,9 +102,12 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
> if (IS_ERR(segs))
> goto out;
>
> + if (skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL)
> + gso_partial = true;
> +
> for (skb = segs; skb; skb = skb->next) {
> ipv6h = (struct ipv6hdr *)(skb_mac_header(skb) + nhoff);
> - if (skb_is_gso(skb))
> + if (skb_is_gso(skb) && gso_partial)
> payload_len = skb_shinfo(skb)->gso_size +
> SKB_GSO_CB(skb)->data_offset +
> skb->head - (unsigned char *)(ipv6h + 1);
> --
> 1.9.1
>
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