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net: gro: move L3 flush checks to tcp_gro_receive and udp_gro_receive_segment 

{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@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20240509190819.2985-3-richardbgobert@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Richard Gobert 2024-05-09 21:08:18 +02:00 committed by Jakub Kicinski
parent 186b1ea73a
commit 4b0ebbca3e
6 changed files with 73 additions and 84 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

76
include/net/gro.h
View File

@ -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 +439,69 @@ 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 (flush | (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;
return ipid_offset ^ (count * !NAPI_GRO_CB(p)->ip_fixedid);
}
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)
{
const bool encap_mark = NAPI_GRO_CB(p)->encap_mark;
int off = skb_transport_offset(p);
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);
int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb);

3
net/core/gro.c
View File

@ -358,8 +358,6 @@ 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;
@ -499,7 +497,6 @@ found_ptype:
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;

41
net/ipv4/af_inet.c
View File

@ -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;

17
net/ipv4/tcp_offload.c
View File

@ -313,10 +313,8 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb,
if (!p)
goto out_check_final;
/* Include the IP ID check below from the inner most IP hdr */
th2 = tcp_hdr(p);
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);
@ -324,16 +322,7 @@ 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);
mss = skb_shinfo(p)->gso_size;
@ -480,7 +469,7 @@ 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;

9
net/ipv4/udp_offload.c
View File

@ -478,14 +478,7 @@ 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);
/* Terminate the flow on len mismatch or if it grow "too much".
* Under small packet flood GRO count could elsewhere grow a lot

11
net/ipv6/ip6_offload.c
View File

@ -290,19 +290,8 @@ not_same_flow:
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);