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Date: Fri, 20 Jul 2012 17:45:50 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>, Tom Herbert <therbert@...gle.com>,
Yuchung Cheng <ycheng@...gle.com>,
Neal Cardwell <ncardwell@...gle.com>,
Nandita Dukkipati <nanditad@...gle.com>,
John Heffner <johnwheffner@...il.com>,
"H.K. Jerry Chu" <hkchu@...gle.com>
Subject: [PATCH net-next] tcp: improve latencies of timer triggered events
From: Eric Dumazet <edumazet@...gle.com>
Modern TCP stack highly depends on tcp_write_timer() having a small
latency, but current implementation doesn't exactly meet the
expectations.
When a timer fires but finds the socket is owned by the user, it rearms
itself for an additional delay hoping next run will be more
successful.
tcp_write_timer() for example uses a 50ms delay for next try, and it
defeats many attempts to get predictable TCP behavior in term of
latencies.
Use the recently introduced tcp_release_cb(), so that the user owning
the socket will call various handlers right before socket release.
This will permit us to post a followup patch to address the
tcp_tso_should_defer() syndrome (some deferred packets have to wait
RTO timer to be transmitted, while cwnd should allow us to send them
sooner)
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Tom Herbert <therbert@...gle.com>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
Cc: Nandita Dukkipati <nanditad@...gle.com>
Cc: H.K. Jerry Chu <hkchu@...gle.com>
Cc: John Heffner <johnwheffner@...il.com>
---
include/linux/tcp.h | 4 +-
include/net/tcp.h | 2 +
net/ipv4/tcp_output.c | 46 ++++++++++++++++----------
net/ipv4/tcp_timer.c | 70 +++++++++++++++++++++-------------------
4 files changed, 71 insertions(+), 51 deletions(-)
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 9febfb6..2761856 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -515,7 +515,9 @@ struct tcp_sock {
enum tsq_flags {
TSQ_THROTTLED,
TSQ_QUEUED,
- TSQ_OWNED, /* tcp_tasklet_func() found socket was locked */
+ TCP_TSQ_DEFERRED, /* tcp_tasklet_func() found socket was owned */
+ TCP_WRITE_TIMER_DEFERRED, /* tcp_write_timer() found socket was owned */
+ TCP_DELACK_TIMER_DEFERRED, /* tcp_delack_timer() found socket was owned */
};
static inline struct tcp_sock *tcp_sk(const struct sock *sk)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index bc7c134..e19124b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -350,6 +350,8 @@ extern int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
extern int tcp_sendpage(struct sock *sk, struct page *page, int offset,
size_t size, int flags);
extern void tcp_release_cb(struct sock *sk);
+extern void tcp_write_timer_handler(struct sock *sk);
+extern void tcp_delack_timer_handler(struct sock *sk);
extern int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
extern int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
const struct tcphdr *th, unsigned int len);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 27a32ac..950aebf 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -837,6 +837,13 @@ struct tsq_tasklet {
};
static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
+static void tcp_tsq_handler(struct sock *sk)
+{
+ if ((1 << sk->sk_state) &
+ (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
+ TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
+ tcp_write_xmit(sk, tcp_current_mss(sk), 0, 0, GFP_ATOMIC);
+}
/*
* One tasklest per cpu tries to send more skbs.
* We run in tasklet context but need to disable irqs when
@@ -864,16 +871,10 @@ static void tcp_tasklet_func(unsigned long data)
bh_lock_sock(sk);
if (!sock_owned_by_user(sk)) {
- if ((1 << sk->sk_state) &
- (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 |
- TCPF_CLOSING | TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
- tcp_write_xmit(sk,
- tcp_current_mss(sk),
- 0, 0,
- GFP_ATOMIC);
+ tcp_tsq_handler(sk);
} else {
/* defer the work to tcp_release_cb() */
- set_bit(TSQ_OWNED, &tp->tsq_flags);
+ set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
}
bh_unlock_sock(sk);
@@ -882,6 +883,9 @@ static void tcp_tasklet_func(unsigned long data)
}
}
+#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
+ (1UL << TCP_WRITE_TIMER_DEFERRED) | \
+ (1UL << TCP_DELACK_TIMER_DEFERRED))
/**
* tcp_release_cb - tcp release_sock() callback
* @sk: socket
@@ -892,16 +896,24 @@ static void tcp_tasklet_func(unsigned long data)
void tcp_release_cb(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
+ unsigned long flags, nflags;
- if (test_and_clear_bit(TSQ_OWNED, &tp->tsq_flags)) {
- if ((1 << sk->sk_state) &
- (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 |
- TCPF_CLOSING | TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
- tcp_write_xmit(sk,
- tcp_current_mss(sk),
- 0, 0,
- GFP_ATOMIC);
- }
+ /* perform an atomic operation only if at least one flag is set */
+ do {
+ flags = tp->tsq_flags;
+ if (!(flags & TCP_DEFERRED_ALL))
+ return;
+ nflags = flags & ~TCP_DEFERRED_ALL;
+ } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
+
+ if (flags & (1UL << TCP_TSQ_DEFERRED))
+ tcp_tsq_handler(sk);
+
+ if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED))
+ tcp_write_timer_handler(sk);
+
+ if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED))
+ tcp_delack_timer_handler(sk);
}
EXPORT_SYMBOL(tcp_release_cb);
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index e911e6c..6df36ad 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -32,17 +32,6 @@ int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
int sysctl_tcp_orphan_retries __read_mostly;
int sysctl_tcp_thin_linear_timeouts __read_mostly;
-static void tcp_write_timer(unsigned long);
-static void tcp_delack_timer(unsigned long);
-static void tcp_keepalive_timer (unsigned long data);
-
-void tcp_init_xmit_timers(struct sock *sk)
-{
- inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
- &tcp_keepalive_timer);
-}
-EXPORT_SYMBOL(tcp_init_xmit_timers);
-
static void tcp_write_err(struct sock *sk)
{
sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
@@ -205,21 +194,11 @@ static int tcp_write_timeout(struct sock *sk)
return 0;
}
-static void tcp_delack_timer(unsigned long data)
+void tcp_delack_timer_handler(struct sock *sk)
{
- struct sock *sk = (struct sock *)data;
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
- bh_lock_sock(sk);
- if (sock_owned_by_user(sk)) {
- /* Try again later. */
- icsk->icsk_ack.blocked = 1;
- NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
- sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
- goto out_unlock;
- }
-
sk_mem_reclaim_partial(sk);
if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
@@ -260,7 +239,21 @@ static void tcp_delack_timer(unsigned long data)
out:
if (sk_under_memory_pressure(sk))
sk_mem_reclaim(sk);
-out_unlock:
+}
+
+static void tcp_delack_timer(unsigned long data)
+{
+ struct sock *sk = (struct sock *)data;
+
+ bh_lock_sock(sk);
+ if (!sock_owned_by_user(sk)) {
+ tcp_delack_timer_handler(sk);
+ } else {
+ inet_csk(sk)->icsk_ack.blocked = 1;
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
+ /* deleguate our work to tcp_release_cb() */
+ set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags);
+ }
bh_unlock_sock(sk);
sock_put(sk);
}
@@ -450,19 +443,11 @@ out_reset_timer:
out:;
}
-static void tcp_write_timer(unsigned long data)
+void tcp_write_timer_handler(struct sock *sk)
{
- struct sock *sk = (struct sock *)data;
struct inet_connection_sock *icsk = inet_csk(sk);
int event;
- bh_lock_sock(sk);
- if (sock_owned_by_user(sk)) {
- /* Try again later */
- sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
- goto out_unlock;
- }
-
if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
goto out;
@@ -485,7 +470,19 @@ static void tcp_write_timer(unsigned long data)
out:
sk_mem_reclaim(sk);
-out_unlock:
+}
+
+static void tcp_write_timer(unsigned long data)
+{
+ struct sock *sk = (struct sock *)data;
+
+ bh_lock_sock(sk);
+ if (!sock_owned_by_user(sk)) {
+ tcp_write_timer_handler(sk);
+ } else {
+ /* deleguate our work to tcp_release_cb() */
+ set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags);
+ }
bh_unlock_sock(sk);
sock_put(sk);
}
@@ -602,3 +599,10 @@ out:
bh_unlock_sock(sk);
sock_put(sk);
}
+
+void tcp_init_xmit_timers(struct sock *sk)
+{
+ inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
+ &tcp_keepalive_timer);
+}
+EXPORT_SYMBOL(tcp_init_xmit_timers);
--
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