leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

tcp: move cwnd reduction after recovery state procesing

Browse Source 
Currently the cwnd is reduced and increased in various different
places. The reduction happens in various places in the recovery
state processing (tcp_fastretrans_alert) while the increase
happens afterward.

A better sequence is to identify lost packets and update
the congestion control state (icsk_ca_state) first. Then base
on the new state, up/down the cwnd in one central place. It's
more clear to reason cwnd changes.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2016-02-02 10:33:05 -08:00 committed by David S. Miller
parent e662ca40de
commit 31ba0c1072
1 changed files with 28 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
net/ipv4/tcp_input.c
View File

@ -2471,14 +2471,12 @@ static void tcp_init_cwnd_reduction(struct sock *sk)
tcp_ecn_queue_cwr(tp);
}
static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
int fast_rexmit, int flag)
static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
int sndcnt = 0;
int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
int newly_acked_sacked = prior_unsacked -
(tp->packets_out - tp->sacked_out);
if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
return;
@ -2496,7 +2494,8 @@ static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
} else {
sndcnt = min(delta, newly_acked_sacked);
}
sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
/* Force a fast retransmit upon entering fast recovery */
sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
}
@ -2541,7 +2540,7 @@ static void tcp_try_keep_open(struct sock *sk)
}
}
static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
static void tcp_try_to_open(struct sock *sk, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
@ -2555,8 +2554,6 @@ static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
tcp_try_keep_open(sk);
} else {
tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
}
}
@ -2720,8 +2717,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
}
/* Undo during fast recovery after partial ACK. */
static bool tcp_try_undo_partial(struct sock *sk, const int acked,
const int prior_unsacked, int flag)
static bool tcp_try_undo_partial(struct sock *sk, const int acked)
{
struct tcp_sock *tp = tcp_sk(sk);
@ -2736,10 +2732,8 @@ static bool tcp_try_undo_partial(struct sock *sk, const int acked,
* can undo. Otherwise we clock out new packets but do not
* mark more packets lost or retransmit more.
*/
if (tp->retrans_out) {
tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
if (tp->retrans_out)
return true;
}
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
@ -2758,21 +2752,21 @@ static bool tcp_try_undo_partial(struct sock *sk, const int acked,
* taking into account both packets sitting in receiver's buffer and
* packets lost by network.
*
* Besides that it does CWND reduction, when packet loss is detected
* and changes state of machine.
* Besides that it updates the congestion state when packet loss or ECN
* is detected. But it does not reduce the cwnd, it is done by the
* congestion control later.
*
* It does _not_ decide what to send, it is made in function
* tcp_xmit_retransmit_queue().
*/
static void tcp_fastretrans_alert(struct sock *sk, const int acked,
const int prior_unsacked,
bool is_dupack, int flag, int *rexmit)
bool is_dupack, int *ack_flag, int *rexmit)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int fast_rexmit = 0, flag = *ack_flag;
bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
(tcp_fackets_out(tp) > tp->reordering));
int fast_rexmit = 0;
if (WARN_ON(!tp->packets_out && tp->sacked_out))
tp->sacked_out = 0;
@ -2819,8 +2813,10 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
/* Use RACK to detect loss */
if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS &&
tcp_rack_mark_lost(sk))
tcp_rack_mark_lost(sk)) {
flag |= FLAG_LOST_RETRANS;
*ack_flag |= FLAG_LOST_RETRANS;
}
/* E. Process state. */
switch (icsk->icsk_ca_state) {
@ -2829,7 +2825,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
if (tcp_is_reno(tp) && is_dupack)
tcp_add_reno_sack(sk);
} else {
if (tcp_try_undo_partial(sk, acked, prior_unsacked, flag))
if (tcp_try_undo_partial(sk, acked))
return;
/* Partial ACK arrived. Force fast retransmit. */
do_lost = tcp_is_reno(tp) ||
@ -2858,7 +2854,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
tcp_try_undo_dsack(sk);
if (!tcp_time_to_recover(sk, flag)) {
tcp_try_to_open(sk, flag, prior_unsacked);
tcp_try_to_open(sk, flag);
return;
}
@ -2880,7 +2876,6 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
if (do_lost)
tcp_update_scoreboard(sk, fast_rexmit);
tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
*rexmit = REXMIT_LOST;
}
@ -3306,9 +3301,6 @@ static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
/* Decide wheather to run the increase function of congestion control. */
static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
{
if (tcp_in_cwnd_reduction(sk))
return false;
/* If reordering is high then always grow cwnd whenever data is
* delivered regardless of its ordering. Otherwise stay conservative
* and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
@ -3551,6 +3543,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
int prior_packets = tp->packets_out;
const int prior_unsacked = tp->packets_out - tp->sacked_out;
int acked = 0; /* Number of packets newly acked */
int acked_sacked; /* Number of packets newly acked or sacked */
int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
sack_state.first_sackt.v64 = 0;
@ -3647,15 +3640,20 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
if (tcp_ack_is_dubious(sk, flag)) {
is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
tcp_fastretrans_alert(sk, acked, prior_unsacked,
is_dupack, flag, &rexmit);
tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
}
if (tp->tlp_high_seq)
tcp_process_tlp_ack(sk, ack, flag);
acked_sacked = prior_unsacked - (tp->packets_out - tp->sacked_out);
/* Advance cwnd if state allows */
if (tcp_may_raise_cwnd(sk, flag))
if (tcp_in_cwnd_reduction(sk)) {
/* Reduce cwnd if state mandates */
tcp_cwnd_reduction(sk, acked_sacked, flag);
} else if (tcp_may_raise_cwnd(sk, flag)) {
/* Advance cwnd if state allows */
tcp_cong_avoid(sk, ack, acked);
}
if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
struct dst_entry *dst = __sk_dst_get(sk);
@ -3672,8 +3670,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
no_queue:
/* If data was DSACKed, see if we can undo a cwnd reduction. */
if (flag & FLAG_DSACKING_ACK)
tcp_fastretrans_alert(sk, acked, prior_unsacked,
is_dupack, flag, &rexmit);
tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
/* If this ack opens up a zero window, clear backoff. It was
* being used to time the probes, and is probably far higher than
* it needs to be for normal retransmission.
@ -3696,8 +3693,7 @@ old_ack:
if (TCP_SKB_CB(skb)->sacked) {
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
&sack_state);
tcp_fastretrans_alert(sk, acked, prior_unsacked,
is_dupack, flag, &rexmit);
tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
tcp_xmit_recovery(sk, rexmit);
}