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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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2018-05-10 14:59:43 -07:00 committed by David S. Miller
parent 4cbd7a7d3c
commit 73a6bab5aa
3 changed files with 29 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/net/tcp.h
View File

@ -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);
}

69
net/ipv4/tcp_output.c
View File

@ -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;

2
net/ipv4/tcp_timer.c
View File

@ -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;
}