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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.
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