Add a fast path in lock_sock_nested(), to avoid acquiring the socket spinlock only to set @owned to one: spin_lock_bh(&sk->sk_lock.slock); if (unlikely(sock_owned_by_user_nocheck(sk))) __lock_sock(sk); sk->sk_lock.owned = 1; spin_unlock_bh(&sk->sk_lock.slock); On x86_64 compiler generates something quite efficient: 00000000000077c0 : 77c0: f3 0f 1e fa endbr64 77c4: e8 00 00 00 00 call __fentry__ 77c9: b9 01 00 00 00 mov $0x1,%ecx 77ce: 31 c0 xor %eax,%eax 77d0: f0 48 0f b1 8f 48 01 00 00 lock cmpxchg %rcx,0x148(%rdi) 77d9: 75 06 jne slow_path 77db: 2e e9 00 00 00 00 cs jmp __x86_return_thunk-0x4 slow_path: ... Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima --- include/net/sock.h | 9 +++++++-- net/core/sock.c | 13 +++++++++++++ 2 files changed, 20 insertions(+), 2 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 55b61e4b0d8318887d527e919fc1103d78ac6d14..84c21fb38a28406e387dc33e0fb5decd18893950 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -81,8 +81,13 @@ * mini-semaphore synchronizes multiple users amongst themselves. */ typedef struct { - spinlock_t slock; - int owned; + union { + struct slock_owned { + int owned; + spinlock_t slock; + }; + long combined; + }; wait_queue_head_t wq; /* * We express the mutex-alike socket_lock semantics diff --git a/net/core/sock.c b/net/core/sock.c index cfb2a6209946089669882cdbd5d1b36c53838989..86185f194d64b4eea0835ee0f9b53fda184c73cb 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3780,6 +3780,19 @@ void noinline lock_sock_nested(struct sock *sk, int subclass) mutex_acquire(&sk->sk_lock.dep_map, subclass, 0, _RET_IP_); might_sleep(); +#ifdef CONFIG_64BIT + if (sizeof(struct slock_owned) == sizeof(long)) { + socket_lock_t tmp, old; + + tmp.slock = __SPIN_LOCK_UNLOCKED(tmp.slock); + tmp.owned = 1; + old.slock = __SPIN_LOCK_UNLOCKED(old.slock); + old.owned = 0; + if (likely(try_cmpxchg(&sk->sk_lock.combined, + &old.combined, tmp.combined))) + return; + } +#endif spin_lock_bh(&sk->sk_lock.slock); if (unlikely(sock_owned_by_user_nocheck(sk))) __lock_sock(sk); -- 2.53.0.414.gf7e9f6c205-goog