Commit 05b055e8 authored by Francis Yan's avatar Francis Yan Committed by David S. Miller
Browse files

tcp: instrument tcp sender limits chronographs 



This patch implements the skeleton of the TCP chronograph
instrumentation on sender side limits:

	1) idle (unspec)
	2) busy sending data other than 3-4 below
	3) rwnd-limited
	4) sndbuf-limited

The limits are enumerated 'tcp_chrono'. Since a connection in
theory can idle forever, we do not track the actual length of this
uninteresting idle period. For the rest we track how long the sender
spends in each limit. At any point during the life time of a
connection, the sender must be in one of the four states.

If there are multiple conditions worthy of tracking in a chronograph
then the highest priority enum takes precedence over
the other conditions. So that if something "more interesting"
starts happening, stop the previous chrono and start a new one.

The time unit is jiffy(u32) in order to save space in tcp_sock.
This implies application must sample the stats no longer than every
49 days of 1ms jiffy.

Signed-off-by: default avatarFrancis Yan <francisyyan@gmail.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a0909949

include/linux/tcp.h

+5 −2
Original line number Diff line number Diff line
@@ -211,8 +211,11 @@ struct tcp_sock { 
		u8 reord;    /* reordering detected */

	} rack;

	u16	advmss;		/* Advertised MSS			*/

	u8	rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */

		unused:7;

	u32	chrono_start;	/* Start time in jiffies of a TCP chrono */

	u32	chrono_stat[3];	/* Time in jiffies for chrono_stat stats */

	u8	chrono_type:2,	/* current chronograph type */

		rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */

		unused:5;

	u8	nonagle     : 4,/* Disable Nagle algorithm?             */

		thin_lto    : 1,/* Use linear timeouts for thin streams */

		thin_dupack : 1,/* Fast retransmit on first dupack      */

include/net/tcp.h

+14 −0
Original line number Diff line number Diff line
@@ -1516,6 +1516,20 @@ struct tcp_fastopen_context { 
	struct rcu_head		rcu;

};



/* Latencies incurred by various limits for a sender. They are

 * chronograph-like stats that are mutually exclusive.

 */

enum tcp_chrono {

	TCP_CHRONO_UNSPEC,

	TCP_CHRONO_BUSY, /* Actively sending data (non-empty write queue) */

	TCP_CHRONO_RWND_LIMITED, /* Stalled by insufficient receive window */

	TCP_CHRONO_SNDBUF_LIMITED, /* Stalled by insufficient send buffer */

	__TCP_CHRONO_MAX,

};



void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type);

void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type);



/* write queue abstraction */

static inline void tcp_write_queue_purge(struct sock *sk)

{

net/ipv4/tcp_output.c

+30 −0
Original line number Diff line number Diff line
@@ -2081,6 +2081,36 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb, 
	return false;

}



static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)

{

	const u32 now = tcp_time_stamp;



	if (tp->chrono_type > TCP_CHRONO_UNSPEC)

		tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;

	tp->chrono_start = now;

	tp->chrono_type = new;

}



void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)

{

	struct tcp_sock *tp = tcp_sk(sk);



	/* If there are multiple conditions worthy of tracking in a

	 * chronograph then the highest priority enum takes precedence over

	 * the other conditions. So that if something "more interesting"

	 * starts happening, stop the previous chrono and start a new one.

	 */

	if (type > tp->chrono_type)

		tcp_chrono_set(tp, type);

}



void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)

{

	struct tcp_sock *tp = tcp_sk(sk);



	tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);

}



/* This routine writes packets to the network.  It advances the

 * send_head.  This happens as incoming acks open up the remote

 * window for us.

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