Commit 2b195850 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: add tp->dup_ack_counter 



In commit 86de5921 ("tcp: defer SACK compression after DupThresh")
I added a TCP_FASTRETRANS_THRESH bias to tp->compressed_ack in order
to enable sack compression only after 3 dupacks.

Since we plan to relax this rule for flows that involve
stacks not requiring this old rule, this patch adds
a distinct tp->dup_ack_counter.

This means the TCP_FASTRETRANS_THRESH value is now used
in a single location that a future patch can adjust:

	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
		tp->dup_ack_counter++;
		goto send_now;
	}

This patch also introduces tcp_sack_compress_send_ack()
helper to ease following patch comprehension.

This patch refines LINUX_MIB_TCPACKCOMPRESSED to not
count the acks that we had to send if the timer expires
or tcp_sack_compress_send_ack() is sending an ack.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-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 3857c776

include/linux/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -268,6 +268,7 @@ struct tcp_sock { 
	} rack;

	u16	advmss;		/* Advertised MSS			*/

	u8	compressed_ack;

	u8	dup_ack_counter;

	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 */

net/ipv4/tcp_input.c

+27 −9
Original line number Diff line number Diff line
@@ -4327,6 +4327,27 @@ static void tcp_sack_maybe_coalesce(struct tcp_sock *tp) 
	}

}



static void tcp_sack_compress_send_ack(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);



	if (!tp->compressed_ack)

		return;



	if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)

		__sock_put(sk);



	/* Since we have to send one ack finally,

	 * substract one from tp->compressed_ack to keep

	 * LINUX_MIB_TCPACKCOMPRESSED accurate.

	 */

	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,

		      tp->compressed_ack - 1);



	tp->compressed_ack = 0;

	tcp_send_ack(sk);

}



static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)

{

	struct tcp_sock *tp = tcp_sk(sk);
@@ -4355,8 +4376,7 @@ static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 
	 * If the sack array is full, forget about the last one.

	 */

	if (this_sack >= TCP_NUM_SACKS) {

		if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)

			tcp_send_ack(sk);

		tcp_sack_compress_send_ack(sk);

		this_sack--;

		tp->rx_opt.num_sacks--;

		sp--;
@@ -5275,15 +5295,13 @@ send_now: 


	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {

		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;

		if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)

			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,

				      tp->compressed_ack - TCP_FASTRETRANS_THRESH);

		tp->compressed_ack = 0;

		tp->dup_ack_counter = 0;

	}



	if (++tp->compressed_ack <= TCP_FASTRETRANS_THRESH)

	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {

		tp->dup_ack_counter++;

		goto send_now;



	}

	tp->compressed_ack++;

	if (hrtimer_is_queued(&tp->compressed_ack_timer))

		return;

net/ipv4/tcp_output.c

+3 −3
Original line number Diff line number Diff line
@@ -184,10 +184,10 @@ static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts, 
{

	struct tcp_sock *tp = tcp_sk(sk);



	if (unlikely(tp->compressed_ack > TCP_FASTRETRANS_THRESH)) {

	if (unlikely(tp->compressed_ack)) {

		NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,

			      tp->compressed_ack - TCP_FASTRETRANS_THRESH);

		tp->compressed_ack = TCP_FASTRETRANS_THRESH;

			      tp->compressed_ack);

		tp->compressed_ack = 0;

		if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)

			__sock_put(sk);

	}

net/ipv4/tcp_timer.c

+7 −1
Original line number Diff line number Diff line
@@ -753,8 +753,14 @@ static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer) 


	bh_lock_sock(sk);

	if (!sock_owned_by_user(sk)) {

		if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)

		if (tp->compressed_ack) {

			/* Since we have to send one ack finally,

			 * substract one from tp->compressed_ack to keep

			 * LINUX_MIB_TCPACKCOMPRESSED accurate.

			 */

			tp->compressed_ack--;

			tcp_send_ack(sk);

		}

	} else {

		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,

				      &sk->sk_tsq_flags))

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