From 73a6bab5aa2a83cb7df85805e08bc03b4065aea7 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 10 May 2018 14:59:43 -0700 Subject: tcp: switch pacing timer to softirq based hrtimer linux-4.16 got support for softirq based hrtimers. TCP can switch its pacing hrtimer to this variant, since this avoids going through a tasklet and some atomic operations. pacing timer logic looks like other (jiffies based) tcp timers. v2: use hrtimer_try_to_cancel() in tcp_clear_xmit_timers() to correctly release reference on socket if needed. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/tcp.h | 4 ++- net/ipv4/tcp_output.c | 69 +++++++++++++++++++-------------------------------- net/ipv4/tcp_timer.c | 2 +- 3 files changed, 29 insertions(+), 46 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index cf803fe0fb86..3b1d617b0110 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -557,7 +557,9 @@ void tcp_fin(struct sock *sk); void tcp_init_xmit_timers(struct sock *); static inline void tcp_clear_xmit_timers(struct sock *sk) { - hrtimer_cancel(&tcp_sk(sk)->pacing_timer); + if (hrtimer_try_to_cancel(&tcp_sk(sk)->pacing_timer) == 1) + sock_put(sk); + inet_csk_clear_xmit_timers(sk); } diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index d07c0dcc99aa..0d8f950a9006 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -772,7 +772,7 @@ struct tsq_tasklet { }; static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet); -static void tcp_tsq_handler(struct sock *sk) +static void tcp_tsq_write(struct sock *sk) { if ((1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING | @@ -789,6 +789,16 @@ static void tcp_tsq_handler(struct sock *sk) 0, GFP_ATOMIC); } } + +static void tcp_tsq_handler(struct sock *sk) +{ + bh_lock_sock(sk); + if (!sock_owned_by_user(sk)) + tcp_tsq_write(sk); + else if (!test_and_set_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) + sock_hold(sk); + bh_unlock_sock(sk); +} /* * One tasklet per cpu tries to send more skbs. * We run in tasklet context but need to disable irqs when @@ -816,16 +826,7 @@ static void tcp_tasklet_func(unsigned long data) smp_mb__before_atomic(); clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags); - if (!sk->sk_lock.owned && - test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) { - bh_lock_sock(sk); - if (!sock_owned_by_user(sk)) { - clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags); - tcp_tsq_handler(sk); - } - bh_unlock_sock(sk); - } - + tcp_tsq_handler(sk); sk_free(sk); } } @@ -853,9 +854,10 @@ void tcp_release_cb(struct sock *sk) nflags = flags & ~TCP_DEFERRED_ALL; } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags); - if (flags & TCPF_TSQ_DEFERRED) - tcp_tsq_handler(sk); - + if (flags & TCPF_TSQ_DEFERRED) { + tcp_tsq_write(sk); + __sock_put(sk); + } /* Here begins the tricky part : * We are called from release_sock() with : * 1) BH disabled @@ -929,7 +931,7 @@ void tcp_wfree(struct sk_buff *skb) if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED)) goto out; - nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED; + nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED; nval = cmpxchg(&sk->sk_tsq_flags, oval, nval); if (nval != oval) continue; @@ -948,37 +950,17 @@ out: sk_free(sk); } -/* Note: Called under hard irq. - * We can not call TCP stack right away. +/* Note: Called under soft irq. + * We can call TCP stack right away, unless socket is owned by user. */ enum hrtimer_restart tcp_pace_kick(struct hrtimer *timer) { struct tcp_sock *tp = container_of(timer, struct tcp_sock, pacing_timer); struct sock *sk = (struct sock *)tp; - unsigned long nval, oval; - for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) { - struct tsq_tasklet *tsq; - bool empty; + tcp_tsq_handler(sk); + sock_put(sk); - if (oval & TSQF_QUEUED) - break; - - nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED; - nval = cmpxchg(&sk->sk_tsq_flags, oval, nval); - if (nval != oval) - continue; - - if (!refcount_inc_not_zero(&sk->sk_wmem_alloc)) - break; - /* queue this socket to tasklet queue */ - tsq = this_cpu_ptr(&tsq_tasklet); - empty = list_empty(&tsq->head); - list_add(&tp->tsq_node, &tsq->head); - if (empty) - tasklet_schedule(&tsq->tasklet); - break; - } return HRTIMER_NORESTART; } @@ -1011,7 +993,8 @@ static void tcp_internal_pacing(struct sock *sk, const struct sk_buff *skb) do_div(len_ns, rate); hrtimer_start(&tcp_sk(sk)->pacing_timer, ktime_add_ns(ktime_get(), len_ns), - HRTIMER_MODE_ABS_PINNED); + HRTIMER_MODE_ABS_PINNED_SOFT); + sock_hold(sk); } static void tcp_update_skb_after_send(struct tcp_sock *tp, struct sk_buff *skb) @@ -1078,7 +1061,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, /* if no packet is in qdisc/device queue, then allow XPS to select * another queue. We can be called from tcp_tsq_handler() - * which holds one reference to sk_wmem_alloc. + * which holds one reference to sk. * * TODO: Ideally, in-flight pure ACK packets should not matter here. * One way to get this would be to set skb->truesize = 2 on them. @@ -2185,7 +2168,7 @@ static int tcp_mtu_probe(struct sock *sk) static bool tcp_pacing_check(const struct sock *sk) { return tcp_needs_internal_pacing(sk) && - hrtimer_active(&tcp_sk(sk)->pacing_timer); + hrtimer_is_queued(&tcp_sk(sk)->pacing_timer); } /* TCP Small Queues : @@ -2365,8 +2348,6 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, skb, limit, mss_now, gfp))) break; - if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) - clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags); if (tcp_small_queue_check(sk, skb, 0)) break; diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index f7d944855f8e..92bdf64fffae 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -713,6 +713,6 @@ void tcp_init_xmit_timers(struct sock *sk) inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, &tcp_keepalive_timer); hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC, - HRTIMER_MODE_ABS_PINNED); + HRTIMER_MODE_ABS_PINNED_SOFT); tcp_sk(sk)->pacing_timer.function = tcp_pace_kick; } -- cgit v1.2.3-59-g8ed1b