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Message-ID: <willemdebruijn.kernel.277f254610c6e@gmail.com>
Date: Tue, 02 Sep 2025 14:08:34 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Richard Gobert <richardbgobert@...il.com>,
netdev@...r.kernel.org
Cc: davem@...emloft.net,
edumazet@...gle.com,
kuba@...nel.org,
pabeni@...hat.com,
horms@...nel.org,
corbet@....net,
saeedm@...dia.com,
tariqt@...dia.com,
mbloch@...dia.com,
leon@...nel.org,
ecree.xilinx@...il.com,
dsahern@...nel.org,
ncardwell@...gle.com,
kuniyu@...gle.com,
shuah@...nel.org,
sdf@...ichev.me,
aleksander.lobakin@...el.com,
florian.fainelli@...adcom.com,
willemdebruijn.kernel@...il.com,
alexander.duyck@...il.com,
linux-kernel@...r.kernel.org,
linux-net-drivers@....com,
Richard Gobert <richardbgobert@...il.com>
Subject: Re: [PATCH net-next v4 2/5] net: gro: only merge packets with
incrementing or fixed outer ids
Richard Gobert wrote:
> Only merge encapsulated packets if their outer IDs are either
> incrementing or fixed, just like for inner IDs and IDs of non-encapsulated
> packets.
>
> Add another ip_fixedid bit for a total of two bits: one for outer IDs (and
> for unencapsulated packets) and one for inner IDs.
>
> This commit preserves the current behavior of GSO where only the IDs of the
> inner-most headers are restored correctly.
>
> Signed-off-by: Richard Gobert <richardbgobert@...il.com>
> ---
> include/net/gro.h | 30 +++++++++++++++---------------
> net/ipv4/tcp_offload.c | 5 ++++-
> 2 files changed, 19 insertions(+), 16 deletions(-)
>
> diff --git a/include/net/gro.h b/include/net/gro.h
> index 87c68007f949..322c5517f508 100644
> --- a/include/net/gro.h
> +++ b/include/net/gro.h
> @@ -75,7 +75,7 @@ struct napi_gro_cb {
> u8 is_fou:1;
>
> /* Used to determine if ipid_offset can be ignored */
> - u8 ip_fixedid:1;
> + u8 ip_fixedid:2;
>
> /* Number of gro_receive callbacks this packet already went through */
> u8 recursion_counter:4;
> @@ -442,29 +442,26 @@ static inline __wsum ip6_gro_compute_pseudo(const struct sk_buff *skb,
> }
>
> static inline int inet_gro_flush(const struct iphdr *iph, const struct iphdr *iph2,
> - struct sk_buff *p, bool outer)
> + struct sk_buff *p, bool inner)
> {
> const u32 id = ntohl(*(__be32 *)&iph->id);
> const u32 id2 = ntohl(*(__be32 *)&iph2->id);
> const u16 ipid_offset = (id >> 16) - (id2 >> 16);
> const u16 count = NAPI_GRO_CB(p)->count;
> const u32 df = id & IP_DF;
> - int flush;
>
> /* All fields must match except length and checksum. */
> - flush = (iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF));
> -
> - if (flush | (outer && df))
> - return flush;
> + if ((iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF)))
> + return true;
>
> /* When we receive our second frame we can make a decision on if we
> * continue this flow as an atomic flow with a fixed ID or if we use
> * an incrementing ID.
> */
> if (count == 1 && df && !ipid_offset)
> - NAPI_GRO_CB(p)->ip_fixedid = true;
> + NAPI_GRO_CB(p)->ip_fixedid |= 1 << inner;
>
> - return ipid_offset ^ (count * !NAPI_GRO_CB(p)->ip_fixedid);
> + return ipid_offset ^ (count * !(NAPI_GRO_CB(p)->ip_fixedid & (1 << inner)));
> }
>
> static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr *iph2)
> @@ -479,7 +476,7 @@ static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr
>
> static inline int __gro_receive_network_flush(const void *th, const void *th2,
> struct sk_buff *p, const u16 diff,
> - bool outer)
> + bool inner)
> {
> const void *nh = th - diff;
> const void *nh2 = th2 - diff;
> @@ -487,19 +484,22 @@ static inline int __gro_receive_network_flush(const void *th, const void *th2,
> if (((struct iphdr *)nh)->version == 6)
> return ipv6_gro_flush(nh, nh2);
> else
> - return inet_gro_flush(nh, nh2, p, outer);
> + return inet_gro_flush(nh, nh2, p, inner);
> }
>
> static inline int gro_receive_network_flush(const void *th, const void *th2,
> struct sk_buff *p)
> {
> - const bool encap_mark = NAPI_GRO_CB(p)->encap_mark;
> int off = skb_transport_offset(p);
> int flush;
> + int diff;
>
> - flush = __gro_receive_network_flush(th, th2, p, off - NAPI_GRO_CB(p)->network_offset, encap_mark);
> - if (encap_mark)
> - flush |= __gro_receive_network_flush(th, th2, p, off - NAPI_GRO_CB(p)->inner_network_offset, false);
> + diff = off - NAPI_GRO_CB(p)->network_offset;
> + flush = __gro_receive_network_flush(th, th2, p, diff, false);
> + if (NAPI_GRO_CB(p)->encap_mark) {
> + diff = off - NAPI_GRO_CB(p)->inner_network_offset;
> + flush |= __gro_receive_network_flush(th, th2, p, diff, true);
> + }
nit: this diff introduction is not needed. The patch is easier to
parse without the change. Even if line length will (still) be longer.
>
> return flush;
> }
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index e6612bd84d09..1949eede9ec9 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -471,6 +471,7 @@ INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
> const u16 offset = NAPI_GRO_CB(skb)->network_offsets[skb->encapsulation];
> const struct iphdr *iph = (struct iphdr *)(skb->data + offset);
> struct tcphdr *th = tcp_hdr(skb);
> + bool is_fixedid;
>
> if (unlikely(NAPI_GRO_CB(skb)->is_flist)) {
> skb_shinfo(skb)->gso_type |= SKB_GSO_FRAGLIST | SKB_GSO_TCPV4;
> @@ -484,8 +485,10 @@ INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
> th->check = ~tcp_v4_check(skb->len - thoff, iph->saddr,
> iph->daddr, 0);
>
> + is_fixedid = (NAPI_GRO_CB(skb)->ip_fixedid >> skb->encapsulation) & 1;
> +
> skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4 |
> - (NAPI_GRO_CB(skb)->ip_fixedid * SKB_GSO_TCP_FIXEDID);
> + (is_fixedid * SKB_GSO_TCP_FIXEDID);
Similar to how gro_receive_network_flush is called from both transport
layers, TCP and UDP, this is needed in udp_gro_complete_segment too?
Existing equivalent block is entirely missing there.
The deeper issue is that this is named TCP_FIXEDID, but in reality it
is IPV4_FIXEDID and applies to all transport layer protocols on top.
Perhaps not to fix in this series. But a limitation of USO in the
meantime.
>
> tcp_gro_complete(skb);
> return 0;
> --
> 2.36.1
>
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