netdev - Re: [PATCH net-next 0/8] improving TCP behavior on host congestion

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Date:   Thu, 17 Jan 2019 15:12:40 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     ycheng@...gle.com
Cc:     edumazet@...gle.com, netdev@...r.kernel.org, ncardwell@...gle.com,
        soheil@...gle.com
Subject: Re: [PATCH net-next 0/8] improving TCP behavior on host congestion

From: Yuchung Cheng <ycheng@...gle.com>
Date: Wed, 16 Jan 2019 15:05:27 -0800

> This patch set aims to improve how TCP handle local qdisc congestion
> by simplifying the previous implementation.  Previously when an
> skb fails to (re)transmit due to local qdisc congestion or other
> resource issue, TCP refrains from setting the skb timestamp or the
> recovery starting time.
> 
> This design makes determining when to abort a stalling socket more
> complicated, as the timestamps of these tranmission attempts were
> missing. The stack needs to sort of infer when the original attempt
> happens. A by-product is a socket may disregard the system timeout
> limit (i.e. sysctl net.ipv4.tcp_retries2 or USER_TIMEOUT option),
> and continue to retry until the transmission is successful.
> 
> In data-center environment when TCP RTO is small, this could cause
> the socket to retry frequently for long during qdisc congestion.
> 
> The solution is to first unconditionally timestamp skb and recovery
> attempt. Then retry more conservatively (twice a second) on local
> qdisc congestion but abort the sockets according to the system limit.

Series applied, thanks.