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tcp: add tp->dup_ack_counter

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In commit 86de5921a3 ("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: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2020-04-30 10:35:41 -07:00 committed by David S. Miller
parent 3857c77624
commit 2b19585012
4 changed files with 38 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/tcp.h
View File

@ -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 */

36
net/ipv4/tcp_input.c
View File

@ -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;

6
net/ipv4/tcp_output.c
View File

@ -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);
}

8
net/ipv4/tcp_timer.c
View File

@ -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))