Commit a11238ec authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'dctcp' 



Daniel Borkmann says:

====================
net: tcp: DCTCP congestion control algorithm

This patch series adds support for the DataCenter TCP (DCTCP) congestion
control algorithm. Please see individual patches for the details.

The last patch adds DCTCP as a congestion control module, and previous
ones add needed infrastructure to extend the congestion control framework.

Joint work between Florian Westphal, Daniel Borkmann and Glenn Judd.

v3 -> v2:
 - No changes anywhere, just a resend as requested by Dave
 - Added Stephen's ACK
v1 -> v2:
 - Rebased to latest net-next
 - Addressed Eric's feedback, thanks!
  - Update stale comment wrt. DCTCP ECN usage
  - Don't call INET_ECN_xmit for every packet
 - Add dctcp ss/inetdiag support to expose internal stats to userspace
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 53dfd501 e3118e83

Documentation/networking/dctcp.txt

0 → 100644
+43 −0
Original line number Diff line number Diff line 
DCTCP (DataCenter TCP)

----------------------



DCTCP is an enhancement to the TCP congestion control algorithm for data

center networks and leverages Explicit Congestion Notification (ECN) in

the data center network to provide multi-bit feedback to the end hosts.



To enable it on end hosts:



  sysctl -w net.ipv4.tcp_congestion_control=dctcp



All switches in the data center network running DCTCP must support ECN

marking and be configured for marking when reaching defined switch buffer

thresholds. The default ECN marking threshold heuristic for DCTCP on

switches is 20 packets (30KB) at 1Gbps, and 65 packets (~100KB) at 10Gbps,

but might need further careful tweaking.



For more details, see below documents:



Paper:



The algorithm is further described in detail in the following two

SIGCOMM/SIGMETRICS papers:



 i) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye,

    Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan:

      "Data Center TCP (DCTCP)", Data Center Networks session

      Proc. ACM SIGCOMM, New Delhi, 2010.

    http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf

    http://www.sigcomm.org/ccr/papers/2010/October/1851275.1851192



ii) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar:

      "Analysis of DCTCP: Stability, Convergence, and Fairness"

      Proc. ACM SIGMETRICS, San Jose, 2011.

    http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf



IETF informational draft:



  http://tools.ietf.org/html/draft-bensley-tcpm-dctcp-00



DCTCP site:



  http://simula.stanford.edu/~alizade/Site/DCTCP.html

include/net/tcp.h

+58 −20
Original line number Diff line number Diff line
@@ -733,23 +733,6 @@ struct tcp_skb_cb { 


#define TCP_SKB_CB(__skb)	((struct tcp_skb_cb *)&((__skb)->cb[0]))



/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set

 *

 * If we receive a SYN packet with these bits set, it means a network is

 * playing bad games with TOS bits. In order to avoid possible false congestion

 * notifications, we disable TCP ECN negociation.

 */

static inline void

TCP_ECN_create_request(struct request_sock *req, const struct sk_buff *skb,

		struct net *net)

{

	const struct tcphdr *th = tcp_hdr(skb);



	if (net->ipv4.sysctl_tcp_ecn && th->ece && th->cwr &&

	    INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield))

		inet_rsk(req)->ecn_ok = 1;

}



/* Due to TSO, an SKB can be composed of multiple actual

 * packets.  To keep these tracked properly, we use this.

 */
@@ -780,8 +763,17 @@ enum tcp_ca_event { 
	CA_EVENT_CWND_RESTART,	/* congestion window restart */

	CA_EVENT_COMPLETE_CWR,	/* end of congestion recovery */

	CA_EVENT_LOSS,		/* loss timeout */

	CA_EVENT_FAST_ACK,	/* in sequence ack */

	CA_EVENT_SLOW_ACK,	/* other ack */

	CA_EVENT_ECN_NO_CE,	/* ECT set, but not CE marked */

	CA_EVENT_ECN_IS_CE,	/* received CE marked IP packet */

	CA_EVENT_DELAYED_ACK,	/* Delayed ack is sent */

	CA_EVENT_NON_DELAYED_ACK,

};



/* Information about inbound ACK, passed to cong_ops->in_ack_event() */

enum tcp_ca_ack_event_flags {

	CA_ACK_SLOWPATH		= (1 << 0),	/* In slow path processing */

	CA_ACK_WIN_UPDATE	= (1 << 1),	/* ACK updated window */

	CA_ACK_ECE		= (1 << 2),	/* ECE bit is set on ack */

};



/*
@@ -791,7 +783,10 @@ enum tcp_ca_event { 
#define TCP_CA_MAX	128

#define TCP_CA_BUF_MAX	(TCP_CA_NAME_MAX*TCP_CA_MAX)



/* Algorithm can be set on socket without CAP_NET_ADMIN privileges */

#define TCP_CONG_NON_RESTRICTED 0x1

/* Requires ECN/ECT set on all packets */

#define TCP_CONG_NEEDS_ECN	0x2



struct tcp_congestion_ops {

	struct list_head	list;
@@ -810,6 +805,8 @@ struct tcp_congestion_ops { 
	void (*set_state)(struct sock *sk, u8 new_state);

	/* call when cwnd event occurs (optional) */

	void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);

	/* call when ack arrives (optional) */

	void (*in_ack_event)(struct sock *sk, u32 flags);

	/* new value of cwnd after loss (optional) */

	u32  (*undo_cwnd)(struct sock *sk);

	/* hook for packet ack accounting (optional) */
@@ -824,6 +821,7 @@ struct tcp_congestion_ops { 
int tcp_register_congestion_control(struct tcp_congestion_ops *type);

void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);



void tcp_assign_congestion_control(struct sock *sk);

void tcp_init_congestion_control(struct sock *sk);

void tcp_cleanup_congestion_control(struct sock *sk);

int tcp_set_default_congestion_control(const char *name);
@@ -835,11 +833,17 @@ int tcp_set_congestion_control(struct sock *sk, const char *name); 
int tcp_slow_start(struct tcp_sock *tp, u32 acked);

void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w);



extern struct tcp_congestion_ops tcp_init_congestion_ops;

u32 tcp_reno_ssthresh(struct sock *sk);

void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);

extern struct tcp_congestion_ops tcp_reno;



static inline bool tcp_ca_needs_ecn(const struct sock *sk)

{

	const struct inet_connection_sock *icsk = inet_csk(sk);



	return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;

}



static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)

{

	struct inet_connection_sock *icsk = inet_csk(sk);
@@ -857,6 +861,40 @@ static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event) 
		icsk->icsk_ca_ops->cwnd_event(sk, event);

}



/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set

 *

 * If we receive a SYN packet with these bits set, it means a

 * network is playing bad games with TOS bits. In order to

 * avoid possible false congestion notifications, we disable

 * TCP ECN negociation.

 *

 * Exception: tcp_ca wants ECN. This is required for DCTCP

 * congestion control; it requires setting ECT on all packets,

 * including SYN. We inverse the test in this case: If our

 * local socket wants ECN, but peer only set ece/cwr (but not

 * ECT in IP header) its probably a non-DCTCP aware sender.

 */

static inline void

TCP_ECN_create_request(struct request_sock *req, const struct sk_buff *skb,

		       const struct sock *listen_sk)

{

	const struct tcphdr *th = tcp_hdr(skb);

	const struct net *net = sock_net(listen_sk);

	bool th_ecn = th->ece && th->cwr;

	bool ect, need_ecn;



	if (!th_ecn)

		return;



	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);

	need_ecn = tcp_ca_needs_ecn(listen_sk);



	if (!ect && !need_ecn && net->ipv4.sysctl_tcp_ecn)

		inet_rsk(req)->ecn_ok = 1;

	else if (ect && need_ecn)

		inet_rsk(req)->ecn_ok = 1;

}



/* These functions determine how the current flow behaves in respect of SACK

 * handling. SACK is negotiated with the peer, and therefore it can vary

 * between different flows.

include/uapi/linux/inet_diag.h

+11 −2
Original line number Diff line number Diff line
@@ -110,10 +110,10 @@ enum { 
	INET_DIAG_TCLASS,

	INET_DIAG_SKMEMINFO,

	INET_DIAG_SHUTDOWN,

	INET_DIAG_DCTCPINFO,

};



#define INET_DIAG_MAX INET_DIAG_SHUTDOWN



#define INET_DIAG_MAX INET_DIAG_DCTCPINFO



/* INET_DIAG_MEM */
@@ -133,5 +133,14 @@ struct tcpvegas_info { 
	__u32	tcpv_minrtt;

};



/* INET_DIAG_DCTCPINFO */



struct tcp_dctcp_info {

	__u16	dctcp_enabled;

	__u16	dctcp_ce_state;

	__u32	dctcp_alpha;

	__u32	dctcp_ab_ecn;

	__u32	dctcp_ab_tot;

};



#endif /* _UAPI_INET_DIAG_H_ */

net/ipv4/Kconfig

+25 −1
Original line number Diff line number Diff line
@@ -570,6 +570,27 @@ config TCP_CONG_ILLINOIS 
	For further details see:

	  http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html



config TCP_CONG_DCTCP

	tristate "DataCenter TCP (DCTCP)"

	default n

	---help---

	DCTCP leverages Explicit Congestion Notification (ECN) in the network to

	provide multi-bit feedback to the end hosts. It is designed to provide:



	- High burst tolerance (incast due to partition/aggregate),

	- Low latency (short flows, queries),

	- High throughput (continuous data updates, large file transfers) with

	  commodity, shallow-buffered switches.



	All switches in the data center network running DCTCP must support

	ECN marking and be configured for marking when reaching defined switch

	buffer thresholds. The default ECN marking threshold heuristic for

	DCTCP on switches is 20 packets (30KB) at 1Gbps, and 65 packets

	(~100KB) at 10Gbps, but might need further careful tweaking.



	For further details see:

	  http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf



choice

	prompt "Default TCP congestion control"

	default DEFAULT_CUBIC
@@ -598,9 +619,11 @@ choice 
	config DEFAULT_WESTWOOD

		bool "Westwood" if TCP_CONG_WESTWOOD=y



	config DEFAULT_DCTCP

		bool "DCTCP" if TCP_CONG_DCTCP=y



	config DEFAULT_RENO

		bool "Reno"



endchoice



endif
@@ -620,6 +643,7 @@ config DEFAULT_TCP_CONG 
	default "westwood" if DEFAULT_WESTWOOD

	default "veno" if DEFAULT_VENO

	default "reno" if DEFAULT_RENO

	default "dctcp" if DEFAULT_DCTCP

	default "cubic"



config TCP_MD5SIG

net/ipv4/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o 
obj-$(CONFIG_NET_TCPPROBE) += tcp_probe.o

obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o

obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o

obj-$(CONFIG_TCP_CONG_DCTCP) += tcp_dctcp.o

obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o

obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o

obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o

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