Re: [PATCH v2] tcp: avoid cwnd moderation in undo
From: David Miller <davem@davemloft.net>
Date: 2011-03-23 02:37:02
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
From: Yuchung Cheng <redacted> Date: Mon, 14 Mar 2011 13:57:03 -0700
In the current undo logic, cwnd is moderated after it was restored to the value prior entering fast-recovery. It was moderated first in tcp_try_undo_recovery then again in tcp_complete_cwr. Since the undo indicates recovery was false, these moderations are not necessary. If the undo is triggered when most of the outstanding data have been acknowledged, the (restored) cwnd is falsely pulled down to a small value. This patch removes these cwnd moderations if cwnd is undone a) during fast-recovery b) by receiving DSACKs past fast-recovery Signed-off-by: Yuchung Cheng <redacted>
Applied, thank you. I followed it up with this tidy up: -------------------- tcp: Make undo_ssthresh arg to tcp_undo_cwr() a bool. Signed-off-by: David S. Miller <davem@davemloft.net> --- net/ipv4/tcp_input.c | 12 ++++++------ 1 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e72af7e..bef9f04 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c@@ -2659,7 +2659,7 @@ static void DBGUNDO(struct sock *sk, const char *msg) #define DBGUNDO(x...) do { } while (0) #endif -static void tcp_undo_cwr(struct sock *sk, const int undo_ssthresh) +static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh) { struct tcp_sock *tp = tcp_sk(sk);
@@ -2698,7 +2698,7 @@ static int tcp_try_undo_recovery(struct sock *sk) * or our original transmission succeeded. */ DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); - tcp_undo_cwr(sk, 1); + tcp_undo_cwr(sk, true); if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) mib_idx = LINUX_MIB_TCPLOSSUNDO; else
@@ -2725,7 +2725,7 @@ static void tcp_try_undo_dsack(struct sock *sk) if (tp->undo_marker && !tp->undo_retrans) { DBGUNDO(sk, "D-SACK"); - tcp_undo_cwr(sk, 1); + tcp_undo_cwr(sk, true); tp->undo_marker = 0; NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); }
@@ -2778,7 +2778,7 @@ static int tcp_try_undo_partial(struct sock *sk, int acked) tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1); DBGUNDO(sk, "Hoe"); - tcp_undo_cwr(sk, 0); + tcp_undo_cwr(sk, false); NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); /* So... Do not make Hoe's retransmit yet.
@@ -2807,7 +2807,7 @@ static int tcp_try_undo_loss(struct sock *sk) DBGUNDO(sk, "partial loss"); tp->lost_out = 0; - tcp_undo_cwr(sk, 1); + tcp_undo_cwr(sk, true); NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO); inet_csk(sk)->icsk_retransmits = 0; tp->undo_marker = 0;
@@ -3496,7 +3496,7 @@ static void tcp_undo_spur_to_response(struct sock *sk, int flag) if (flag & FLAG_ECE) tcp_ratehalving_spur_to_response(sk); else - tcp_undo_cwr(sk, 1); + tcp_undo_cwr(sk, true); } /* F-RTO spurious RTO detection algorithm (RFC4138)
--
1.7.4.1