Messages in this thread | | | Date | Tue, 8 Mar 2022 21:03:20 +0800 | From | Mingbao Sun <> | Subject | Re: [PATCH 0/2] NVMe_over_TCP: support specifying the congestion-control |
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I feel that I'd better address this a little bit more to express the meaning behind this feature.
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, it’s a great damage to the 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 almost be as competitive as NVMe/RDMA in the data center.
- Ethernet NICs supporting QoS configuration (support mapping TOS/DSCP in IP header into 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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