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Date: Mon, 5 Sep 2016 10:30:44 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Netdev <netdev@...r.kernel.org>,
Alexander Duyck <alexander.h.duyck@...el.com>,
Eric Dumazet <eric.dumazet@...il.com>,
Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net-next v3] gso: Support partial splitting at the
frag_list pointer
On Mon, Sep 5, 2016 at 3:47 AM, 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>
> ---
>
> Changes since v1:
>
> - Use the assumption that all buffers in the chain excluding the last
> containing the same amount of data.
>
> - Simplify some checks against gso partial.
>
> - Fix the generation of IP IDs.
>
> Changes since v2:
>
> - Merge common code of gso partial and frag_list pointer splitting.
>
> net/core/skbuff.c | 50 +++++++++++++++++++++++++++++++++++++++-----------
> net/ipv4/af_inet.c | 14 ++++++++++----
> net/ipv4/gre_offload.c | 6 ++++--
> net/ipv4/tcp_offload.c | 13 +++++++------
> net/ipv4/udp_offload.c | 6 ++++--
> net/ipv6/ip6_offload.c | 5 ++++-
> 6 files changed, 68 insertions(+), 26 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3864b4b6..f754d47 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3078,11 +3078,30 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
> sg = !!(features & NETIF_F_SG);
> 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 (sg && csum && (features & NETIF_F_GSO_PARTIAL)) {
> + if (sg && csum && (mss != GSO_BY_FRAGS)) {
> + if (!(features & NETIF_F_GSO_PARTIAL)) {
> + if (list_skb &&
> + net_gso_ok(features, skb_shinfo(head_skb)->gso_type)) {
The testing logic here is a bit off.
You need to prevent us from doing the partial_segs bit below if
NETIF_F_GSO_PARTIAL is not set and if your list_skb or net_gso_ok
tests fail. Since as you pointed out we shouldn't ever be trying to
perform GSO_PARTIAL on a frame that has a frag_list, what you might do
is something like:
if (!list_skb || !net_gso_ok(...))
goto normal;
That way we don't setup partial_segs unless we are actually using it.
> + struct sk_buff *iter;
> +
> + /* Split the buffer at the frag_list pointer.
> + * This is based on the assumption that all
> + * buffers in the chain excluding the last
> + * containing the same amount of data.
> + */
> + skb_walk_frags(head_skb, iter) {
> + if (skb_headlen(iter))
> + goto normal;
> +
> + len -= iter->len;
> + }
> + }
> + }
> +
> + /* 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.
> + */
> partial_segs = len / mss;
> if (partial_segs > 1)
> mss *= partial_segs;
> @@ -3090,6 +3109,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
> partial_segs = 0;
> }
>
> +normal:
> headroom = skb_headroom(head_skb);
> pos = skb_headlen(head_skb);
>
> @@ -3281,21 +3301,29 @@ perform_csum_check:
> */
> segs->prev = tail;
>
> - /* Update GSO info on first skb in partial sequence. */
> if (partial_segs) {
> + struct sk_buff *iter;
> int type = skb_shinfo(head_skb)->gso_type;
> + unsigned short gso_size = skb_shinfo(head_skb)->gso_size;
>
> /* Update type to add partial and then remove dodgy if set */
> - type |= SKB_GSO_PARTIAL;
> + type |= (features & NETIF_F_GSO_PARTIAL) / NETIF_F_GSO_PARTIAL * SKB_GSO_PARTIAL;
> type &= ~SKB_GSO_DODGY;
>
> /* Update GSO info and prepare to start updating headers on
> * our way back down the stack of protocols.
> */
> - skb_shinfo(segs)->gso_size = skb_shinfo(head_skb)->gso_size;
> - skb_shinfo(segs)->gso_segs = partial_segs;
> - skb_shinfo(segs)->gso_type = type;
> - SKB_GSO_CB(segs)->data_offset = skb_headroom(segs) + doffset;
> + for (iter = segs; iter; iter = iter->next) {
> + skb_shinfo(iter)->gso_size = gso_size;
> + skb_shinfo(iter)->gso_segs = partial_segs;
> + skb_shinfo(iter)->gso_type = type;
> + SKB_GSO_CB(iter)->data_offset = skb_headroom(iter) + doffset;
> + }
> +
> + if (tail->len < gso_size)
You might swap this around and just setup gso_segs on > gso_size,
either that or this needs to be "<=" instead of just "<";
> + skb_shinfo(tail)->gso_size = 0;
> + else
> + skb_shinfo(tail)->gso_segs = DIV_ROUND_UP(tail->len, gso_size);
> }
>
> /* Following permits correct backpressure, for protocols
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index e94b47b..1effc98 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1192,7 +1192,7 @@ 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, encap;
> struct sk_buff *segs = ERR_PTR(-EINVAL);
> const struct net_offload *ops;
> unsigned int offset = 0;
> @@ -1245,6 +1245,8 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
> if (IS_ERR_OR_NULL(segs))
> goto out;
>
> + gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
> +
> skb = segs;
> do {
> iph = (struct iphdr *)(skb_mac_header(skb) + nhoff);
> @@ -1259,9 +1261,13 @@ struct sk_buff *inet_gso_segment(struct sk_buff *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;
> +
> + if (gso_partial)
> + tot_len = skb_shinfo(skb)->gso_size +
> + SKB_GSO_CB(skb)->data_offset +
> + skb->head - (unsigned char *)iph;
> + else
> + tot_len = skb->len - nhoff;
> } else {
> if (!fixedid)
> iph->id = htons(id++);
> diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
> index ecd1e09..96e0efe 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 +69,8 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
> goto out;
> }
>
> + gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
> +
> outer_hlen = skb_tnl_header_len(skb);
> gre_offset = outer_hlen - tnl_hlen;
> skb = segs;
> @@ -96,7 +98,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
> greh = (struct gre_base_hdr *)skb_transport_header(skb);
> pcsum = (__sum16 *)(greh + 1);
>
> - if (skb_is_gso(skb)) {
> + if (gso_partial) {
> unsigned int partial_adj;
>
> /* Adjust checksum to account for the fact that
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 5c59649..bc68da3 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -90,12 +90,6 @@ 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 */
> @@ -108,6 +102,13 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
> /* Only first segment might have ooo_okay set */
> segs->ooo_okay = ooo_okay;
>
> + /* GSO partial and frag_list segmentation only requires splitting
> + * the frame into an MSS multiple and possibly a remainder, both
> + * cases return a GSO skb. So update the mss now.
> + */
> + if (skb_is_gso(segs))
> + mss *= skb_shinfo(segs)->gso_segs;
> +
> delta = htonl(oldlen + (thlen + mss));
>
> skb = segs;
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 81f253b..f9333c9 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 +88,8 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
> goto out;
> }
>
> + gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
> +
> outer_hlen = skb_tnl_header_len(skb);
> udp_offset = outer_hlen - tnl_hlen;
> skb = segs;
> @@ -117,7 +119,7 @@ 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 (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..e7bfd55 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;
>
> skb_reset_network_header(skb);
> nhoff = skb_network_header(skb) - skb_mac_header(skb);
> @@ -101,9 +102,11 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
> if (IS_ERR(segs))
> goto out;
>
> + gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
> +
> for (skb = segs; skb; skb = skb->next) {
> ipv6h = (struct ipv6hdr *)(skb_mac_header(skb) + nhoff);
> - if (skb_is_gso(skb))
> + if (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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