netdev - Re: [PATCH net-next v2] tcp: force cwnd at least 2 in tcp_cwnd

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Date:   Wed, 27 Jun 2018 08:06:39 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Lawrence Brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>
Cc:     Kernel Team <kernel-team@...com>, Blake Matheny <bmatheny@...com>,
        Alexei Starovoitov <ast@...com>
Subject: Re: [PATCH net-next v2] tcp: force cwnd at least 2 in
 tcp_cwnd_reduction



On 06/27/2018 08:04 AM, Eric Dumazet wrote:
> 
> 
> On 06/26/2018 07:34 PM, Lawrence Brakmo wrote:
>> When using dctcp and doing RPCs, if the last packet of a request is
>> ECN marked as having seen congestion (CE), the sender can decrease its
>> cwnd to 1. As a result, it will only send one packet when a new request
>> is sent. In some instances this results in high tail latencies.
>>
> 
>>  	}
>>  	/* Force a fast retransmit upon entering fast recovery */
>>  	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
>> -	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
>> +	tp->snd_cwnd = max((int)tcp_packets_in_flight(tp) + sndcnt, 2);
> 
> Canonical way is to use min_t(), please respin (no need to explain this trivia in changelog)


Well, max_t() here, obviously :)