netdev - Re: [PATCH net] tcp: allow at most one TLP probe per flight

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Message-Id: <20200723.122416.892926303358645003.davem@davemloft.net>
Date:   Thu, 23 Jul 2020 12:24:16 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ycheng@...gle.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, ncardwell@...gle.com
Subject: Re: [PATCH net] tcp: allow at most one TLP probe per flight

From: Yuchung Cheng <ycheng@...gle.com>
Date: Thu, 23 Jul 2020 12:00:06 -0700

> Previously TLP may send multiple probes of new data in one
> flight. This happens when the sender is cwnd limited. After the
> initial TLP containing new data is sent, the sender receives another
> ACK that acks partial inflight.  It may re-arm another TLP timer
> to send more, if no further ACK returns before the next TLP timeout
> (PTO) expires. The sender may send in theory a large amount of TLP
> until send queue is depleted. This only happens if the sender sees
> such irregular uncommon ACK pattern. But it is generally undesirable
> behavior during congestion especially.
> 
> The original TLP design restrict only one TLP probe per inflight as
> published in "Reducing Web Latency: the Virtue of Gentle Aggression",
> SIGCOMM 2013. This patch changes TLP to send at most one probe
> per inflight.
> 
> Note that if the sender is app-limited, TLP retransmits old data
> and did not have this issue.
> 
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable, thanks!