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Date: Wed, 31 Aug 2016 10:25:59 -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 v2] gso: Support partial splitting at the
frag_list pointer
On Wed, Aug 31, 2016 at 3:41 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.
>
> net/core/skbuff.c | 56 +++++++++++++++++++++++++++++++++++++++++---------
> 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, 75 insertions(+), 25 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3864b4b6..67fa1a9 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3060,6 +3060,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
> unsigned int offset = doffset;
> unsigned int tnl_hlen = skb_tnl_header_len(head_skb);
> unsigned int partial_segs = 0;
> + unsigned int fraglist_segs = 0;
> unsigned int headroom;
> unsigned int len = head_skb->len;
> __be16 proto;
> @@ -3078,18 +3079,40 @@ 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)) {
> - partial_segs = len / mss;
> - if (partial_segs > 1)
> - mss *= partial_segs;
> - else
> - partial_segs = 0;
> + if (sg && csum) {
Actually you could also put the && (mss != GSO_BY_FRAGS) test up here
as well. The GSO_PARTIAL code doesn't make any sense if we are
segmenting by frags.
> + /* 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;
> + if (partial_segs > 1)
> + mss *= partial_segs;
> + else
> + partial_segs = 0;
> + } else if (list_skb && (mss != GSO_BY_FRAGS) &&
> + net_gso_ok(features, skb_shinfo(head_skb)->gso_type)) {
> + struct sk_buff *iter;
Actually I think we have the ordering backwards here by a little bit.
What we should probably be doing is your test for list_skb and such
first and then checking for GSO_PARTIAL. If I am not mistaken we
could end up with a situation where we have buffers with a frag_list
that need to be partially segmented. Also I think we can merge
partial_segs and fraglist_segs into one thing.
> +
> + /* 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;
> + }
What you could probably do here is actually have a goto that jumps
into the code for NETIF_F_GSO_PARTIAL. If we do that then these two
paths are mostly merged.
> + fraglist_segs = len / mss;
> + if (fraglist_segs > 1)
> + mss *= fraglist_segs;
> + else
> + fraglist_segs = 0;
> + }
> }
>
> +normal:
> headroom = skb_headroom(head_skb);
> pos = skb_headlen(head_skb);
>
So one bit I can think of that might be an issue if we have to do both
this and GSO_PARTIAL is that we might end up with a last chunk that
has to be segmented twice, once to get rid of frag_list and again to
trim the end piece off so that we are are evenly MSS aligned. To
resolve that you will need to tweak one piece inside of the main
segmenting loop related to mss:
if (unlikely(mss == GSO_BY_FRAGS)) {
len = list_skb->len;
} else {
len = head_skb->len - offset;
if (len > mss) {
len = mss;
} else if (partial_segs &
(features & NETIF_F_GSO_PARTIAL)) {
unsigned int gso_size =
skb_shinfo(head_skb)->gso_size;
if (len > gso_size)
len = (len / gso_size) * gso_size;
}
}
> @@ -3298,6 +3321,19 @@ perform_csum_check:
> SKB_GSO_CB(segs)->data_offset = skb_headroom(segs) + doffset;
> }
>
> + if (fraglist_segs) {
> + struct sk_buff *iter;
> +
> + for (iter = segs; iter; iter = iter->next) {
> + skb_shinfo(iter)->gso_size = skb_shinfo(head_skb)->gso_size;
> +
> + if (iter->next)
> + skb_shinfo(iter)->gso_segs = fraglist_segs;
> + else
> + skb_shinfo(iter)->gso_segs = iter->len / skb_shinfo(head_skb)->gso_size;
It might be faster to just set gso_segs to fraglist_segs in every
iteration of the loop, and then outside of the loop you could update
the tail skb. It will save the effort of a test and jump which should
be a few cycles per iteration. Also you will probably need to fixup
gso_size for the tail segment. If the length less than or equal to
gso_size then you need to drop gso_size to 0, otherwise you update
gso_segs. Also I am pretty sure you will want to use a DIV_ROUND_UP
logic for the segments since you want to reflect the actual packet
count.
Also this is still doing the same thing as I do at the end of the loop
in the conditional section for partial segs. What we may want to do
is just tweak the bits I have in that block with a check that is
something along the lines of:
/* Update type to add partial and then remove dodgy if set */
type |= (features & NETIF_F_GSO_PARTIAL) /
NETIF_F_GSO_PARTIAL * SKB_GSO_PARTIAL;
type &= ~SKB_GSO_DODGY;
That bit of code is just a fancy way of setting the SKB_GSO_PARTIAL
bit only if the NETIF_F_GSO_PARTIAL feature bit is set. Since we can
avoid conditional jumps that way it usually runs faster since it is
just an AND, SHIFT, and OR and I don't have any CPU flags to worry
about. Once you have type recorded you could just set the 4 values I
do in your loop and then fixup the last one.
> + }
> + }
> +
> /* 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 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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