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net: avoid unconditionally touching sk_tsflags on RX

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After commit 5d4cc87414 ("net: reorganize "struct sock" fields"),
the sk_tsflags field shares the same cacheline with sk_forward_alloc.

The UDP protocol does not acquire the sock lock in the RX path;
forward allocations are protected via the receive queue spinlock;
additionally udp_recvmsg() calls sock_recv_cmsgs() unconditionally
touching sk_tsflags on each packet reception.

Due to the above, under high packet rate traffic, when the BH and the
user-space process run on different CPUs, UDP packet reception
experiences a cache miss while accessing sk_tsflags.

The receive path doesn't strictly need to access the problematic field;
change sock_set_timestamping() to maintain the relevant information
in a newly allocated sk_flags bit, so that sock_recv_cmsgs() can
take decisions accessing the latter field only.

With this patch applied, on an AMD epic server with i40e NICs, I
measured a 10% performance improvement for small packets UDP flood
performance tests - possibly a larger delta could be observed with more
recent H/W.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/dbd18c8a1171549f8249ac5a8b30b1b5ec88a425.1739294057.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2025-02-11 18:17:31 +01:00 committed by Jakub Kicinski
parent ea80f2d921
commit f0e70409b7
2 changed files with 6 additions and 4 deletions
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9
include/net/sock.h
View File

@ -954,6 +954,7 @@ enum sock_flags {
SOCK_TSTAMP_NEW, /* Indicates 64 bit timestamps always */
SOCK_RCVMARK, /* Receive SO_MARK ancillary data with packet */
SOCK_RCVPRIORITY, /* Receive SO_PRIORITY ancillary data with packet */
SOCK_TIMESTAMPING_ANY, /* Copy of sk_tsflags & TSFLAGS_ANY */
};
#define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))
@ -2664,13 +2665,13 @@ static inline void sock_recv_cmsgs(struct msghdr *msg, struct sock *sk,
{
#define FLAGS_RECV_CMSGS ((1UL << SOCK_RXQ_OVFL) | \
(1UL << SOCK_RCVTSTAMP) | \
(1UL << SOCK_RCVMARK) |\
(1UL << SOCK_RCVPRIORITY))
(1UL << SOCK_RCVMARK) | \
(1UL << SOCK_RCVPRIORITY) | \
(1UL << SOCK_TIMESTAMPING_ANY))
#define TSFLAGS_ANY (SOF_TIMESTAMPING_SOFTWARE | \
SOF_TIMESTAMPING_RAW_HARDWARE)
if (sk->sk_flags & FLAGS_RECV_CMSGS ||
READ_ONCE(sk->sk_tsflags) & TSFLAGS_ANY)
if (READ_ONCE(sk->sk_flags) & FLAGS_RECV_CMSGS)
__sock_recv_cmsgs(msg, sk, skb);
else if (unlikely(sock_flag(sk, SOCK_TIMESTAMP)))
sock_write_timestamp(sk, skb->tstamp);

1
net/core/sock.c
View File

@ -938,6 +938,7 @@ int sock_set_timestamping(struct sock *sk, int optname,
WRITE_ONCE(sk->sk_tsflags, val);
sock_valbool_flag(sk, SOCK_TSTAMP_NEW, optname == SO_TIMESTAMPING_NEW);
sock_valbool_flag(sk, SOCK_TIMESTAMPING_ANY, !!(val & TSFLAGS_ANY));
if (val & SOF_TIMESTAMPING_RX_SOFTWARE)
sock_enable_timestamp(sk,