netdev - Re: [PATCH v2 3/3] nvmet-tcp: support specifying the congestion-control

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Date:   Sun, 13 Mar 2022 13:44:11 +0200
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Mingbao Sun <sunmingbao@....com>, Keith Busch <kbusch@...nel.org>,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Chaitanya Kulkarni <kch@...dia.com>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     tyler.sun@...l.com, ping.gan@...l.com, yanxiu.cai@...l.com,
        libin.zhang@...l.com, ao.sun@...l.com
Subject: Re: [PATCH v2 3/3] nvmet-tcp: support specifying the
 congestion-control


> From: Mingbao Sun <tyler.sun@...l.com>

Hey Mingbao,

> congestion-control could have a noticeable impaction on the
> performance of TCP-based communications. This is of course true
> to NVMe_over_TCP.
> 
> Different congestion-controls (e.g., cubic, dctcp) are suitable for
> different scenarios. Proper adoption of congestion control would benefit
> the performance. On the contrary, the performance could be destroyed.
> 
> Though we can specify the congestion-control of NVMe_over_TCP via
> writing '/proc/sys/net/ipv4/tcp_congestion_control', but this also
> changes the congestion-control of all the future TCP sockets that
> have not been explicitly assigned the congestion-control, thus bringing
> potential impaction on their performance.
> 
> So it makes sense to make NVMe_over_TCP support specifying the
> congestion-control. And this commit addresses the target side.
> 
> Implementation approach:
> the following new file entry was created for user to specify the
> congestion-control of each nvmet port.
> '/sys/kernel/config/nvmet/ports/X/tcp_congestion'
> Then later in nvmet_tcp_add_port, the specified congestion-control
> would be applied to the listening socket of the nvmet port.

Please see my comments on the host side patch.

In addition, specifically on the chosen interface, why should this
be port specific? What is the use-case to configure this per-port?