netdev - Re: [PATCH v2 2/3] nvme-tcp: support specifying the congestion-control

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20220314093429.00005b95@tom.com>
Date:   Mon, 14 Mar 2022 09:34:29 +0800
From:   Mingbao Sun <sunmingbao@....com>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     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,
        tyler.sun@...l.com, ping.gan@...l.com, yanxiu.cai@...l.com,
        libin.zhang@...l.com, ao.sun@...l.com
Subject: Re: [PATCH v2 2/3] nvme-tcp: support specifying the
 congestion-control

Before answering the questions, I’d like to address the motivation
behind this patchset.

You know, InfiniBand/RoCE provides NVMe-oF a lossless network
environment (that is zero packet loss), which is a great advantage
to performance.

In contrast, 'TCP/IP + ethernet' is often used as a lossy network
environment (packet dropping often occurs). 
And once packet dropping occurs, timeout-retransmission would be
triggered. But once timeout-retransmission was triggered, bandwidth
would drop to 0 all of a sudden. This is great damage to performance.

So although NVMe/TCP may have a bandwidth competitive to that of
NVMe/RDMA, but the packet dropping of the former is a flaw to
its performance.

However, with the combination of the following conditions, NVMe/TCP
can become much more competitive to NVMe/RDMA in the data center.

  - Ethernet NICs supporting QoS configuration (support mapping TOS/DSCP
    in IP header into priority, supporting adjusting buffer size of each
    priority, support PFC)

  - Ethernet Switches supporting ECN marking, supporting adjusting
    buffer size of each priority.

  - NVMe/TCP supports specifying the tos for its TCP traffic
    (already implemented)

  - NVMe/TCP supports specifying dctcp as the congestion-control of its
    TCP sockets (the work of this feature)

So this feature is the last item from the software aspect to form up the
above combination.