* [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP
@ 2021-07-27 14:42 Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 1/2] tcp: more accurately detect spurious TLP probes Neal Cardwell
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Neal Cardwell @ 2021-07-27 14:42 UTC (permalink / raw)
To: David Miller; +Cc: netdev, Eric Dumazet, Neal Cardwell
This patch series includes two minor improvements to tighten up the accuracy of
the processing of incoming DSACK information, so that RACK-TLP behavior is
faster and more precise: first, to ensure we detect packet loss in some extra
corner cases; and second, to avoid growing the RACK reordering window (and
delaying fast recovery) in cases where it seems clear we don't need to.
Neal Cardwell (1):
tcp: more accurately check DSACKs to grow RACK reordering window
Yuchung Cheng (1):
tcp: more accurately detect spurious TLP probes
net/ipv4/tcp_input.c | 14 ++++++++++++--
net/ipv4/tcp_recovery.c | 3 ++-
2 files changed, 14 insertions(+), 3 deletions(-)
--
2.32.0.432.gabb21c7263-goog
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH net-next 1/2] tcp: more accurately detect spurious TLP probes
2021-07-27 14:42 [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP Neal Cardwell
@ 2021-07-27 14:42 ` Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 2/2] tcp: more accurately check DSACKs to grow RACK reordering window Neal Cardwell
2021-07-27 19:20 ` [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP patchwork-bot+netdevbpf
2 siblings, 0 replies; 4+ messages in thread
From: Neal Cardwell @ 2021-07-27 14:42 UTC (permalink / raw)
To: David Miller
Cc: netdev, Eric Dumazet, Yuchung Cheng, Neal Cardwell, Priyaranjan Jha
From: Yuchung Cheng <ycheng@google.com>
Previously TLP is considered spurious if the sender receives any
DSACK during a TLP episode. This patch further checks the DSACK
sequences match the TLP's to improve accuracy.
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Priyaranjan Jha <priyarjha@google.com>
---
net/ipv4/tcp_input.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 501d8d4d4ba4..98408d520c32 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -100,6 +100,7 @@ int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
#define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */
+#define FLAG_DSACK_TLP 0x20000 /* DSACK for tail loss probe */
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
@@ -991,6 +992,8 @@ static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
return 0;
if (seq_len > tp->mss_cache)
dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
+ else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
+ state->flag |= FLAG_DSACK_TLP;
tp->dsack_dups += dup_segs;
/* Skip the DSACK if dup segs weren't retransmitted by sender */
@@ -3650,7 +3653,7 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
if (!tp->tlp_retrans) {
/* TLP of new data has been acknowledged */
tp->tlp_high_seq = 0;
- } else if (flag & FLAG_DSACKING_ACK) {
+ } else if (flag & FLAG_DSACK_TLP) {
/* This DSACK means original and TLP probe arrived; no loss */
tp->tlp_high_seq = 0;
} else if (after(ack, tp->tlp_high_seq)) {
--
2.32.0.432.gabb21c7263-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH net-next 2/2] tcp: more accurately check DSACKs to grow RACK reordering window
2021-07-27 14:42 [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 1/2] tcp: more accurately detect spurious TLP probes Neal Cardwell
@ 2021-07-27 14:42 ` Neal Cardwell
2021-07-27 19:20 ` [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP patchwork-bot+netdevbpf
2 siblings, 0 replies; 4+ messages in thread
From: Neal Cardwell @ 2021-07-27 14:42 UTC (permalink / raw)
To: David Miller
Cc: netdev, Eric Dumazet, Neal Cardwell, Yuchung Cheng, Priyaranjan Jha
Previously, a DSACK could expand the RACK reordering window when no
reordering has been seen, and/or when the DSACK was due to an
unnecessary TLP retransmit (rather than a spurious fast recovery due
to reordering). This could result in unnecessarily growing the RACK
reordering window and thus unnecessarily delaying RACK-based fast
recovery episodes.
To avoid these issues, this commit tightens the conditions under which
a DSACK triggers the RACK reordering window to grow, so that a
connection only expands its RACK reordering window if:
(a) reordering has been seen in the connection
(b) a DSACKed range does not match the most recent TLP retransmit
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Priyaranjan Jha <priyarjha@google.com>
---
net/ipv4/tcp_input.c | 9 ++++++++-
net/ipv4/tcp_recovery.c | 3 ++-
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 98408d520c32..3f7bd7ae7d7a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1001,7 +1001,14 @@ static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
return 0;
tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
- tp->rack.dsack_seen = 1;
+ /* We increase the RACK ordering window in rounds where we receive
+ * DSACKs that may have been due to reordering causing RACK to trigger
+ * a spurious fast recovery. Thus RACK ignores DSACKs that happen
+ * without having seen reordering, or that match TLP probes (TLP
+ * is timer-driven, not triggered by RACK).
+ */
+ if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
+ tp->rack.dsack_seen = 1;
state->flag |= FLAG_DSACKING_ACK;
/* A spurious retransmission is delivered */
diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
index 6f1b4ac7fe99..fd113f6226ef 100644
--- a/net/ipv4/tcp_recovery.c
+++ b/net/ipv4/tcp_recovery.c
@@ -172,7 +172,8 @@ void tcp_rack_reo_timeout(struct sock *sk)
/* Updates the RACK's reo_wnd based on DSACK and no. of recoveries.
*
- * If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded
+ * If a DSACK is received that seems like it may have been due to reordering
+ * triggering fast recovery, increment reo_wnd by min_rtt/4 (upper bounded
* by srtt), since there is possibility that spurious retransmission was
* due to reordering delay longer than reo_wnd.
*
--
2.32.0.432.gabb21c7263-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP
2021-07-27 14:42 [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 1/2] tcp: more accurately detect spurious TLP probes Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 2/2] tcp: more accurately check DSACKs to grow RACK reordering window Neal Cardwell
@ 2021-07-27 19:20 ` patchwork-bot+netdevbpf
2 siblings, 0 replies; 4+ messages in thread
From: patchwork-bot+netdevbpf @ 2021-07-27 19:20 UTC (permalink / raw)
To: Neal Cardwell; +Cc: davem, netdev, edumazet
Hello:
This series was applied to netdev/net-next.git (refs/heads/master):
On Tue, 27 Jul 2021 10:42:56 -0400 you wrote:
> This patch series includes two minor improvements to tighten up the accuracy of
> the processing of incoming DSACK information, so that RACK-TLP behavior is
> faster and more precise: first, to ensure we detect packet loss in some extra
> corner cases; and second, to avoid growing the RACK reordering window (and
> delaying fast recovery) in cases where it seems clear we don't need to.
>
> Neal Cardwell (1):
> tcp: more accurately check DSACKs to grow RACK reordering window
>
> [...]
Here is the summary with links:
- [net-next,1/2] tcp: more accurately detect spurious TLP probes
https://git.kernel.org/netdev/net-next/c/63f367d9de77
- [net-next,2/2] tcp: more accurately check DSACKs to grow RACK reordering window
https://git.kernel.org/netdev/net-next/c/a657db0350bb
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-07-27 14:42 [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 1/2] tcp: more accurately detect spurious TLP probes Neal Cardwell
2021-07-27 14:42 ` [PATCH net-next 2/2] tcp: more accurately check DSACKs to grow RACK reordering window Neal Cardwell
2021-07-27 19:20 ` [PATCH net-next 0/2] more accurate DSACK processing for RACK-TLP patchwork-bot+netdevbpf
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