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Message-ID: <CANn89iJfVHA=n-vSpFwoP3Jb8Wxr1hgem1rLqmyPWPUwDpe-cg@mail.gmail.com>
Date: Tue, 7 May 2024 20:08:03 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Richard Gobert <richardbgobert@...il.com>
Cc: alexander.duyck@...il.com, davem@...emloft.net, dsahern@...nel.org,
kuba@...nel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, netdev@...r.kernel.org, pabeni@...hat.com,
shuah@...nel.org, willemdebruijn.kernel@...il.com
Subject: Re: [PATCH net-next v9 2/3] net: gro: move L3 flush checks to
tcp_gro_receive and udp_gro_receive_segment
On Tue, May 7, 2024 at 6:30 PM Richard Gobert <richardbgobert@...il.com> wrote:
>
> {inet,ipv6}_gro_receive functions perform flush checks (ttl, flags,
> iph->id, ...) against all packets in a loop. These flush checks are used in
> all merging UDP and TCP flows.
>
> These checks need to be done only once and only against the found p skb,
> since they only affect flush and not same_flow.
>
> This patch leverages correct network header offsets from the cb for both
> outer and inner network headers - allowing these checks to be done only
> once, in tcp_gro_receive and udp_gro_receive_segment. As a result,
> NAPI_GRO_CB(p)->flush is not used at all. In addition, flush_id checks are
> more declarative and contained in inet_gro_flush, thus removing the need
> for flush_id in napi_gro_cb.
>
> This results in less parsing code for non-loop flush tests for TCP and UDP
> flows.
>
> To make sure results are not within noise range - I've made netfilter drop
> all TCP packets, and measured CPU performance in GRO (in this case GRO is
> responsible for about 50% of the CPU utilization).
>
> perf top while replaying 64 parallel IP/TCP streams merging in GRO:
> (gro_receive_network_flush is compiled inline to tcp_gro_receive)
> net-next:
> 6.94% [kernel] [k] inet_gro_receive
> 3.02% [kernel] [k] tcp_gro_receive
>
> patch applied:
> 4.27% [kernel] [k] tcp_gro_receive
> 4.22% [kernel] [k] inet_gro_receive
>
> perf top while replaying 64 parallel IP/IP/TCP streams merging in GRO (same
> results for any encapsulation, in this case inet_gro_receive is top
> offender in net-next)
> net-next:
> 10.09% [kernel] [k] inet_gro_receive
> 2.08% [kernel] [k] tcp_gro_receive
>
> patch applied:
> 6.97% [kernel] [k] inet_gro_receive
> 3.68% [kernel] [k] tcp_gro_receive
>
> Signed-off-by: Richard Gobert <richardbgobert@...il.com>
> ---
> include/net/gro.h | 78 +++++++++++++++++++++++++++++++++++++-----
> net/core/gro.c | 3 --
> net/ipv4/af_inet.c | 41 +---------------------
> net/ipv4/tcp_offload.c | 17 ++-------
> net/ipv4/udp_offload.c | 10 ++----
> net/ipv6/ip6_offload.c | 11 ------
> 6 files changed, 76 insertions(+), 84 deletions(-)
>
> diff --git a/include/net/gro.h b/include/net/gro.h
> index 3dafa0f31ae1..e0939b4b6579 100644
> --- a/include/net/gro.h
> +++ b/include/net/gro.h
> @@ -36,15 +36,15 @@ struct napi_gro_cb {
> /* This is non-zero if the packet cannot be merged with the new skb. */
> u16 flush;
>
> - /* Save the IP ID here and check when we get to the transport layer */
> - u16 flush_id;
> -
> /* Number of segments aggregated. */
> u16 count;
>
> /* Used in ipv6_gro_receive() and foo-over-udp and esp-in-udp */
> u16 proto;
>
> + /* used to support CHECKSUM_COMPLETE for tunneling protocols */
> + __wsum csum;
> +
> /* Used in napi_gro_cb::free */
> #define NAPI_GRO_FREE 1
> #define NAPI_GRO_FREE_STOLEN_HEAD 2
> @@ -75,8 +75,8 @@ struct napi_gro_cb {
> /* Used in GRE, set in fou/gue_gro_receive */
> u8 is_fou:1;
>
> - /* Used to determine if flush_id can be ignored */
> - u8 is_atomic:1;
> + /* Used to determine if ipid_offset can be ignored */
> + u8 ip_fixedid:1;
>
> /* Number of gro_receive callbacks this packet already went through */
> u8 recursion_counter:4;
> @@ -85,9 +85,6 @@ struct napi_gro_cb {
> u8 is_flist:1;
> );
>
> - /* used to support CHECKSUM_COMPLETE for tunneling protocols */
> - __wsum csum;
> -
> /* L3 offsets */
> union {
> struct {
> @@ -442,6 +439,71 @@ static inline __wsum ip6_gro_compute_pseudo(const struct sk_buff *skb,
> skb_gro_len(skb), proto, 0));
> }
>
> +static inline int inet_gro_flush(const struct iphdr *iph, const struct iphdr *iph2,
> + struct sk_buff *p, bool outer)
> +{
> + 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 (outer && df)
> + return flush;
> +
> + /* 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;
> +
I could not find where NAPI_GRO_CB(p)->ip_fixedid was cleared, or initialized
if/when GRO is fed with a GRO/GSO packet.
> + if (NAPI_GRO_CB(p)->ip_fixedid && df)
> + return flush | ipid_offset;
> +
> + return flush | (ipid_offset ^ count);
> +}
> +
> +static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr *iph2)
> +{
> + /* <Version:4><Traffic_Class:8><Flow_Label:20> */
> + __be32 first_word = *(__be32 *)iph ^ *(__be32 *)iph2;
> +
> + /* Flush if Traffic Class fields are different. */
> + return !!((first_word & htonl(0x0FF00000)) |
> + (__force __be32)(iph->hop_limit ^ iph2->hop_limit));
> +}
> +
> +static inline int __gro_receive_network_flush(const void *th, const void *th2,
> + struct sk_buff *p, const u16 diff,
> + bool outer)
> +{
> + const void *nh = th - diff;
> + const void *nh2 = th2 - diff;
> +
> + if (((struct iphdr *)nh)->version == 6)
> + return ipv6_gro_flush(nh, nh2);
> + else
> + return inet_gro_flush(nh, nh2, p, outer);
> +}
> +
> +static inline int gro_receive_network_flush(const void *th, const void *th2,
> + struct sk_buff *p, int off)
> +{
> + const bool encap_mark = NAPI_GRO_CB(p)->encap_mark;
> + int flush;
> +
> + 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);
> +
> + return flush;
> +}
> +
> int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb);
>
> /* Pass the currently batched GRO_NORMAL SKBs up to the stack. */
> diff --git a/net/core/gro.c b/net/core/gro.c
> index 99a45a5211c9..3e9422c23bc9 100644
> --- a/net/core/gro.c
> +++ b/net/core/gro.c
> @@ -331,8 +331,6 @@ static void gro_list_prepare(const struct list_head *head,
> list_for_each_entry(p, head, list) {
> unsigned long diffs;
>
> - NAPI_GRO_CB(p)->flush = 0;
> -
> if (hash != skb_get_hash_raw(p)) {
> NAPI_GRO_CB(p)->same_flow = 0;
> continue;
> @@ -472,7 +470,6 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
> sizeof(u32))); /* Avoid slow unaligned acc */
> *(u32 *)&NAPI_GRO_CB(skb)->zeroed = 0;
> NAPI_GRO_CB(skb)->flush = skb_has_frag_list(skb);
> - NAPI_GRO_CB(skb)->is_atomic = 1;
> NAPI_GRO_CB(skb)->count = 1;
> if (unlikely(skb_is_gso(skb))) {
> NAPI_GRO_CB(skb)->count = skb_shinfo(skb)->gso_segs;
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 428196e1541f..44564d009e95 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1482,7 +1482,6 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
> struct sk_buff *p;
> unsigned int hlen;
> unsigned int off;
> - unsigned int id;
> int flush = 1;
> int proto;
>
> @@ -1508,13 +1507,10 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
> goto out;
>
> NAPI_GRO_CB(skb)->proto = proto;
> - id = ntohl(*(__be32 *)&iph->id);
> - flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (id & ~IP_DF));
> - id >>= 16;
> + flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (ntohl(*(__be32 *)&iph->id) & ~IP_DF));
>
> list_for_each_entry(p, head, list) {
> struct iphdr *iph2;
> - u16 flush_id;
>
> if (!NAPI_GRO_CB(p)->same_flow)
> continue;
> @@ -1531,43 +1527,8 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
> NAPI_GRO_CB(p)->same_flow = 0;
> continue;
> }
> -
> - /* All fields must match except length and checksum. */
> - NAPI_GRO_CB(p)->flush |=
> - (iph->ttl ^ iph2->ttl) |
> - (iph->tos ^ iph2->tos) |
> - ((iph->frag_off ^ iph2->frag_off) & htons(IP_DF));
> -
> - NAPI_GRO_CB(p)->flush |= flush;
> -
> - /* We need to store of the IP ID check to be included later
> - * when we can verify that this packet does in fact belong
> - * to a given flow.
> - */
> - flush_id = (u16)(id - ntohs(iph2->id));
> -
> - /* This bit of code makes it much easier for us to identify
> - * the cases where we are doing atomic vs non-atomic IP ID
> - * checks. Specifically an atomic check can return IP ID
> - * values 0 - 0xFFFF, while a non-atomic check can only
> - * return 0 or 0xFFFF.
> - */
> - if (!NAPI_GRO_CB(p)->is_atomic ||
> - !(iph->frag_off & htons(IP_DF))) {
> - flush_id ^= NAPI_GRO_CB(p)->count;
> - flush_id = flush_id ? 0xFFFF : 0;
> - }
> -
> - /* If the previous IP ID value was based on an atomic
> - * datagram we can overwrite the value and ignore it.
> - */
> - if (NAPI_GRO_CB(skb)->is_atomic)
> - NAPI_GRO_CB(p)->flush_id = flush_id;
> - else
> - NAPI_GRO_CB(p)->flush_id |= flush_id;
> }
>
> - NAPI_GRO_CB(skb)->is_atomic = !!(iph->frag_off & htons(IP_DF));
> NAPI_GRO_CB(skb)->flush |= flush;
> NAPI_GRO_CB(skb)->inner_network_offset = off;
>
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index b70ae50e658d..5f0af1338d62 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -232,9 +232,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb)
> goto out_check_final;
>
> found:
> - /* Include the IP ID check below from the inner most IP hdr */
> - flush = NAPI_GRO_CB(p)->flush;
> - flush |= (__force int)(flags & TCP_FLAG_CWR);
> + flush = (__force int)(flags & TCP_FLAG_CWR);
> flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
> ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
> flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
> @@ -242,16 +240,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb)
> flush |= *(u32 *)((u8 *)th + i) ^
> *(u32 *)((u8 *)th2 + i);
>
> - /* When we receive our second frame we can made a decision on if we
> - * continue this flow as an atomic flow with a fixed ID or if we use
> - * an incrementing ID.
> - */
> - if (NAPI_GRO_CB(p)->flush_id != 1 ||
> - NAPI_GRO_CB(p)->count != 1 ||
> - !NAPI_GRO_CB(p)->is_atomic)
> - flush |= NAPI_GRO_CB(p)->flush_id;
> - else
> - NAPI_GRO_CB(p)->is_atomic = false;
> + flush |= gro_receive_network_flush(th, th2, p, off);
>
> mss = skb_shinfo(p)->gso_size;
>
> @@ -338,7 +327,7 @@ INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
> iph->daddr, 0);
>
> skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4 |
> - (NAPI_GRO_CB(skb)->is_atomic * SKB_GSO_TCP_FIXEDID);
> + (NAPI_GRO_CB(skb)->ip_fixedid * SKB_GSO_TCP_FIXEDID);
>
> tcp_gro_complete(skb);
> return 0;
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 8721fe5beca2..726565159dc7 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -466,6 +466,7 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
> struct sk_buff *skb)
> {
> struct udphdr *uh = udp_gro_udphdr(skb);
> + int off = skb_gro_offset(skb);
> struct sk_buff *pp = NULL;
> struct udphdr *uh2;
> struct sk_buff *p;
> @@ -505,14 +506,7 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
> return p;
> }
>
> - flush = NAPI_GRO_CB(p)->flush;
> -
> - if (NAPI_GRO_CB(p)->flush_id != 1 ||
> - NAPI_GRO_CB(p)->count != 1 ||
> - !NAPI_GRO_CB(p)->is_atomic)
> - flush |= NAPI_GRO_CB(p)->flush_id;
> - else
> - NAPI_GRO_CB(p)->is_atomic = false;
> + flush = gro_receive_network_flush(uh, uh2, p, off);
>
> /* Terminate the flow on len mismatch or if it grow "too much".
> * Under small packet flood GRO count could elsewhere grow a lot
> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
> index 288c7c6ea50f..bd5aff97d8b1 100644
> --- a/net/ipv6/ip6_offload.c
> +++ b/net/ipv6/ip6_offload.c
> @@ -290,19 +290,8 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
> nlen - sizeof(struct ipv6hdr)))
> goto not_same_flow;
> }
> - /* flush if Traffic Class fields are different */
> - NAPI_GRO_CB(p)->flush |= !!((first_word & htonl(0x0FF00000)) |
> - (__force __be32)(iph->hop_limit ^ iph2->hop_limit));
> - NAPI_GRO_CB(p)->flush |= flush;
> -
> - /* If the previous IP ID value was based on an atomic
> - * datagram we can overwrite the value and ignore it.
> - */
> - if (NAPI_GRO_CB(skb)->is_atomic)
> - NAPI_GRO_CB(p)->flush_id = 0;
> }
>
> - NAPI_GRO_CB(skb)->is_atomic = true;
> NAPI_GRO_CB(skb)->flush |= flush;
>
> skb_gro_postpull_rcsum(skb, iph, nlen);
> --
> 2.36.1
>
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