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authorEric Dumazet <eric.dumazet@gmail.com>2012-07-11 05:50:31 +0000
committerDavid S. Miller <davem@davemloft.net>2012-07-11 18:12:59 -0700
commit46d3ceabd8d98ed0ad10f20c595ca784e34786c5 (patch)
tree771200292431be56c6ebcb23af9206bc03d40e65
parent2100844ca9d7055d5cddce2f8ed13af94c01f85b (diff)
tcp: TCP Small Queues
This introduce TSQ (TCP Small Queues) TSQ goal is to reduce number of TCP packets in xmit queues (qdisc & device queues), to reduce RTT and cwnd bias, part of the bufferbloat problem. sk->sk_wmem_alloc not allowed to grow above a given limit, allowing no more than ~128KB [1] per tcp socket in qdisc/dev layers at a given time. TSO packets are sized/capped to half the limit, so that we have two TSO packets in flight, allowing better bandwidth use. As a side effect, setting the limit to 40000 automatically reduces the standard gso max limit (65536) to 40000/2 : It can help to reduce latencies of high prio packets, having smaller TSO packets. This means we divert sock_wfree() to a tcp_wfree() handler, to queue/send following frames when skb_orphan() [2] is called for the already queued skbs. Results on my dev machines (tg3/ixgbe nics) are really impressive, using standard pfifo_fast, and with or without TSO/GSO. Without reduction of nominal bandwidth, we have reduction of buffering per bulk sender : < 1ms on Gbit (instead of 50ms with TSO) < 8ms on 100Mbit (instead of 132 ms) I no longer have 4 MBytes backlogged in qdisc by a single netperf session, and both side socket autotuning no longer use 4 Mbytes. As skb destructor cannot restart xmit itself ( as qdisc lock might be taken at this point ), we delegate the work to a tasklet. We use one tasklest per cpu for performance reasons. If tasklet finds a socket owned by the user, it sets TSQ_OWNED flag. This flag is tested in a new protocol method called from release_sock(), to eventually send new segments. [1] New /proc/sys/net/ipv4/tcp_limit_output_bytes tunable [2] skb_orphan() is usually called at TX completion time, but some drivers call it in their start_xmit() handler. These drivers should at least use BQL, or else a single TCP session can still fill the whole NIC TX ring, since TSQ will have no effect. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Tom Herbert <therbert@google.com> Cc: Matt Mathis <mattmathis@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Nandita Dukkipati <nanditad@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--Documentation/networking/ip-sysctl.txt14
-rw-r--r--include/linux/tcp.h9
-rw-r--r--include/net/sock.h2
-rw-r--r--include/net/tcp.h4
-rw-r--r--net/core/sock.c4
-rw-r--r--net/ipv4/sysctl_net_ipv4.c7
-rw-r--r--net/ipv4/tcp.c6
-rw-r--r--net/ipv4/tcp_ipv4.c1
-rw-r--r--net/ipv4/tcp_minisocks.c1
-rw-r--r--net/ipv4/tcp_output.c154
-rw-r--r--net/ipv6/tcp_ipv6.c1
11 files changed, 202 insertions, 1 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 47b6c79..e20c17a 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -551,6 +551,20 @@ tcp_thin_dupack - BOOLEAN
Documentation/networking/tcp-thin.txt
Default: 0
+tcp_limit_output_bytes - INTEGER
+ Controls TCP Small Queue limit per tcp socket.
+ TCP bulk sender tends to increase packets in flight until it
+ gets losses notifications. With SNDBUF autotuning, this can
+ result in a large amount of packets queued in qdisc/device
+ on the local machine, hurting latency of other flows, for
+ typical pfifo_fast qdiscs.
+ tcp_limit_output_bytes limits the number of bytes on qdisc
+ or device to reduce artificial RTT/cwnd and reduce bufferbloat.
+ Note: For GSO/TSO enabled flows, we try to have at least two
+ packets in flight. Reducing tcp_limit_output_bytes might also
+ reduce the size of individual GSO packet (64KB being the max)
+ Default: 131072
+
UDP variables:
udp_mem - vector of 3 INTEGERs: min, pressure, max
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 2de9cf4..1888169 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -339,6 +339,9 @@ struct tcp_sock {
u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */
u32 lsndtime; /* timestamp of last sent data packet (for restart window) */
+ struct list_head tsq_node; /* anchor in tsq_tasklet.head list */
+ unsigned long tsq_flags;
+
/* Data for direct copy to user */
struct {
struct sk_buff_head prequeue;
@@ -494,6 +497,12 @@ struct tcp_sock {
struct tcp_cookie_values *cookie_values;
};
+enum tsq_flags {
+ TSQ_THROTTLED,
+ TSQ_QUEUED,
+ TSQ_OWNED, /* tcp_tasklet_func() found socket was locked */
+};
+
static inline struct tcp_sock *tcp_sk(const struct sock *sk)
{
return (struct tcp_sock *)sk;
diff --git a/include/net/sock.h b/include/net/sock.h
index dcb54a0..88de092 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -858,6 +858,8 @@ struct proto {
int (*backlog_rcv) (struct sock *sk,
struct sk_buff *skb);
+ void (*release_cb)(struct sock *sk);
+
/* Keeping track of sk's, looking them up, and port selection methods. */
void (*hash)(struct sock *sk);
void (*unhash)(struct sock *sk);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 3618fef..439984b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -253,6 +253,7 @@ extern int sysctl_tcp_cookie_size;
extern int sysctl_tcp_thin_linear_timeouts;
extern int sysctl_tcp_thin_dupack;
extern int sysctl_tcp_early_retrans;
+extern int sysctl_tcp_limit_output_bytes;
extern atomic_long_t tcp_memory_allocated;
extern struct percpu_counter tcp_sockets_allocated;
@@ -321,6 +322,8 @@ extern struct proto tcp_prot;
extern void tcp_init_mem(struct net *net);
+extern void tcp_tasklet_init(void);
+
extern void tcp_v4_err(struct sk_buff *skb, u32);
extern void tcp_shutdown (struct sock *sk, int how);
@@ -334,6 +337,7 @@ extern int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
size_t size);
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 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/core/sock.c b/net/core/sock.c
index 929bdcc..24039ac 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2159,6 +2159,10 @@ void release_sock(struct sock *sk)
spin_lock_bh(&sk->sk_lock.slock);
if (sk->sk_backlog.tail)
__release_sock(sk);
+
+ if (sk->sk_prot->release_cb)
+ sk->sk_prot->release_cb(sk);
+
sk->sk_lock.owned = 0;
if (waitqueue_active(&sk->sk_lock.wq))
wake_up(&sk->sk_lock.wq);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 12aa0c5..70730f7 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -598,6 +598,13 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
+ {
+ .procname = "tcp_limit_output_bytes",
+ .data = &sysctl_tcp_limit_output_bytes,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
#ifdef CONFIG_NET_DMA
{
.procname = "tcp_dma_copybreak",
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index d902da9..4252cd8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -376,6 +376,7 @@ void tcp_init_sock(struct sock *sk)
skb_queue_head_init(&tp->out_of_order_queue);
tcp_init_xmit_timers(sk);
tcp_prequeue_init(tp);
+ INIT_LIST_HEAD(&tp->tsq_node);
icsk->icsk_rto = TCP_TIMEOUT_INIT;
tp->mdev = TCP_TIMEOUT_INIT;
@@ -796,6 +797,10 @@ static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now,
inet_csk(sk)->icsk_ext_hdr_len -
tp->tcp_header_len);
+ /* TSQ : try to have two TSO segments in flight */
+ xmit_size_goal = min_t(u32, xmit_size_goal,
+ sysctl_tcp_limit_output_bytes >> 1);
+
xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
/* We try hard to avoid divides here */
@@ -3574,4 +3579,5 @@ void __init tcp_init(void)
tcp_secret_primary = &tcp_secret_one;
tcp_secret_retiring = &tcp_secret_two;
tcp_secret_secondary = &tcp_secret_two;
+ tcp_tasklet_init();
}
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ddefd39..01545a3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2588,6 +2588,7 @@ struct proto tcp_prot = {
.sendmsg = tcp_sendmsg,
.sendpage = tcp_sendpage,
.backlog_rcv = tcp_v4_do_rcv,
+ .release_cb = tcp_release_cb,
.hash = inet_hash,
.unhash = inet_unhash,
.get_port = inet_csk_get_port,
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 6560886..c66f2ed 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -424,6 +424,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
treq->snt_isn + 1 + tcp_s_data_size(oldtp);
tcp_prequeue_init(newtp);
+ INIT_LIST_HEAD(&newtp->tsq_node);
tcp_init_wl(newtp, treq->rcv_isn);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c465d3e..03854ab 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -50,6 +50,9 @@ int sysctl_tcp_retrans_collapse __read_mostly = 1;
*/
int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
+/* Default TSQ limit of two TSO segments */
+int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
+
/* This limits the percentage of the congestion window which we
* will allow a single TSO frame to consume. Building TSO frames
* which are too large can cause TCP streams to be bursty.
@@ -65,6 +68,8 @@ int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);
+static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
+ int push_one, gfp_t gfp);
/* Account for new data that has been sent to the network. */
static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
@@ -783,6 +788,140 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
return size;
}
+
+/* TCP SMALL QUEUES (TSQ)
+ *
+ * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
+ * to reduce RTT and bufferbloat.
+ * We do this using a special skb destructor (tcp_wfree).
+ *
+ * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
+ * needs to be reallocated in a driver.
+ * The invariant being skb->truesize substracted from sk->sk_wmem_alloc
+ *
+ * Since transmit from skb destructor is forbidden, we use a tasklet
+ * to process all sockets that eventually need to send more skbs.
+ * We use one tasklet per cpu, with its own queue of sockets.
+ */
+struct tsq_tasklet {
+ struct tasklet_struct tasklet;
+ struct list_head head; /* queue of tcp sockets */
+};
+static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
+
+/*
+ * One tasklest per cpu tries to send more skbs.
+ * We run in tasklet context but need to disable irqs when
+ * transfering tsq->head because tcp_wfree() might
+ * interrupt us (non NAPI drivers)
+ */
+static void tcp_tasklet_func(unsigned long data)
+{
+ struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
+ LIST_HEAD(list);
+ unsigned long flags;
+ struct list_head *q, *n;
+ struct tcp_sock *tp;
+ struct sock *sk;
+
+ local_irq_save(flags);
+ list_splice_init(&tsq->head, &list);
+ local_irq_restore(flags);
+
+ list_for_each_safe(q, n, &list) {
+ tp = list_entry(q, struct tcp_sock, tsq_node);
+ list_del(&tp->tsq_node);
+
+ sk = (struct sock *)tp;
+ 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))
+ tcp_write_xmit(sk,
+ tcp_current_mss(sk),
+ 0, 0,
+ GFP_ATOMIC);
+ } else {
+ /* defer the work to tcp_release_cb() */
+ set_bit(TSQ_OWNED, &tp->tsq_flags);
+ }
+ bh_unlock_sock(sk);
+
+ clear_bit(TSQ_QUEUED, &tp->tsq_flags);
+ sk_free(sk);
+ }
+}
+
+/**
+ * tcp_release_cb - tcp release_sock() callback
+ * @sk: socket
+ *
+ * called from release_sock() to perform protocol dependent
+ * actions before socket release.
+ */
+void tcp_release_cb(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ 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))
+ tcp_write_xmit(sk,
+ tcp_current_mss(sk),
+ 0, 0,
+ GFP_ATOMIC);
+ }
+}
+EXPORT_SYMBOL(tcp_release_cb);
+
+void __init tcp_tasklet_init(void)
+{
+ int i;
+
+ for_each_possible_cpu(i) {
+ struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
+
+ INIT_LIST_HEAD(&tsq->head);
+ tasklet_init(&tsq->tasklet,
+ tcp_tasklet_func,
+ (unsigned long)tsq);
+ }
+}
+
+/*
+ * Write buffer destructor automatically called from kfree_skb.
+ * We cant xmit new skbs from this context, as we might already
+ * hold qdisc lock.
+ */
+void tcp_wfree(struct sk_buff *skb)
+{
+ struct sock *sk = skb->sk;
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
+ !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
+ unsigned long flags;
+ struct tsq_tasklet *tsq;
+
+ /* Keep a ref on socket.
+ * This last ref will be released in tcp_tasklet_func()
+ */
+ atomic_sub(skb->truesize - 1, &sk->sk_wmem_alloc);
+
+ /* queue this socket to tasklet queue */
+ local_irq_save(flags);
+ tsq = &__get_cpu_var(tsq_tasklet);
+ list_add(&tp->tsq_node, &tsq->head);
+ tasklet_schedule(&tsq->tasklet);
+ local_irq_restore(flags);
+ } else {
+ sock_wfree(skb);
+ }
+}
+
/* This routine actually transmits TCP packets queued in by
* tcp_do_sendmsg(). This is used by both the initial
* transmission and possible later retransmissions.
@@ -844,7 +983,12 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
skb_push(skb, tcp_header_size);
skb_reset_transport_header(skb);
- skb_set_owner_w(skb, sk);
+
+ skb_orphan(skb);
+ skb->sk = sk;
+ skb->destructor = (sysctl_tcp_limit_output_bytes > 0) ?
+ tcp_wfree : sock_wfree;
+ atomic_add(skb->truesize, &sk->sk_wmem_alloc);
/* Build TCP header and checksum it. */
th = tcp_hdr(skb);
@@ -1780,6 +1924,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
while ((skb = tcp_send_head(sk))) {
unsigned int limit;
+
tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
BUG_ON(!tso_segs);
@@ -1800,6 +1945,13 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
break;
}
+ /* TSQ : sk_wmem_alloc accounts skb truesize,
+ * including skb overhead. But thats OK.
+ */
+ if (atomic_read(&sk->sk_wmem_alloc) >= sysctl_tcp_limit_output_bytes) {
+ set_bit(TSQ_THROTTLED, &tp->tsq_flags);
+ break;
+ }
limit = mss_now;
if (tso_segs > 1 && !tcp_urg_mode(tp))
limit = tcp_mss_split_point(sk, skb, mss_now,
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 61175cb..70458a9 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1970,6 +1970,7 @@ struct proto tcpv6_prot = {
.sendmsg = tcp_sendmsg,
.sendpage = tcp_sendpage,
.backlog_rcv = tcp_v6_do_rcv,
+ .release_cb = tcp_release_cb,
.hash = tcp_v6_hash,
.unhash = inet_unhash,
.get_port = inet_csk_get_port,