netdev - Re: debugging TCP stalls on high-speed wifi

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Message-ID: <9f984cda-2209-fa07-569e-2555ef2aa78d@gmail.com>
Date:   Fri, 24 Jan 2020 15:49:15 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Johannes Berg <johannes@...solutions.net>,
        Krishna Chaitanya <chaitanya.mgit@...il.com>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: debugging TCP stalls on high-speed wifi



On 1/24/20 2:34 AM, Johannes Berg wrote:
> On Fri, 2019-12-13 at 14:40 +0530, Krishna Chaitanya wrote:
>>
>> Maybe try 'reno' instead of 'cubic' to see if congestion control is
>> being too careful?
> 
> I played around with this a bit now, but apart from a few outliers, the
> congestion control algorithm doesn't have much effect. The outliers are
> 
>  * vegas with ~120 Mbps
>  * nv with ~300 Mbps
>  * cdg with ~600 Mbps
> 
> All the others from my list (reno cubic bbr bic cdg dctcp highspeed htcp
> hybla illinois lp nv scalable vegas veno westwood yeah) are within 50
> Mbps or so from each other (around 1.45Gbps).
> 

When the stalls happens, what is causing TCP to resume the xmit ?

Some tcpdump traces could help.

(-s 100 to only capture headers)