* [PATCH net-next] tcp: improve PRR loss recovery
@ 2022-05-19 0:34 Yuchung Cheng
2022-05-20 2:10 ` patchwork-bot+netdevbpf
0 siblings, 1 reply; 2+ messages in thread
From: Yuchung Cheng @ 2022-05-19 0:34 UTC (permalink / raw)
To: davem; +Cc: netdev, edumazet, ncardwell, Yuchung Cheng
This patch improves TCP PRR loss recovery behavior for a corner
case. Previously during PRR conservation-bound mode, it strictly
sends the amount equals to the amount newly acked or s/acked.
The patch changes s.t. PRR may send additional amount that was banked
previously (e.g. application-limited) in the conservation-bound
mode, similar to the slow-start mode. This unifies and simplifies the
algorithm further and may improve the recovery latency. This change
still follow the general packet conservation design principle and
always keep inflight/cwnd below the slow start threshold set
by the congestion control module.
PRR is described in RFC 6937. We'll include this change in the
latest revision rfc6937-bis as well.
Reported-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
net/ipv4/tcp_input.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 97cfcd85f84e..3231af73e430 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2620,12 +2620,12 @@ void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost,
u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
tp->prior_cwnd - 1;
sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
- } else if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost) {
- sndcnt = min_t(int, delta,
- max_t(int, tp->prr_delivered - tp->prr_out,
- newly_acked_sacked) + 1);
} else {
- sndcnt = min(delta, newly_acked_sacked);
+ sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
+ newly_acked_sacked);
+ if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
+ sndcnt++;
+ sndcnt = min(delta, sndcnt);
}
/* Force a fast retransmit upon entering fast recovery */
sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
--
2.36.1.124.g0e6072fb45-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net-next] tcp: improve PRR loss recovery
2022-05-19 0:34 [PATCH net-next] tcp: improve PRR loss recovery Yuchung Cheng
@ 2022-05-20 2:10 ` patchwork-bot+netdevbpf
0 siblings, 0 replies; 2+ messages in thread
From: patchwork-bot+netdevbpf @ 2022-05-20 2:10 UTC (permalink / raw)
To: Yuchung Cheng; +Cc: davem, netdev, edumazet, ncardwell
Hello:
This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:
On Wed, 18 May 2022 17:34:10 -0700 you wrote:
> This patch improves TCP PRR loss recovery behavior for a corner
> case. Previously during PRR conservation-bound mode, it strictly
> sends the amount equals to the amount newly acked or s/acked.
>
> The patch changes s.t. PRR may send additional amount that was banked
> previously (e.g. application-limited) in the conservation-bound
> mode, similar to the slow-start mode. This unifies and simplifies the
> algorithm further and may improve the recovery latency. This change
> still follow the general packet conservation design principle and
> always keep inflight/cwnd below the slow start threshold set
> by the congestion control module.
>
> [...]
Here is the summary with links:
- [net-next] tcp: improve PRR loss recovery
https://git.kernel.org/netdev/net-next/c/9ad084d66619
You are awesome, thank you!
--
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